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- <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
- <html>
- <head>
- <title>Lua 5.2 Reference Manual</title>
- <link rel="stylesheet" type="text/css" href="lua.css">
- <link rel="stylesheet" type="text/css" href="manual.css">
- <META HTTP-EQUIV="content-type" CONTENT="text/html; charset=iso-8859-1">
- </head>
- <body>
- <hr>
- <h1>
- <a href="http://www.lua.org/"><img src="logo.gif" alt="" border="0"></a>
- Lua 5.2 Reference Manual
- </h1>
- by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes
- <p>
- <small>
- Copyright © 2011–2015 Lua.org, PUC-Rio.
- Freely available under the terms of the
- <a href="http://www.lua.org/license.html">Lua license</a>.
- </small>
- <hr>
- <p>
- <a href="contents.html#contents">contents</A>
- ·
- <a href="contents.html#index">index</A>
- <!-- ====================================================================== -->
- <p>
- <!-- $Id: manual.of,v 1.104 2013/06/01 00:13:11 roberto Exp $ -->
- <h1>1 – <a name="1">Introduction</a></h1>
- <p>
- Lua is an extension programming language designed to support
- general procedural programming with data description
- facilities.
- It also offers good support for object-oriented programming,
- functional programming, and data-driven programming.
- Lua is intended to be used as a powerful, lightweight,
- embeddable scripting language for any program that needs one.
- Lua is implemented as a library, written in <em>clean C</em>,
- the common subset of Standard C and C++.
- <p>
- Being an extension language, Lua has no notion of a "main" program:
- it only works <em>embedded</em> in a host client,
- called the <em>embedding program</em> or simply the <em>host</em>.
- The host program can invoke functions to execute a piece of Lua code,
- can write and read Lua variables,
- and can register C functions to be called by Lua code.
- Through the use of C functions, Lua can be augmented to cope with
- a wide range of different domains,
- thus creating customized programming languages sharing a syntactical framework.
- The Lua distribution includes a sample host program called <code>lua</code>,
- which uses the Lua library to offer a complete, standalone Lua interpreter,
- for interactive or batch use.
- <p>
- Lua is free software,
- and is provided as usual with no guarantees,
- as stated in its license.
- The implementation described in this manual is available
- at Lua's official web site, <code>www.lua.org</code>.
- <p>
- Like any other reference manual,
- this document is dry in places.
- For a discussion of the decisions behind the design of Lua,
- see the technical papers available at Lua's web site.
- For a detailed introduction to programming in Lua,
- see Roberto's book, <em>Programming in Lua</em>.
- <h1>2 – <a name="2">Basic Concepts</a></h1>
- <p>
- This section describes the basic concepts of the language.
- <h2>2.1 – <a name="2.1">Values and Types</a></h2>
- <p>
- Lua is a <em>dynamically typed language</em>.
- This means that
- variables do not have types; only values do.
- There are no type definitions in the language.
- All values carry their own type.
- <p>
- All values in Lua are <em>first-class values</em>.
- This means that all values can be stored in variables,
- passed as arguments to other functions, and returned as results.
- <p>
- There are eight basic types in Lua:
- <em>nil</em>, <em>boolean</em>, <em>number</em>,
- <em>string</em>, <em>function</em>, <em>userdata</em>,
- <em>thread</em>, and <em>table</em>.
- <em>Nil</em> is the type of the value <b>nil</b>,
- whose main property is to be different from any other value;
- it usually represents the absence of a useful value.
- <em>Boolean</em> is the type of the values <b>false</b> and <b>true</b>.
- Both <b>nil</b> and <b>false</b> make a condition false;
- any other value makes it true.
- <em>Number</em> represents real (double-precision floating-point) numbers.
- Operations on numbers follow the same rules of
- the underlying C implementation,
- which, in turn, usually follows the IEEE 754 standard.
- (It is easy to build Lua interpreters that use other
- internal representations for numbers,
- such as single-precision floats or long integers;
- see file <code>luaconf.h</code>.)
- <em>String</em> represents immutable sequences of bytes.
- Lua is 8-bit clean:
- strings can contain any 8-bit value,
- including embedded zeros ('<code>\0</code>').
- <p>
- Lua can call (and manipulate) functions written in Lua and
- functions written in C
- (see <a href="#3.4.9">§3.4.9</a>).
- <p>
- The type <em>userdata</em> is provided to allow arbitrary C data to
- be stored in Lua variables.
- A userdata value is a pointer to a block of raw memory.
- There are two kinds of userdata:
- full userdata, where the block of memory is managed by Lua,
- and light userdata, where the block of memory is managed by the host.
- Userdata has no predefined operations in Lua,
- except assignment and identity test.
- By using <em>metatables</em>,
- the programmer can define operations for full userdata values
- (see <a href="#2.4">§2.4</a>).
- Userdata values cannot be created or modified in Lua,
- only through the C API.
- This guarantees the integrity of data owned by the host program.
- <p>
- The type <em>thread</em> represents independent threads of execution
- and it is used to implement coroutines (see <a href="#2.6">§2.6</a>).
- Do not confuse Lua threads with operating-system threads.
- Lua supports coroutines on all systems,
- even those that do not support threads.
- <p>
- The type <em>table</em> implements associative arrays,
- that is, arrays that can be indexed not only with numbers,
- but with any Lua value except <b>nil</b> and NaN
- (<em>Not a Number</em>, a special numeric value used to represent
- undefined or unrepresentable results, such as <code>0/0</code>).
- Tables can be <em>heterogeneous</em>;
- that is, they can contain values of all types (except <b>nil</b>).
- Any key with value <b>nil</b> is not considered part of the table.
- Conversely, any key that is not part of a table has
- an associated value <b>nil</b>.
- <p>
- Tables are the sole data structuring mechanism in Lua;
- they can be used to represent ordinary arrays, sequences,
- symbol tables, sets, records, graphs, trees, etc.
- To represent records, Lua uses the field name as an index.
- The language supports this representation by
- providing <code>a.name</code> as syntactic sugar for <code>a["name"]</code>.
- There are several convenient ways to create tables in Lua
- (see <a href="#3.4.8">§3.4.8</a>).
- <p>
- We use the term <em>sequence</em> to denote a table where
- the set of all positive numeric keys is equal to <em>{1..n}</em>
- for some integer <em>n</em>,
- which is called the length of the sequence (see <a href="#3.4.6">§3.4.6</a>).
- <p>
- Like indices,
- the values of table fields can be of any type.
- In particular,
- because functions are first-class values,
- table fields can contain functions.
- Thus tables can also carry <em>methods</em> (see <a href="#3.4.10">§3.4.10</a>).
- <p>
- The indexing of tables follows
- the definition of raw equality in the language.
- The expressions <code>a[i]</code> and <code>a[j]</code>
- denote the same table element
- if and only if <code>i</code> and <code>j</code> are raw equal
- (that is, equal without metamethods).
- <p>
- Tables, functions, threads, and (full) userdata values are <em>objects</em>:
- variables do not actually <em>contain</em> these values,
- only <em>references</em> to them.
- Assignment, parameter passing, and function returns
- always manipulate references to such values;
- these operations do not imply any kind of copy.
- <p>
- The library function <a href="#pdf-type"><code>type</code></a> returns a string describing the type
- of a given value (see <a href="#6.1">§6.1</a>).
- <h2>2.2 – <a name="2.2">Environments and the Global Environment</a></h2>
- <p>
- As will be discussed in <a href="#3.2">§3.2</a> and <a href="#3.3.3">§3.3.3</a>,
- any reference to a global name <code>var</code> is syntactically translated
- to <code>_ENV.var</code>.
- Moreover, every chunk is compiled in the scope of
- an external local variable called <code>_ENV</code> (see <a href="#3.3.2">§3.3.2</a>),
- so <code>_ENV</code> itself is never a global name in a chunk.
- <p>
- Despite the existence of this external <code>_ENV</code> variable and
- the translation of global names,
- <code>_ENV</code> is a completely regular name.
- In particular,
- you can define new variables and parameters with that name.
- Each reference to a global name uses the <code>_ENV</code> that is
- visible at that point in the program,
- following the usual visibility rules of Lua (see <a href="#3.5">§3.5</a>).
- <p>
- Any table used as the value of <code>_ENV</code> is called an <em>environment</em>.
- <p>
- Lua keeps a distinguished environment called the <em>global environment</em>.
- This value is kept at a special index in the C registry (see <a href="#4.5">§4.5</a>).
- In Lua, the variable <a href="#pdf-_G"><code>_G</code></a> is initialized with this same value.
- <p>
- When Lua compiles a chunk,
- it initializes the value of its <code>_ENV</code> upvalue
- with the global environment (see <a href="#pdf-load"><code>load</code></a>).
- Therefore, by default,
- global variables in Lua code refer to entries in the global environment.
- Moreover, all standard libraries are loaded in the global environment
- and several functions there operate on that environment.
- You can use <a href="#pdf-load"><code>load</code></a> (or <a href="#pdf-loadfile"><code>loadfile</code></a>)
- to load a chunk with a different environment.
- (In C, you have to load the chunk and then change the value
- of its first upvalue.)
- <p>
- If you change the global environment in the registry
- (through C code or the debug library),
- all chunks loaded after the change will get the new environment.
- Previously loaded chunks are not affected, however,
- as each has its own reference to the environment in its <code>_ENV</code> variable.
- Moreover, the variable <a href="#pdf-_G"><code>_G</code></a>
- (which is stored in the original global environment)
- is never updated by Lua.
- <h2>2.3 – <a name="2.3">Error Handling</a></h2>
- <p>
- Because Lua is an embedded extension language,
- all Lua actions start from C code in the host program
- calling a function from the Lua library (see <a href="#lua_pcall"><code>lua_pcall</code></a>).
- Whenever an error occurs during
- the compilation or execution of a Lua chunk,
- control returns to the host,
- which can take appropriate measures
- (such as printing an error message).
- <p>
- Lua code can explicitly generate an error by calling the
- <a href="#pdf-error"><code>error</code></a> function.
- If you need to catch errors in Lua,
- you can use <a href="#pdf-pcall"><code>pcall</code></a> or <a href="#pdf-xpcall"><code>xpcall</code></a>
- to call a given function in <em>protected mode</em>.
- <p>
- Whenever there is an error,
- an <em>error object</em> (also called an <em>error message</em>)
- is propagated with information about the error.
- Lua itself only generates errors where the error object is a string,
- but programs may generate errors with
- any value for the error object.
- <p>
- When you use <a href="#pdf-xpcall"><code>xpcall</code></a> or <a href="#lua_pcall"><code>lua_pcall</code></a>,
- you may give a <em>message handler</em>
- to be called in case of errors.
- This function is called with the original error message
- and returns a new error message.
- It is called before the error unwinds the stack,
- so that it can gather more information about the error,
- for instance by inspecting the stack and creating a stack traceback.
- This message handler is still protected by the protected call;
- so, an error inside the message handler
- will call the message handler again.
- If this loop goes on, Lua breaks it and returns an appropriate message.
- <h2>2.4 – <a name="2.4">Metatables and Metamethods</a></h2>
- <p>
- Every value in Lua can have a <em>metatable</em>.
- This <em>metatable</em> is an ordinary Lua table
- that defines the behavior of the original value
- under certain special operations.
- You can change several aspects of the behavior
- of operations over a value by setting specific fields in its metatable.
- For instance, when a non-numeric value is the operand of an addition,
- Lua checks for a function in the field "<code>__add</code>" of the value's metatable.
- If it finds one,
- Lua calls this function to perform the addition.
- <p>
- The keys in a metatable are derived from the <em>event</em> names;
- the corresponding values are called <em>metamethods</em>.
- In the previous example, the event is <code>"add"</code>
- and the metamethod is the function that performs the addition.
- <p>
- You can query the metatable of any value
- using the <a href="#pdf-getmetatable"><code>getmetatable</code></a> function.
- <p>
- You can replace the metatable of tables
- using the <a href="#pdf-setmetatable"><code>setmetatable</code></a> function.
- You cannot change the metatable of other types from Lua
- (except by using the debug library);
- you must use the C API for that.
- <p>
- Tables and full userdata have individual metatables
- (although multiple tables and userdata can share their metatables).
- Values of all other types share one single metatable per type;
- that is, there is one single metatable for all numbers,
- one for all strings, etc.
- By default, a value has no metatable,
- but the string library sets a metatable for the string type (see <a href="#6.4">§6.4</a>).
- <p>
- A metatable controls how an object behaves in arithmetic operations,
- order comparisons, concatenation, length operation, and indexing.
- A metatable also can define a function to be called
- when a userdata or a table is garbage collected.
- When Lua performs one of these operations over a value,
- it checks whether this value has a metatable with the corresponding event.
- If so, the value associated with that key (the metamethod)
- controls how Lua will perform the operation.
- <p>
- Metatables control the operations listed next.
- Each operation is identified by its corresponding name.
- The key for each operation is a string with its name prefixed by
- two underscores, '<code>__</code>';
- for instance, the key for operation "add" is the
- string "<code>__add</code>".
- <p>
- The semantics of these operations is better explained by a Lua function
- describing how the interpreter executes the operation.
- The code shown here in Lua is only illustrative;
- the real behavior is hard coded in the interpreter
- and it is much more efficient than this simulation.
- All functions used in these descriptions
- (<a href="#pdf-rawget"><code>rawget</code></a>, <a href="#pdf-tonumber"><code>tonumber</code></a>, etc.)
- are described in <a href="#6.1">§6.1</a>.
- In particular, to retrieve the metamethod of a given object,
- we use the expression
- <pre>
- metatable(obj)[event]
- </pre><p>
- This should be read as
- <pre>
- rawget(getmetatable(obj) or {}, event)
- </pre><p>
- This means that the access to a metamethod does not invoke other metamethods,
- and access to objects with no metatables does not fail
- (it simply results in <b>nil</b>).
- <p>
- For the unary <code>-</code> and <code>#</code> operators,
- the metamethod is called with a dummy second argument.
- This extra argument is only to simplify Lua's internals;
- it may be removed in future versions and therefore it is not present
- in the following code.
- (For most uses this extra argument is irrelevant.)
- <ul>
- <li><b>"add": </b>
- the <code>+</code> operation.
- <p>
- The function <code>getbinhandler</code> below defines how Lua chooses a handler
- for a binary operation.
- First, Lua tries the first operand.
- If its type does not define a handler for the operation,
- then Lua tries the second operand.
- <pre>
- function getbinhandler (op1, op2, event)
- return metatable(op1)[event] or metatable(op2)[event]
- end
- </pre><p>
- By using this function,
- the behavior of the <code>op1 + op2</code> is
- <pre>
- function add_event (op1, op2)
- local o1, o2 = tonumber(op1), tonumber(op2)
- if o1 and o2 then -- both operands are numeric?
- return o1 + o2 -- '+' here is the primitive 'add'
- else -- at least one of the operands is not numeric
- local h = getbinhandler(op1, op2, "__add")
- if h then
- -- call the handler with both operands
- return (h(op1, op2))
- else -- no handler available: default behavior
- error(···)
- end
- end
- end
- </pre><p>
- </li>
- <li><b>"sub": </b>
- the <code>-</code> operation.
- Behavior similar to the "add" operation.
- </li>
- <li><b>"mul": </b>
- the <code>*</code> operation.
- Behavior similar to the "add" operation.
- </li>
- <li><b>"div": </b>
- the <code>/</code> operation.
- Behavior similar to the "add" operation.
- </li>
- <li><b>"mod": </b>
- the <code>%</code> operation.
- Behavior similar to the "add" operation,
- with the operation
- <code>o1 - floor(o1/o2)*o2</code> as the primitive operation.
- </li>
- <li><b>"pow": </b>
- the <code>^</code> (exponentiation) operation.
- Behavior similar to the "add" operation,
- with the function <code>pow</code> (from the C math library)
- as the primitive operation.
- </li>
- <li><b>"unm": </b>
- the unary <code>-</code> operation.
- <pre>
- function unm_event (op)
- local o = tonumber(op)
- if o then -- operand is numeric?
- return -o -- '-' here is the primitive 'unm'
- else -- the operand is not numeric.
- -- Try to get a handler from the operand
- local h = metatable(op).__unm
- if h then
- -- call the handler with the operand
- return (h(op))
- else -- no handler available: default behavior
- error(···)
- end
- end
- end
- </pre><p>
- </li>
- <li><b>"concat": </b>
- the <code>..</code> (concatenation) operation.
- <pre>
- function concat_event (op1, op2)
- if (type(op1) == "string" or type(op1) == "number") and
- (type(op2) == "string" or type(op2) == "number") then
- return op1 .. op2 -- primitive string concatenation
- else
- local h = getbinhandler(op1, op2, "__concat")
- if h then
- return (h(op1, op2))
- else
- error(···)
- end
- end
- end
- </pre><p>
- </li>
- <li><b>"len": </b>
- the <code>#</code> operation.
- <pre>
- function len_event (op)
- if type(op) == "string" then
- return strlen(op) -- primitive string length
- else
- local h = metatable(op).__len
- if h then
- return (h(op)) -- call handler with the operand
- elseif type(op) == "table" then
- return #op -- primitive table length
- else -- no handler available: error
- error(···)
- end
- end
- end
- </pre><p>
- See <a href="#3.4.6">§3.4.6</a> for a description of the length of a table.
- </li>
- <li><b>"eq": </b>
- the <code>==</code> operation.
- The function <code>getequalhandler</code> defines how Lua chooses a metamethod
- for equality.
- A metamethod is selected only when both values
- being compared have the same type
- and the same metamethod for the selected operation,
- and the values are either tables or full userdata.
- <pre>
- function getequalhandler (op1, op2)
- if type(op1) ~= type(op2) or
- (type(op1) ~= "table" and type(op1) ~= "userdata") then
- return nil -- different values
- end
- local mm1 = metatable(op1).__eq
- local mm2 = metatable(op2).__eq
- if mm1 == mm2 then return mm1 else return nil end
- end
- </pre><p>
- The "eq" event is defined as follows:
- <pre>
- function eq_event (op1, op2)
- if op1 == op2 then -- primitive equal?
- return true -- values are equal
- end
- -- try metamethod
- local h = getequalhandler(op1, op2)
- if h then
- return not not h(op1, op2)
- else
- return false
- end
- end
- </pre><p>
- Note that the result is always a boolean.
- </li>
- <li><b>"lt": </b>
- the <code><</code> operation.
- <pre>
- function lt_event (op1, op2)
- if type(op1) == "number" and type(op2) == "number" then
- return op1 < op2 -- numeric comparison
- elseif type(op1) == "string" and type(op2) == "string" then
- return op1 < op2 -- lexicographic comparison
- else
- local h = getbinhandler(op1, op2, "__lt")
- if h then
- return not not h(op1, op2)
- else
- error(···)
- end
- end
- end
- </pre><p>
- Note that the result is always a boolean.
- </li>
- <li><b>"le": </b>
- the <code><=</code> operation.
- <pre>
- function le_event (op1, op2)
- if type(op1) == "number" and type(op2) == "number" then
- return op1 <= op2 -- numeric comparison
- elseif type(op1) == "string" and type(op2) == "string" then
- return op1 <= op2 -- lexicographic comparison
- else
- local h = getbinhandler(op1, op2, "__le")
- if h then
- return not not h(op1, op2)
- else
- h = getbinhandler(op1, op2, "__lt")
- if h then
- return not h(op2, op1)
- else
- error(···)
- end
- end
- end
- end
- </pre><p>
- Note that, in the absence of a "le" metamethod,
- Lua tries the "lt", assuming that <code>a <= b</code> is
- equivalent to <code>not (b < a)</code>.
- <p>
- As with the other comparison operators,
- the result is always a boolean.
- </li>
- <li><b>"index": </b>
- The indexing access <code>table[key]</code>.
- Note that the metamethod is tried only
- when <code>key</code> is not present in <code>table</code>.
- (When <code>table</code> is not a table,
- no key is ever present,
- so the metamethod is always tried.)
- <pre>
- function gettable_event (table, key)
- local h
- if type(table) == "table" then
- local v = rawget(table, key)
- -- if key is present, return raw value
- if v ~= nil then return v end
- h = metatable(table).__index
- if h == nil then return nil end
- else
- h = metatable(table).__index
- if h == nil then
- error(···)
- end
- end
- if type(h) == "function" then
- return (h(table, key)) -- call the handler
- else return h[key] -- or repeat operation on it
- end
- end
- </pre><p>
- </li>
- <li><b>"newindex": </b>
- The indexing assignment <code>table[key] = value</code>.
- Note that the metamethod is tried only
- when <code>key</code> is not present in <code>table</code>.
- <pre>
- function settable_event (table, key, value)
- local h
- if type(table) == "table" then
- local v = rawget(table, key)
- -- if key is present, do raw assignment
- if v ~= nil then rawset(table, key, value); return end
- h = metatable(table).__newindex
- if h == nil then rawset(table, key, value); return end
- else
- h = metatable(table).__newindex
- if h == nil then
- error(···)
- end
- end
- if type(h) == "function" then
- h(table, key,value) -- call the handler
- else h[key] = value -- or repeat operation on it
- end
- end
- </pre><p>
- </li>
- <li><b>"call": </b>
- called when Lua calls a value.
- <pre>
- function function_event (func, ...)
- if type(func) == "function" then
- return func(...) -- primitive call
- else
- local h = metatable(func).__call
- if h then
- return h(func, ...)
- else
- error(···)
- end
- end
- end
- </pre><p>
- </li>
- </ul>
- <h2>2.5 – <a name="2.5">Garbage Collection</a></h2>
- <p>
- Lua performs automatic memory management.
- This means that
- you have to worry neither about allocating memory for new objects
- nor about freeing it when the objects are no longer needed.
- Lua manages memory automatically by running
- a <em>garbage collector</em> to collect all <em>dead objects</em>
- (that is, objects that are no longer accessible from Lua).
- All memory used by Lua is subject to automatic management:
- strings, tables, userdata, functions, threads, internal structures, etc.
- <p>
- Lua implements an incremental mark-and-sweep collector.
- It uses two numbers to control its garbage-collection cycles:
- the <em>garbage-collector pause</em> and
- the <em>garbage-collector step multiplier</em>.
- Both use percentage points as units
- (e.g., a value of 100 means an internal value of 1).
- <p>
- The garbage-collector pause
- controls how long the collector waits before starting a new cycle.
- Larger values make the collector less aggressive.
- Values smaller than 100 mean the collector will not wait to
- start a new cycle.
- A value of 200 means that the collector waits for the total memory in use
- to double before starting a new cycle.
- <p>
- The garbage-collector step multiplier
- controls the relative speed of the collector relative to
- memory allocation.
- Larger values make the collector more aggressive but also increase
- the size of each incremental step.
- Values smaller than 100 make the collector too slow and
- can result in the collector never finishing a cycle.
- The default is 200,
- which means that the collector runs at "twice"
- the speed of memory allocation.
- <p>
- If you set the step multiplier to a very large number
- (larger than 10% of the maximum number of
- bytes that the program may use),
- the collector behaves like a stop-the-world collector.
- If you then set the pause to 200,
- the collector behaves as in old Lua versions,
- doing a complete collection every time Lua doubles its
- memory usage.
- <p>
- You can change these numbers by calling <a href="#lua_gc"><code>lua_gc</code></a> in C
- or <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> in Lua.
- You can also use these functions to control
- the collector directly (e.g., stop and restart it).
- <p>
- As an experimental feature in Lua 5.2,
- you can change the collector's operation mode
- from incremental to <em>generational</em>.
- A <em>generational collector</em> assumes that most objects die young,
- and therefore it traverses only young (recently created) objects.
- This behavior can reduce the time used by the collector,
- but also increases memory usage (as old dead objects may accumulate).
- To mitigate this second problem,
- from time to time the generational collector performs a full collection.
- Remember that this is an experimental feature;
- you are welcome to try it,
- but check your gains.
- <h3>2.5.1 – <a name="2.5.1">Garbage-Collection Metamethods</a></h3>
- <p>
- You can set garbage-collector metamethods for tables
- and, using the C API,
- for full userdata (see <a href="#2.4">§2.4</a>).
- These metamethods are also called <em>finalizers</em>.
- Finalizers allow you to coordinate Lua's garbage collection
- with external resource management
- (such as closing files, network or database connections,
- or freeing your own memory).
- <p>
- For an object (table or userdata) to be finalized when collected,
- you must <em>mark</em> it for finalization.
- You mark an object for finalization when you set its metatable
- and the metatable has a field indexed by the string "<code>__gc</code>".
- Note that if you set a metatable without a <code>__gc</code> field
- and later create that field in the metatable,
- the object will not be marked for finalization.
- However, after an object is marked,
- you can freely change the <code>__gc</code> field of its metatable.
- <p>
- When a marked object becomes garbage,
- it is not collected immediately by the garbage collector.
- Instead, Lua puts it in a list.
- After the collection,
- Lua does the equivalent of the following function
- for each object in that list:
- <pre>
- function gc_event (obj)
- local h = metatable(obj).__gc
- if type(h) == "function" then
- h(obj)
- end
- end
- </pre>
- <p>
- At the end of each garbage-collection cycle,
- the finalizers for objects are called in
- the reverse order that they were marked for collection,
- among those collected in that cycle;
- that is, the first finalizer to be called is the one associated
- with the object marked last in the program.
- The execution of each finalizer may occur at any point during
- the execution of the regular code.
- <p>
- Because the object being collected must still be used by the finalizer,
- it (and other objects accessible only through it)
- must be <em>resurrected</em> by Lua.
- Usually, this resurrection is transient,
- and the object memory is freed in the next garbage-collection cycle.
- However, if the finalizer stores the object in some global place
- (e.g., a global variable),
- then there is a permanent resurrection.
- In any case,
- the object memory is freed only when it becomes completely inaccessible;
- its finalizer will never be called twice.
- <p>
- When you close a state (see <a href="#lua_close"><code>lua_close</code></a>),
- Lua calls the finalizers of all objects marked for finalization,
- following the reverse order that they were marked.
- If any finalizer marks new objects for collection during that phase,
- these new objects will not be finalized.
- <h3>2.5.2 – <a name="2.5.2">Weak Tables</a></h3>
- <p>
- A <em>weak table</em> is a table whose elements are
- <em>weak references</em>.
- A weak reference is ignored by the garbage collector.
- In other words,
- if the only references to an object are weak references,
- then the garbage collector will collect that object.
- <p>
- A weak table can have weak keys, weak values, or both.
- A table with weak keys allows the collection of its keys,
- but prevents the collection of its values.
- A table with both weak keys and weak values allows the collection of
- both keys and values.
- In any case, if either the key or the value is collected,
- the whole pair is removed from the table.
- The weakness of a table is controlled by the
- <code>__mode</code> field of its metatable.
- If the <code>__mode</code> field is a string containing the character '<code>k</code>',
- the keys in the table are weak.
- If <code>__mode</code> contains '<code>v</code>',
- the values in the table are weak.
- <p>
- A table with weak keys and strong values
- is also called an <em>ephemeron table</em>.
- In an ephemeron table,
- a value is considered reachable only if its key is reachable.
- In particular,
- if the only reference to a key comes through its value,
- the pair is removed.
- <p>
- Any change in the weakness of a table may take effect only
- at the next collect cycle.
- In particular, if you change the weakness to a stronger mode,
- Lua may still collect some items from that table
- before the change takes effect.
- <p>
- Only objects that have an explicit construction
- are removed from weak tables.
- Values, such as numbers and light C functions,
- are not subject to garbage collection,
- and therefore are not removed from weak tables
- (unless its associated value is collected).
- Although strings are subject to garbage collection,
- they do not have an explicit construction,
- and therefore are not removed from weak tables.
- <p>
- Resurrected objects
- (that is, objects being finalized
- and objects accessible only through objects being finalized)
- have a special behavior in weak tables.
- They are removed from weak values before running their finalizers,
- but are removed from weak keys only in the next collection
- after running their finalizers, when such objects are actually freed.
- This behavior allows the finalizer to access properties
- associated with the object through weak tables.
- <p>
- If a weak table is among the resurrected objects in a collection cycle,
- it may not be properly cleared until the next cycle.
- <h2>2.6 – <a name="2.6">Coroutines</a></h2>
- <p>
- Lua supports coroutines,
- also called <em>collaborative multithreading</em>.
- A coroutine in Lua represents an independent thread of execution.
- Unlike threads in multithread systems, however,
- a coroutine only suspends its execution by explicitly calling
- a yield function.
- <p>
- You create a coroutine by calling <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>.
- Its sole argument is a function
- that is the main function of the coroutine.
- The <code>create</code> function only creates a new coroutine and
- returns a handle to it (an object of type <em>thread</em>);
- it does not start the coroutine.
- <p>
- You execute a coroutine by calling <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
- When you first call <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
- passing as its first argument
- a thread returned by <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
- the coroutine starts its execution,
- at the first line of its main function.
- Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are passed on
- to the coroutine main function.
- After the coroutine starts running,
- it runs until it terminates or <em>yields</em>.
- <p>
- A coroutine can terminate its execution in two ways:
- normally, when its main function returns
- (explicitly or implicitly, after the last instruction);
- and abnormally, if there is an unprotected error.
- In the first case, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>true</b>,
- plus any values returned by the coroutine main function.
- In case of errors, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>false</b>
- plus an error message.
- <p>
- A coroutine yields by calling <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
- When a coroutine yields,
- the corresponding <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns immediately,
- even if the yield happens inside nested function calls
- (that is, not in the main function,
- but in a function directly or indirectly called by the main function).
- In the case of a yield, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> also returns <b>true</b>,
- plus any values passed to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
- The next time you resume the same coroutine,
- it continues its execution from the point where it yielded,
- with the call to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a> returning any extra
- arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
- <p>
- Like <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
- the <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> function also creates a coroutine,
- but instead of returning the coroutine itself,
- it returns a function that, when called, resumes the coroutine.
- Any arguments passed to this function
- go as extra arguments to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
- <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> returns all the values returned by <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
- except the first one (the boolean error code).
- Unlike <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
- <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> does not catch errors;
- any error is propagated to the caller.
- <p>
- As an example of how coroutines work,
- consider the following code:
- <pre>
- function foo (a)
- print("foo", a)
- return coroutine.yield(2*a)
- end
-
- co = coroutine.create(function (a,b)
- print("co-body", a, b)
- local r = foo(a+1)
- print("co-body", r)
- local r, s = coroutine.yield(a+b, a-b)
- print("co-body", r, s)
- return b, "end"
- end)
-
- print("main", coroutine.resume(co, 1, 10))
- print("main", coroutine.resume(co, "r"))
- print("main", coroutine.resume(co, "x", "y"))
- print("main", coroutine.resume(co, "x", "y"))
- </pre><p>
- When you run it, it produces the following output:
- <pre>
- co-body 1 10
- foo 2
- main true 4
- co-body r
- main true 11 -9
- co-body x y
- main true 10 end
- main false cannot resume dead coroutine
- </pre>
- <p>
- You can also create and manipulate coroutines through the C API:
- see functions <a href="#lua_newthread"><code>lua_newthread</code></a>, <a href="#lua_resume"><code>lua_resume</code></a>,
- and <a href="#lua_yield"><code>lua_yield</code></a>.
- <h1>3 – <a name="3">The Language</a></h1>
- <p>
- This section describes the lexis, the syntax, and the semantics of Lua.
- In other words,
- this section describes
- which tokens are valid,
- how they can be combined,
- and what their combinations mean.
- <p>
- Language constructs will be explained using the usual extended BNF notation,
- in which
- {<em>a</em>} means 0 or more <em>a</em>'s, and
- [<em>a</em>] means an optional <em>a</em>.
- Non-terminals are shown like non-terminal,
- keywords are shown like <b>kword</b>,
- and other terminal symbols are shown like ‘<b>=</b>’.
- The complete syntax of Lua can be found in <a href="#9">§9</a>
- at the end of this manual.
- <h2>3.1 – <a name="3.1">Lexical Conventions</a></h2>
- <p>
- Lua is a free-form language.
- It ignores spaces (including new lines) and comments
- between lexical elements (tokens),
- except as delimiters between names and keywords.
- <p>
- <em>Names</em>
- (also called <em>identifiers</em>)
- in Lua can be any string of letters,
- digits, and underscores,
- not beginning with a digit.
- Identifiers are used to name variables, table fields, and labels.
- <p>
- The following <em>keywords</em> are reserved
- and cannot be used as names:
- <pre>
- and break do else elseif end
- false for function goto if in
- local nil not or repeat return
- then true until while
- </pre>
- <p>
- Lua is a case-sensitive language:
- <code>and</code> is a reserved word, but <code>And</code> and <code>AND</code>
- are two different, valid names.
- As a convention, names starting with an underscore followed by
- uppercase letters (such as <a href="#pdf-_VERSION"><code>_VERSION</code></a>)
- are reserved for variables used by Lua.
- <p>
- The following strings denote other tokens:
- <pre>
- + - * / % ^ #
- == ~= <= >= < > =
- ( ) { } [ ] ::
- ; : , . .. ...
- </pre>
- <p>
- <em>Literal strings</em>
- can be delimited by matching single or double quotes,
- and can contain the following C-like escape sequences:
- '<code>\a</code>' (bell),
- '<code>\b</code>' (backspace),
- '<code>\f</code>' (form feed),
- '<code>\n</code>' (newline),
- '<code>\r</code>' (carriage return),
- '<code>\t</code>' (horizontal tab),
- '<code>\v</code>' (vertical tab),
- '<code>\\</code>' (backslash),
- '<code>\"</code>' (quotation mark [double quote]),
- and '<code>\'</code>' (apostrophe [single quote]).
- A backslash followed by a real newline
- results in a newline in the string.
- The escape sequence '<code>\z</code>' skips the following span
- of white-space characters,
- including line breaks;
- it is particularly useful to break and indent a long literal string
- into multiple lines without adding the newlines and spaces
- into the string contents.
- <p>
- A byte in a literal string can also be specified by its numerical value.
- This can be done with the escape sequence <code>\x<em>XX</em></code>,
- where <em>XX</em> is a sequence of exactly two hexadecimal digits,
- or with the escape sequence <code>\<em>ddd</em></code>,
- where <em>ddd</em> is a sequence of up to three decimal digits.
- (Note that if a decimal escape is to be followed by a digit,
- it must be expressed using exactly three digits.)
- Strings in Lua can contain any 8-bit value, including embedded zeros,
- which can be specified as '<code>\0</code>'.
- <p>
- Literal strings can also be defined using a long format
- enclosed by <em>long brackets</em>.
- We define an <em>opening long bracket of level <em>n</em></em> as an opening
- square bracket followed by <em>n</em> equal signs followed by another
- opening square bracket.
- So, an opening long bracket of level 0 is written as <code>[[</code>,
- an opening long bracket of level 1 is written as <code>[=[</code>,
- and so on.
- A <em>closing long bracket</em> is defined similarly;
- for instance, a closing long bracket of level 4 is written as <code>]====]</code>.
- A <em>long literal</em> starts with an opening long bracket of any level and
- ends at the first closing long bracket of the same level.
- It can contain any text except a closing bracket of the proper level.
- Literals in this bracketed form can run for several lines,
- do not interpret any escape sequences,
- and ignore long brackets of any other level.
- Any kind of end-of-line sequence
- (carriage return, newline, carriage return followed by newline,
- or newline followed by carriage return)
- is converted to a simple newline.
- <p>
- Any byte in a literal string not
- explicitly affected by the previous rules represents itself.
- However, Lua opens files for parsing in text mode,
- and the system file functions may have problems with
- some control characters.
- So, it is safer to represent
- non-text data as a quoted literal with
- explicit escape sequences for non-text characters.
- <p>
- For convenience,
- when the opening long bracket is immediately followed by a newline,
- the newline is not included in the string.
- As an example, in a system using ASCII
- (in which '<code>a</code>' is coded as 97,
- newline is coded as 10, and '<code>1</code>' is coded as 49),
- the five literal strings below denote the same string:
- <pre>
- a = 'alo\n123"'
- a = "alo\n123\""
- a = '\97lo\10\04923"'
- a = [[alo
- 123"]]
- a = [==[
- alo
- 123"]==]
- </pre>
- <p>
- A <em>numerical constant</em> can be written with an optional fractional part
- and an optional decimal exponent,
- marked by a letter '<code>e</code>' or '<code>E</code>'.
- Lua also accepts hexadecimal constants,
- which start with <code>0x</code> or <code>0X</code>.
- Hexadecimal constants also accept an optional fractional part
- plus an optional binary exponent,
- marked by a letter '<code>p</code>' or '<code>P</code>'.
- Examples of valid numerical constants are
- <pre>
- 3 3.0 3.1416 314.16e-2 0.31416E1
- 0xff 0x0.1E 0xA23p-4 0X1.921FB54442D18P+1
- </pre>
- <p>
- A <em>comment</em> starts with a double hyphen (<code>--</code>)
- anywhere outside a string.
- If the text immediately after <code>--</code> is not an opening long bracket,
- the comment is a <em>short comment</em>,
- which runs until the end of the line.
- Otherwise, it is a <em>long comment</em>,
- which runs until the corresponding closing long bracket.
- Long comments are frequently used to disable code temporarily.
- <h2>3.2 – <a name="3.2">Variables</a></h2>
- <p>
- Variables are places that store values.
- There are three kinds of variables in Lua:
- global variables, local variables, and table fields.
- <p>
- A single name can denote a global variable or a local variable
- (or a function's formal parameter,
- which is a particular kind of local variable):
- <pre>
- var ::= Name
- </pre><p>
- Name denotes identifiers, as defined in <a href="#3.1">§3.1</a>.
- <p>
- Any variable name is assumed to be global unless explicitly declared
- as a local (see <a href="#3.3.7">§3.3.7</a>).
- Local variables are <em>lexically scoped</em>:
- local variables can be freely accessed by functions
- defined inside their scope (see <a href="#3.5">§3.5</a>).
- <p>
- Before the first assignment to a variable, its value is <b>nil</b>.
- <p>
- Square brackets are used to index a table:
- <pre>
- var ::= prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’
- </pre><p>
- The meaning of accesses to table fields can be changed via metatables.
- An access to an indexed variable <code>t[i]</code> is equivalent to
- a call <code>gettable_event(t,i)</code>.
- (See <a href="#2.4">§2.4</a> for a complete description of the
- <code>gettable_event</code> function.
- This function is not defined or callable in Lua.
- We use it here only for explanatory purposes.)
- <p>
- The syntax <code>var.Name</code> is just syntactic sugar for
- <code>var["Name"]</code>:
- <pre>
- var ::= prefixexp ‘<b>.</b>’ Name
- </pre>
- <p>
- An access to a global variable <code>x</code>
- is equivalent to <code>_ENV.x</code>.
- Due to the way that chunks are compiled,
- <code>_ENV</code> is never a global name (see <a href="#2.2">§2.2</a>).
- <h2>3.3 – <a name="3.3">Statements</a></h2>
- <p>
- Lua supports an almost conventional set of statements,
- similar to those in Pascal or C.
- This set includes
- assignments, control structures, function calls,
- and variable declarations.
- <h3>3.3.1 – <a name="3.3.1">Blocks</a></h3>
- <p>
- A block is a list of statements,
- which are executed sequentially:
- <pre>
- block ::= {stat}
- </pre><p>
- Lua has <em>empty statements</em>
- that allow you to separate statements with semicolons,
- start a block with a semicolon
- or write two semicolons in sequence:
- <pre>
- stat ::= ‘<b>;</b>’
- </pre>
- <p>
- Function calls and assignments
- can start with an open parenthesis.
- This possibility leads to an ambiguity in Lua's grammar.
- Consider the following fragment:
- <pre>
- a = b + c
- (print or io.write)('done')
- </pre><p>
- The grammar could see it in two ways:
- <pre>
- a = b + c(print or io.write)('done')
-
- a = b + c; (print or io.write)('done')
- </pre><p>
- The current parser always sees such constructions
- in the first way,
- interpreting the open parenthesis
- as the start of the arguments to a call.
- To avoid this ambiguity,
- it is a good practice to always precede with a semicolon
- statements that start with a parenthesis:
- <pre>
- ;(print or io.write)('done')
- </pre>
- <p>
- A block can be explicitly delimited to produce a single statement:
- <pre>
- stat ::= <b>do</b> block <b>end</b>
- </pre><p>
- Explicit blocks are useful
- to control the scope of variable declarations.
- Explicit blocks are also sometimes used to
- add a <b>return</b> statement in the middle
- of another block (see <a href="#3.3.4">§3.3.4</a>).
- <h3>3.3.2 – <a name="3.3.2">Chunks</a></h3>
- <p>
- The unit of compilation of Lua is called a <em>chunk</em>.
- Syntactically,
- a chunk is simply a block:
- <pre>
- chunk ::= block
- </pre>
- <p>
- Lua handles a chunk as the body of an anonymous function
- with a variable number of arguments
- (see <a href="#3.4.10">§3.4.10</a>).
- As such, chunks can define local variables,
- receive arguments, and return values.
- Moreover, such anonymous function is compiled as in the
- scope of an external local variable called <code>_ENV</code> (see <a href="#2.2">§2.2</a>).
- The resulting function always has <code>_ENV</code> as its only upvalue,
- even if it does not use that variable.
- <p>
- A chunk can be stored in a file or in a string inside the host program.
- To execute a chunk,
- Lua first precompiles the chunk into instructions for a virtual machine,
- and then it executes the compiled code
- with an interpreter for the virtual machine.
- <p>
- Chunks can also be precompiled into binary form;
- see program <code>luac</code> for details.
- Programs in source and compiled forms are interchangeable;
- Lua automatically detects the file type and acts accordingly.
- <h3>3.3.3 – <a name="3.3.3">Assignment</a></h3>
- <p>
- Lua allows multiple assignments.
- Therefore, the syntax for assignment
- defines a list of variables on the left side
- and a list of expressions on the right side.
- The elements in both lists are separated by commas:
- <pre>
- stat ::= varlist ‘<b>=</b>’ explist
- varlist ::= var {‘<b>,</b>’ var}
- explist ::= exp {‘<b>,</b>’ exp}
- </pre><p>
- Expressions are discussed in <a href="#3.4">§3.4</a>.
- <p>
- Before the assignment,
- the list of values is <em>adjusted</em> to the length of
- the list of variables.
- If there are more values than needed,
- the excess values are thrown away.
- If there are fewer values than needed,
- the list is extended with as many <b>nil</b>'s as needed.
- If the list of expressions ends with a function call,
- then all values returned by that call enter the list of values,
- before the adjustment
- (except when the call is enclosed in parentheses; see <a href="#3.4">§3.4</a>).
- <p>
- The assignment statement first evaluates all its expressions
- and only then are the assignments performed.
- Thus the code
- <pre>
- i = 3
- i, a[i] = i+1, 20
- </pre><p>
- sets <code>a[3]</code> to 20, without affecting <code>a[4]</code>
- because the <code>i</code> in <code>a[i]</code> is evaluated (to 3)
- before it is assigned 4.
- Similarly, the line
- <pre>
- x, y = y, x
- </pre><p>
- exchanges the values of <code>x</code> and <code>y</code>,
- and
- <pre>
- x, y, z = y, z, x
- </pre><p>
- cyclically permutes the values of <code>x</code>, <code>y</code>, and <code>z</code>.
- <p>
- The meaning of assignments to global variables
- and table fields can be changed via metatables.
- An assignment to an indexed variable <code>t[i] = val</code> is equivalent to
- <code>settable_event(t,i,val)</code>.
- (See <a href="#2.4">§2.4</a> for a complete description of the
- <code>settable_event</code> function.
- This function is not defined or callable in Lua.
- We use it here only for explanatory purposes.)
- <p>
- An assignment to a global variable <code>x = val</code>
- is equivalent to the assignment
- <code>_ENV.x = val</code> (see <a href="#2.2">§2.2</a>).
- <h3>3.3.4 – <a name="3.3.4">Control Structures</a></h3><p>
- The control structures
- <b>if</b>, <b>while</b>, and <b>repeat</b> have the usual meaning and
- familiar syntax:
- <pre>
- stat ::= <b>while</b> exp <b>do</b> block <b>end</b>
- stat ::= <b>repeat</b> block <b>until</b> exp
- stat ::= <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b>
- </pre><p>
- Lua also has a <b>for</b> statement, in two flavors (see <a href="#3.3.5">§3.3.5</a>).
- <p>
- The condition expression of a
- control structure can return any value.
- Both <b>false</b> and <b>nil</b> are considered false.
- All values different from <b>nil</b> and <b>false</b> are considered true
- (in particular, the number 0 and the empty string are also true).
- <p>
- In the <b>repeat</b>–<b>until</b> loop,
- the inner block does not end at the <b>until</b> keyword,
- but only after the condition.
- So, the condition can refer to local variables
- declared inside the loop block.
- <p>
- The <b>goto</b> statement transfers the program control to a label.
- For syntactical reasons,
- labels in Lua are considered statements too:
- <pre>
- stat ::= <b>goto</b> Name
- stat ::= label
- label ::= ‘<b>::</b>’ Name ‘<b>::</b>’
- </pre>
- <p>
- A label is visible in the entire block where it is defined,
- except
- inside nested blocks where a label with the same name is defined and
- inside nested functions.
- A goto may jump to any visible label as long as it does not
- enter into the scope of a local variable.
- <p>
- Labels and empty statements are called <em>void statements</em>,
- as they perform no actions.
- <p>
- The <b>break</b> statement terminates the execution of a
- <b>while</b>, <b>repeat</b>, or <b>for</b> loop,
- skipping to the next statement after the loop:
- <pre>
- stat ::= <b>break</b>
- </pre><p>
- A <b>break</b> ends the innermost enclosing loop.
- <p>
- The <b>return</b> statement is used to return values
- from a function or a chunk (which is a function in disguise).
- Functions can return more than one value,
- so the syntax for the <b>return</b> statement is
- <pre>
- stat ::= <b>return</b> [explist] [‘<b>;</b>’]
- </pre>
- <p>
- The <b>return</b> statement can only be written
- as the last statement of a block.
- If it is really necessary to <b>return</b> in the middle of a block,
- then an explicit inner block can be used,
- as in the idiom <code>do return end</code>,
- because now <b>return</b> is the last statement in its (inner) block.
- <h3>3.3.5 – <a name="3.3.5">For Statement</a></h3>
- <p>
- The <b>for</b> statement has two forms:
- one numeric and one generic.
- <p>
- The numeric <b>for</b> loop repeats a block of code while a
- control variable runs through an arithmetic progression.
- It has the following syntax:
- <pre>
- stat ::= <b>for</b> Name ‘<b>=</b>’ exp ‘<b>,</b>’ exp [‘<b>,</b>’ exp] <b>do</b> block <b>end</b>
- </pre><p>
- The <em>block</em> is repeated for <em>name</em> starting at the value of
- the first <em>exp</em>, until it passes the second <em>exp</em> by steps of the
- third <em>exp</em>.
- More precisely, a <b>for</b> statement like
- <pre>
- for v = <em>e1</em>, <em>e2</em>, <em>e3</em> do <em>block</em> end
- </pre><p>
- is equivalent to the code:
- <pre>
- do
- local <em>var</em>, <em>limit</em>, <em>step</em> = tonumber(<em>e1</em>), tonumber(<em>e2</em>), tonumber(<em>e3</em>)
- if not (<em>var</em> and <em>limit</em> and <em>step</em>) then error() end
- while (<em>step</em> > 0 and <em>var</em> <= <em>limit</em>) or (<em>step</em> <= 0 and <em>var</em> >= <em>limit</em>) do
- local v = <em>var</em>
- <em>block</em>
- <em>var</em> = <em>var</em> + <em>step</em>
- end
- end
- </pre><p>
- Note the following:
- <ul>
- <li>
- All three control expressions are evaluated only once,
- before the loop starts.
- They must all result in numbers.
- </li>
- <li>
- <code><em>var</em></code>, <code><em>limit</em></code>, and <code><em>step</em></code> are invisible variables.
- The names shown here are for explanatory purposes only.
- </li>
- <li>
- If the third expression (the step) is absent,
- then a step of 1 is used.
- </li>
- <li>
- You can use <b>break</b> to exit a <b>for</b> loop.
- </li>
- <li>
- The loop variable <code>v</code> is local to the loop;
- you cannot use its value after the <b>for</b> ends or is broken.
- If you need this value,
- assign it to another variable before breaking or exiting the loop.
- </li>
- </ul>
- <p>
- The generic <b>for</b> statement works over functions,
- called <em>iterators</em>.
- On each iteration, the iterator function is called to produce a new value,
- stopping when this new value is <b>nil</b>.
- The generic <b>for</b> loop has the following syntax:
- <pre>
- stat ::= <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b>
- namelist ::= Name {‘<b>,</b>’ Name}
- </pre><p>
- A <b>for</b> statement like
- <pre>
- for <em>var_1</em>, ···, <em>var_n</em> in <em>explist</em> do <em>block</em> end
- </pre><p>
- is equivalent to the code:
- <pre>
- do
- local <em>f</em>, <em>s</em>, <em>var</em> = <em>explist</em>
- while true do
- local <em>var_1</em>, ···, <em>var_n</em> = <em>f</em>(<em>s</em>, <em>var</em>)
- if <em>var_1</em> == nil then break end
- <em>var</em> = <em>var_1</em>
- <em>block</em>
- end
- end
- </pre><p>
- Note the following:
- <ul>
- <li>
- <code><em>explist</em></code> is evaluated only once.
- Its results are an <em>iterator</em> function,
- a <em>state</em>,
- and an initial value for the first <em>iterator variable</em>.
- </li>
- <li>
- <code><em>f</em></code>, <code><em>s</em></code>, and <code><em>var</em></code> are invisible variables.
- The names are here for explanatory purposes only.
- </li>
- <li>
- You can use <b>break</b> to exit a <b>for</b> loop.
- </li>
- <li>
- The loop variables <code><em>var_i</em></code> are local to the loop;
- you cannot use their values after the <b>for</b> ends.
- If you need these values,
- then assign them to other variables before breaking or exiting the loop.
- </li>
- </ul>
- <h3>3.3.6 – <a name="3.3.6">Function Calls as Statements</a></h3><p>
- To allow possible side-effects,
- function calls can be executed as statements:
- <pre>
- stat ::= functioncall
- </pre><p>
- In this case, all returned values are thrown away.
- Function calls are explained in <a href="#3.4.9">§3.4.9</a>.
- <h3>3.3.7 – <a name="3.3.7">Local Declarations</a></h3><p>
- Local variables can be declared anywhere inside a block.
- The declaration can include an initial assignment:
- <pre>
- stat ::= <b>local</b> namelist [‘<b>=</b>’ explist]
- </pre><p>
- If present, an initial assignment has the same semantics
- of a multiple assignment (see <a href="#3.3.3">§3.3.3</a>).
- Otherwise, all variables are initialized with <b>nil</b>.
- <p>
- A chunk is also a block (see <a href="#3.3.2">§3.3.2</a>),
- and so local variables can be declared in a chunk outside any explicit block.
- <p>
- The visibility rules for local variables are explained in <a href="#3.5">§3.5</a>.
- <h2>3.4 – <a name="3.4">Expressions</a></h2>
- <p>
- The basic expressions in Lua are the following:
- <pre>
- exp ::= prefixexp
- exp ::= <b>nil</b> | <b>false</b> | <b>true</b>
- exp ::= Number
- exp ::= String
- exp ::= functiondef
- exp ::= tableconstructor
- exp ::= ‘<b>...</b>’
- exp ::= exp binop exp
- exp ::= unop exp
- prefixexp ::= var | functioncall | ‘<b>(</b>’ exp ‘<b>)</b>’
- </pre>
- <p>
- Numbers and literal strings are explained in <a href="#3.1">§3.1</a>;
- variables are explained in <a href="#3.2">§3.2</a>;
- function definitions are explained in <a href="#3.4.10">§3.4.10</a>;
- function calls are explained in <a href="#3.4.9">§3.4.9</a>;
- table constructors are explained in <a href="#3.4.8">§3.4.8</a>.
- Vararg expressions,
- denoted by three dots ('<code>...</code>'), can only be used when
- directly inside a vararg function;
- they are explained in <a href="#3.4.10">§3.4.10</a>.
- <p>
- Binary operators comprise arithmetic operators (see <a href="#3.4.1">§3.4.1</a>),
- relational operators (see <a href="#3.4.3">§3.4.3</a>), logical operators (see <a href="#3.4.4">§3.4.4</a>),
- and the concatenation operator (see <a href="#3.4.5">§3.4.5</a>).
- Unary operators comprise the unary minus (see <a href="#3.4.1">§3.4.1</a>),
- the unary <b>not</b> (see <a href="#3.4.4">§3.4.4</a>),
- and the unary <em>length operator</em> (see <a href="#3.4.6">§3.4.6</a>).
- <p>
- Both function calls and vararg expressions can result in multiple values.
- If a function call is used as a statement (see <a href="#3.3.6">§3.3.6</a>),
- then its return list is adjusted to zero elements,
- thus discarding all returned values.
- If an expression is used as the last (or the only) element
- of a list of expressions,
- then no adjustment is made
- (unless the expression is enclosed in parentheses).
- In all other contexts,
- Lua adjusts the result list to one element,
- either discarding all values except the first one
- or adding a single <b>nil</b> if there are no values.
- <p>
- Here are some examples:
- <pre>
- f() -- adjusted to 0 results
- g(f(), x) -- f() is adjusted to 1 result
- g(x, f()) -- g gets x plus all results from f()
- a,b,c = f(), x -- f() is adjusted to 1 result (c gets nil)
- a,b = ... -- a gets the first vararg parameter, b gets
- -- the second (both a and b can get nil if there
- -- is no corresponding vararg parameter)
-
- a,b,c = x, f() -- f() is adjusted to 2 results
- a,b,c = f() -- f() is adjusted to 3 results
- return f() -- returns all results from f()
- return ... -- returns all received vararg parameters
- return x,y,f() -- returns x, y, and all results from f()
- {f()} -- creates a list with all results from f()
- {...} -- creates a list with all vararg parameters
- {f(), nil} -- f() is adjusted to 1 result
- </pre>
- <p>
- Any expression enclosed in parentheses always results in only one value.
- Thus,
- <code>(f(x,y,z))</code> is always a single value,
- even if <code>f</code> returns several values.
- (The value of <code>(f(x,y,z))</code> is the first value returned by <code>f</code>
- or <b>nil</b> if <code>f</code> does not return any values.)
- <h3>3.4.1 – <a name="3.4.1">Arithmetic Operators</a></h3><p>
- Lua supports the usual arithmetic operators:
- the binary <code>+</code> (addition),
- <code>-</code> (subtraction), <code>*</code> (multiplication),
- <code>/</code> (division), <code>%</code> (modulo), and <code>^</code> (exponentiation);
- and unary <code>-</code> (mathematical negation).
- If the operands are numbers, or strings that can be converted to
- numbers (see <a href="#3.4.2">§3.4.2</a>),
- then all operations have the usual meaning.
- Exponentiation works for any exponent.
- For instance, <code>x^(-0.5)</code> computes the inverse of the square root of <code>x</code>.
- Modulo is defined as
- <pre>
- a % b == a - math.floor(a/b)*b
- </pre><p>
- That is, it is the remainder of a division that rounds
- the quotient towards minus infinity.
- <h3>3.4.2 – <a name="3.4.2">Coercion</a></h3>
- <p>
- Lua provides automatic conversion between
- string and number values at run time.
- Any arithmetic operation applied to a string tries to convert
- this string to a number, following the rules of the Lua lexer.
- (The string may have leading and trailing spaces and a sign.)
- Conversely, whenever a number is used where a string is expected,
- the number is converted to a string, in a reasonable format.
- For complete control over how numbers are converted to strings,
- use the <code>format</code> function from the string library
- (see <a href="#pdf-string.format"><code>string.format</code></a>).
- <h3>3.4.3 – <a name="3.4.3">Relational Operators</a></h3><p>
- The relational operators in Lua are
- <pre>
- == ~= < > <= >=
- </pre><p>
- These operators always result in <b>false</b> or <b>true</b>.
- <p>
- Equality (<code>==</code>) first compares the type of its operands.
- If the types are different, then the result is <b>false</b>.
- Otherwise, the values of the operands are compared.
- Numbers and strings are compared in the usual way.
- Tables, userdata, and threads
- are compared by reference:
- two objects are considered equal only if they are the same object.
- Every time you create a new object
- (a table, userdata, or thread),
- this new object is different from any previously existing object.
- Closures with the same reference are always equal.
- Closures with any detectable difference
- (different behavior, different definition) are always different.
- <p>
- You can change the way that Lua compares tables and userdata
- by using the "eq" metamethod (see <a href="#2.4">§2.4</a>).
- <p>
- The conversion rules of <a href="#3.4.2">§3.4.2</a>
- do not apply to equality comparisons.
- Thus, <code>"0"==0</code> evaluates to <b>false</b>,
- and <code>t[0]</code> and <code>t["0"]</code> denote different
- entries in a table.
- <p>
- The operator <code>~=</code> is exactly the negation of equality (<code>==</code>).
- <p>
- The order operators work as follows.
- If both arguments are numbers, then they are compared as such.
- Otherwise, if both arguments are strings,
- then their values are compared according to the current locale.
- Otherwise, Lua tries to call the "lt" or the "le"
- metamethod (see <a href="#2.4">§2.4</a>).
- A comparison <code>a > b</code> is translated to <code>b < a</code>
- and <code>a >= b</code> is translated to <code>b <= a</code>.
- <h3>3.4.4 – <a name="3.4.4">Logical Operators</a></h3><p>
- The logical operators in Lua are
- <b>and</b>, <b>or</b>, and <b>not</b>.
- Like the control structures (see <a href="#3.3.4">§3.3.4</a>),
- all logical operators consider both <b>false</b> and <b>nil</b> as false
- and anything else as true.
- <p>
- The negation operator <b>not</b> always returns <b>false</b> or <b>true</b>.
- The conjunction operator <b>and</b> returns its first argument
- if this value is <b>false</b> or <b>nil</b>;
- otherwise, <b>and</b> returns its second argument.
- The disjunction operator <b>or</b> returns its first argument
- if this value is different from <b>nil</b> and <b>false</b>;
- otherwise, <b>or</b> returns its second argument.
- Both <b>and</b> and <b>or</b> use short-cut evaluation;
- that is,
- the second operand is evaluated only if necessary.
- Here are some examples:
- <pre>
- 10 or 20 --> 10
- 10 or error() --> 10
- nil or "a" --> "a"
- nil and 10 --> nil
- false and error() --> false
- false and nil --> false
- false or nil --> nil
- 10 and 20 --> 20
- </pre><p>
- (In this manual,
- <code>--></code> indicates the result of the preceding expression.)
- <h3>3.4.5 – <a name="3.4.5">Concatenation</a></h3><p>
- The string concatenation operator in Lua is
- denoted by two dots ('<code>..</code>').
- If both operands are strings or numbers, then they are converted to
- strings according to the rules mentioned in <a href="#3.4.2">§3.4.2</a>.
- Otherwise, the <code>__concat</code> metamethod is called (see <a href="#2.4">§2.4</a>).
- <h3>3.4.6 – <a name="3.4.6">The Length Operator</a></h3>
- <p>
- The length operator is denoted by the unary prefix operator <code>#</code>.
- The length of a string is its number of bytes
- (that is, the usual meaning of string length when each
- character is one byte).
- <p>
- A program can modify the behavior of the length operator for
- any value but strings through the <code>__len</code> metamethod (see <a href="#2.4">§2.4</a>).
- <p>
- Unless a <code>__len</code> metamethod is given,
- the length of a table <code>t</code> is only defined if the
- table is a <em>sequence</em>,
- that is,
- the set of its positive numeric keys is equal to <em>{1..n}</em>
- for some non-negative integer <em>n</em>.
- In that case, <em>n</em> is its length.
- Note that a table like
- <pre>
- {10, 20, nil, 40}
- </pre><p>
- is not a sequence, because it has the key <code>4</code>
- but does not have the key <code>3</code>.
- (So, there is no <em>n</em> such that the set <em>{1..n}</em> is equal
- to the set of positive numeric keys of that table.)
- Note, however, that non-numeric keys do not interfere
- with whether a table is a sequence.
- <h3>3.4.7 – <a name="3.4.7">Precedence</a></h3><p>
- Operator precedence in Lua follows the table below,
- from lower to higher priority:
- <pre>
- or
- and
- < > <= >= ~= ==
- ..
- + -
- * / %
- not # - (unary)
- ^
- </pre><p>
- As usual,
- you can use parentheses to change the precedences of an expression.
- The concatenation ('<code>..</code>') and exponentiation ('<code>^</code>')
- operators are right associative.
- All other binary operators are left associative.
- <h3>3.4.8 – <a name="3.4.8">Table Constructors</a></h3><p>
- Table constructors are expressions that create tables.
- Every time a constructor is evaluated, a new table is created.
- A constructor can be used to create an empty table
- or to create a table and initialize some of its fields.
- The general syntax for constructors is
- <pre>
- tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’
- fieldlist ::= field {fieldsep field} [fieldsep]
- field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp | Name ‘<b>=</b>’ exp | exp
- fieldsep ::= ‘<b>,</b>’ | ‘<b>;</b>’
- </pre>
- <p>
- Each field of the form <code>[exp1] = exp2</code> adds to the new table an entry
- with key <code>exp1</code> and value <code>exp2</code>.
- A field of the form <code>name = exp</code> is equivalent to
- <code>["name"] = exp</code>.
- Finally, fields of the form <code>exp</code> are equivalent to
- <code>[i] = exp</code>, where <code>i</code> are consecutive numerical integers,
- starting with 1.
- Fields in the other formats do not affect this counting.
- For example,
- <pre>
- a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 }
- </pre><p>
- is equivalent to
- <pre>
- do
- local t = {}
- t[f(1)] = g
- t[1] = "x" -- 1st exp
- t[2] = "y" -- 2nd exp
- t.x = 1 -- t["x"] = 1
- t[3] = f(x) -- 3rd exp
- t[30] = 23
- t[4] = 45 -- 4th exp
- a = t
- end
- </pre>
- <p>
- If the last field in the list has the form <code>exp</code>
- and the expression is a function call or a vararg expression,
- then all values returned by this expression enter the list consecutively
- (see <a href="#3.4.9">§3.4.9</a>).
- <p>
- The field list can have an optional trailing separator,
- as a convenience for machine-generated code.
- <h3>3.4.9 – <a name="3.4.9">Function Calls</a></h3><p>
- A function call in Lua has the following syntax:
- <pre>
- functioncall ::= prefixexp args
- </pre><p>
- In a function call,
- first prefixexp and args are evaluated.
- If the value of prefixexp has type <em>function</em>,
- then this function is called
- with the given arguments.
- Otherwise, the prefixexp "call" metamethod is called,
- having as first parameter the value of prefixexp,
- followed by the original call arguments
- (see <a href="#2.4">§2.4</a>).
- <p>
- The form
- <pre>
- functioncall ::= prefixexp ‘<b>:</b>’ Name args
- </pre><p>
- can be used to call "methods".
- A call <code>v:name(<em>args</em>)</code>
- is syntactic sugar for <code>v.name(v,<em>args</em>)</code>,
- except that <code>v</code> is evaluated only once.
- <p>
- Arguments have the following syntax:
- <pre>
- args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’
- args ::= tableconstructor
- args ::= String
- </pre><p>
- All argument expressions are evaluated before the call.
- A call of the form <code>f{<em>fields</em>}</code> is
- syntactic sugar for <code>f({<em>fields</em>})</code>;
- that is, the argument list is a single new table.
- A call of the form <code>f'<em>string</em>'</code>
- (or <code>f"<em>string</em>"</code> or <code>f[[<em>string</em>]]</code>)
- is syntactic sugar for <code>f('<em>string</em>')</code>;
- that is, the argument list is a single literal string.
- <p>
- A call of the form <code>return <em>functioncall</em></code> is called
- a <em>tail call</em>.
- Lua implements <em>proper tail calls</em>
- (or <em>proper tail recursion</em>):
- in a tail call,
- the called function reuses the stack entry of the calling function.
- Therefore, there is no limit on the number of nested tail calls that
- a program can execute.
- However, a tail call erases any debug information about the
- calling function.
- Note that a tail call only happens with a particular syntax,
- where the <b>return</b> has one single function call as argument;
- this syntax makes the calling function return exactly
- the returns of the called function.
- So, none of the following examples are tail calls:
- <pre>
- return (f(x)) -- results adjusted to 1
- return 2 * f(x)
- return x, f(x) -- additional results
- f(x); return -- results discarded
- return x or f(x) -- results adjusted to 1
- </pre>
- <h3>3.4.10 – <a name="3.4.10">Function Definitions</a></h3>
- <p>
- The syntax for function definition is
- <pre>
- functiondef ::= <b>function</b> funcbody
- funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b>
- </pre>
- <p>
- The following syntactic sugar simplifies function definitions:
- <pre>
- stat ::= <b>function</b> funcname funcbody
- stat ::= <b>local</b> <b>function</b> Name funcbody
- funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name]
- </pre><p>
- The statement
- <pre>
- function f () <em>body</em> end
- </pre><p>
- translates to
- <pre>
- f = function () <em>body</em> end
- </pre><p>
- The statement
- <pre>
- function t.a.b.c.f () <em>body</em> end
- </pre><p>
- translates to
- <pre>
- t.a.b.c.f = function () <em>body</em> end
- </pre><p>
- The statement
- <pre>
- local function f () <em>body</em> end
- </pre><p>
- translates to
- <pre>
- local f; f = function () <em>body</em> end
- </pre><p>
- not to
- <pre>
- local f = function () <em>body</em> end
- </pre><p>
- (This only makes a difference when the body of the function
- contains references to <code>f</code>.)
- <p>
- A function definition is an executable expression,
- whose value has type <em>function</em>.
- When Lua precompiles a chunk,
- all its function bodies are precompiled too.
- Then, whenever Lua executes the function definition,
- the function is <em>instantiated</em> (or <em>closed</em>).
- This function instance (or <em>closure</em>)
- is the final value of the expression.
- <p>
- Parameters act as local variables that are
- initialized with the argument values:
- <pre>
- parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] | ‘<b>...</b>’
- </pre><p>
- When a function is called,
- the list of arguments is adjusted to
- the length of the list of parameters,
- unless the function is a <em>vararg function</em>,
- which is indicated by three dots ('<code>...</code>')
- at the end of its parameter list.
- A vararg function does not adjust its argument list;
- instead, it collects all extra arguments and supplies them
- to the function through a <em>vararg expression</em>,
- which is also written as three dots.
- The value of this expression is a list of all actual extra arguments,
- similar to a function with multiple results.
- If a vararg expression is used inside another expression
- or in the middle of a list of expressions,
- then its return list is adjusted to one element.
- If the expression is used as the last element of a list of expressions,
- then no adjustment is made
- (unless that last expression is enclosed in parentheses).
- <p>
- As an example, consider the following definitions:
- <pre>
- function f(a, b) end
- function g(a, b, ...) end
- function r() return 1,2,3 end
- </pre><p>
- Then, we have the following mapping from arguments to parameters and
- to the vararg expression:
- <pre>
- CALL PARAMETERS
-
- f(3) a=3, b=nil
- f(3, 4) a=3, b=4
- f(3, 4, 5) a=3, b=4
- f(r(), 10) a=1, b=10
- f(r()) a=1, b=2
-
- g(3) a=3, b=nil, ... --> (nothing)
- g(3, 4) a=3, b=4, ... --> (nothing)
- g(3, 4, 5, 8) a=3, b=4, ... --> 5 8
- g(5, r()) a=5, b=1, ... --> 2 3
- </pre>
- <p>
- Results are returned using the <b>return</b> statement (see <a href="#3.3.4">§3.3.4</a>).
- If control reaches the end of a function
- without encountering a <b>return</b> statement,
- then the function returns with no results.
- <p>
- There is a system-dependent limit on the number of values
- that a function may return.
- This limit is guaranteed to be larger than 1000.
- <p>
- The <em>colon</em> syntax
- is used for defining <em>methods</em>,
- that is, functions that have an implicit extra parameter <code>self</code>.
- Thus, the statement
- <pre>
- function t.a.b.c:f (<em>params</em>) <em>body</em> end
- </pre><p>
- is syntactic sugar for
- <pre>
- t.a.b.c.f = function (self, <em>params</em>) <em>body</em> end
- </pre>
- <h2>3.5 – <a name="3.5">Visibility Rules</a></h2>
- <p>
- Lua is a lexically scoped language.
- The scope of a local variable begins at the first statement after
- its declaration and lasts until the last non-void statement
- of the innermost block that includes the declaration.
- Consider the following example:
- <pre>
- x = 10 -- global variable
- do -- new block
- local x = x -- new 'x', with value 10
- print(x) --> 10
- x = x+1
- do -- another block
- local x = x+1 -- another 'x'
- print(x) --> 12
- end
- print(x) --> 11
- end
- print(x) --> 10 (the global one)
- </pre>
- <p>
- Notice that, in a declaration like <code>local x = x</code>,
- the new <code>x</code> being declared is not in scope yet,
- and so the second <code>x</code> refers to the outside variable.
- <p>
- Because of the lexical scoping rules,
- local variables can be freely accessed by functions
- defined inside their scope.
- A local variable used by an inner function is called
- an <em>upvalue</em>, or <em>external local variable</em>,
- inside the inner function.
- <p>
- Notice that each execution of a <b>local</b> statement
- defines new local variables.
- Consider the following example:
- <pre>
- a = {}
- local x = 20
- for i=1,10 do
- local y = 0
- a[i] = function () y=y+1; return x+y end
- end
- </pre><p>
- The loop creates ten closures
- (that is, ten instances of the anonymous function).
- Each of these closures uses a different <code>y</code> variable,
- while all of them share the same <code>x</code>.
- <h1>4 – <a name="4">The Application Program Interface</a></h1>
- <p>
- This section describes the C API for Lua, that is,
- the set of C functions available to the host program to communicate
- with Lua.
- All API functions and related types and constants
- are declared in the header file <a name="pdf-lua.h"><code>lua.h</code></a>.
- <p>
- Even when we use the term "function",
- any facility in the API may be provided as a macro instead.
- Except where stated otherwise,
- all such macros use each of their arguments exactly once
- (except for the first argument, which is always a Lua state),
- and so do not generate any hidden side-effects.
- <p>
- As in most C libraries,
- the Lua API functions do not check their arguments for validity or consistency.
- However, you can change this behavior by compiling Lua
- with the macro <a name="pdf-LUA_USE_APICHECK"><code>LUA_USE_APICHECK</code></a> defined.
- <h2>4.1 – <a name="4.1">The Stack</a></h2>
- <p>
- Lua uses a <em>virtual stack</em> to pass values to and from C.
- Each element in this stack represents a Lua value
- (<b>nil</b>, number, string, etc.).
- <p>
- Whenever Lua calls C, the called function gets a new stack,
- which is independent of previous stacks and of stacks of
- C functions that are still active.
- This stack initially contains any arguments to the C function
- and it is where the C function pushes its results
- to be returned to the caller (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
- <p>
- For convenience,
- most query operations in the API do not follow a strict stack discipline.
- Instead, they can refer to any element in the stack
- by using an <em>index</em>:
- A positive index represents an absolute stack position
- (starting at 1);
- a negative index represents an offset relative to the top of the stack.
- More specifically, if the stack has <em>n</em> elements,
- then index 1 represents the first element
- (that is, the element that was pushed onto the stack first)
- and
- index <em>n</em> represents the last element;
- index -1 also represents the last element
- (that is, the element at the top)
- and index <em>-n</em> represents the first element.
- <h2>4.2 – <a name="4.2">Stack Size</a></h2>
- <p>
- When you interact with the Lua API,
- you are responsible for ensuring consistency.
- In particular,
- <em>you are responsible for controlling stack overflow</em>.
- You can use the function <a href="#lua_checkstack"><code>lua_checkstack</code></a>
- to ensure that the stack has extra slots when pushing new elements.
- <p>
- Whenever Lua calls C,
- it ensures that the stack has at least <a name="pdf-LUA_MINSTACK"><code>LUA_MINSTACK</code></a> extra slots.
- <code>LUA_MINSTACK</code> is defined as 20,
- so that usually you do not have to worry about stack space
- unless your code has loops pushing elements onto the stack.
- <p>
- When you call a Lua function
- without a fixed number of results (see <a href="#lua_call"><code>lua_call</code></a>),
- Lua ensures that the stack has enough size for all results,
- but it does not ensure any extra space.
- So, before pushing anything in the stack after such a call
- you should use <a href="#lua_checkstack"><code>lua_checkstack</code></a>.
- <h2>4.3 – <a name="4.3">Valid and Acceptable Indices</a></h2>
- <p>
- Any function in the API that receives stack indices
- works only with <em>valid indices</em> or <em>acceptable indices</em>.
- <p>
- A <em>valid index</em> is an index that refers to a
- real position within the stack, that is,
- its position lies between 1 and the stack top
- (<code>1 ≤ abs(index) ≤ top</code>).
- Usually, functions that can modify the value at an index
- require valid indices.
- <p>
- Unless otherwise noted,
- any function that accepts valid indices also accepts <em>pseudo-indices</em>,
- which represent some Lua values that are accessible to C code
- but which are not in the stack.
- Pseudo-indices are used to access the registry
- and the upvalues of a C function (see <a href="#4.4">§4.4</a>).
- <p>
- Functions that do not need a specific stack position,
- but only a value in the stack (e.g., query functions),
- can be called with acceptable indices.
- An <em>acceptable index</em> can be any valid index,
- including the pseudo-indices,
- but it also can be any positive index after the stack top
- within the space allocated for the stack,
- that is, indices up to the stack size.
- (Note that 0 is never an acceptable index.)
- Except when noted otherwise,
- functions in the API work with acceptable indices.
- <p>
- Acceptable indices serve to avoid extra tests
- against the stack top when querying the stack.
- For instance, a C function can query its third argument
- without the need to first check whether there is a third argument,
- that is, without the need to check whether 3 is a valid index.
- <p>
- For functions that can be called with acceptable indices,
- any non-valid index is treated as if it
- contains a value of a virtual type <a name="pdf-LUA_TNONE"><code>LUA_TNONE</code></a>,
- which behaves like a nil value.
- <h2>4.4 – <a name="4.4">C Closures</a></h2>
- <p>
- When a C function is created,
- it is possible to associate some values with it,
- thus creating a <em>C closure</em>
- (see <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>);
- these values are called <em>upvalues</em> and are
- accessible to the function whenever it is called.
- <p>
- Whenever a C function is called,
- its upvalues are located at specific pseudo-indices.
- These pseudo-indices are produced by the macro
- <a href="#lua_upvalueindex"><code>lua_upvalueindex</code></a>.
- The first value associated with a function is at position
- <code>lua_upvalueindex(1)</code>, and so on.
- Any access to <code>lua_upvalueindex(<em>n</em>)</code>,
- where <em>n</em> is greater than the number of upvalues of the
- current function (but not greater than 256),
- produces an acceptable but invalid index.
- <h2>4.5 – <a name="4.5">Registry</a></h2>
- <p>
- Lua provides a <em>registry</em>,
- a predefined table that can be used by any C code to
- store whatever Lua values it needs to store.
- The registry table is always located at pseudo-index
- <a name="pdf-LUA_REGISTRYINDEX"><code>LUA_REGISTRYINDEX</code></a>,
- which is a valid index.
- Any C library can store data into this table,
- but it should take care to choose keys
- that are different from those used
- by other libraries, to avoid collisions.
- Typically, you should use as key a string containing your library name,
- or a light userdata with the address of a C object in your code,
- or any Lua object created by your code.
- As with global names,
- string keys starting with an underscore followed by
- uppercase letters are reserved for Lua.
- <p>
- The integer keys in the registry are used by the reference mechanism,
- implemented by the auxiliary library,
- and by some predefined values.
- Therefore, integer keys should not be used for other purposes.
- <p>
- When you create a new Lua state,
- its registry comes with some predefined values.
- These predefined values are indexed with integer keys
- defined as constants in <code>lua.h</code>.
- The following constants are defined:
- <ul>
- <li><b><a name="pdf-LUA_RIDX_MAINTHREAD"><code>LUA_RIDX_MAINTHREAD</code></a>: </b> At this index the registry has
- the main thread of the state.
- (The main thread is the one created together with the state.)
- </li>
- <li><b><a name="pdf-LUA_RIDX_GLOBALS"><code>LUA_RIDX_GLOBALS</code></a>: </b> At this index the registry has
- the global environment.
- </li>
- </ul>
- <h2>4.6 – <a name="4.6">Error Handling in C</a></h2>
- <p>
- Internally, Lua uses the C <code>longjmp</code> facility to handle errors.
- (You can also choose to use exceptions if you compile Lua as C++;
- search for <code>LUAI_THROW</code> in the source code.)
- When Lua faces any error
- (such as a memory allocation error, type errors, syntax errors,
- and runtime errors)
- it <em>raises</em> an error;
- that is, it does a long jump.
- A <em>protected environment</em> uses <code>setjmp</code>
- to set a recovery point;
- any error jumps to the most recent active recovery point.
- <p>
- If an error happens outside any protected environment,
- Lua calls a <em>panic function</em> (see <a href="#lua_atpanic"><code>lua_atpanic</code></a>)
- and then calls <code>abort</code>,
- thus exiting the host application.
- Your panic function can avoid this exit by
- never returning
- (e.g., doing a long jump to your own recovery point outside Lua).
- <p>
- The panic function runs as if it were a message handler (see <a href="#2.3">§2.3</a>);
- in particular, the error message is at the top of the stack.
- However, there is no guarantees about stack space.
- To push anything on the stack,
- the panic function should first check the available space (see <a href="#4.2">§4.2</a>).
- <p>
- Most functions in the API can throw an error,
- for instance due to a memory allocation error.
- The documentation for each function indicates whether
- it can throw errors.
- <p>
- Inside a C function you can throw an error by calling <a href="#lua_error"><code>lua_error</code></a>.
- <h2>4.7 – <a name="4.7">Handling Yields in C</a></h2>
- <p>
- Internally, Lua uses the C <code>longjmp</code> facility to yield a coroutine.
- Therefore, if a function <code>foo</code> calls an API function
- and this API function yields
- (directly or indirectly by calling another function that yields),
- Lua cannot return to <code>foo</code> any more,
- because the <code>longjmp</code> removes its frame from the C stack.
- <p>
- To avoid this kind of problem,
- Lua raises an error whenever it tries to yield across an API call,
- except for three functions:
- <a href="#lua_yieldk"><code>lua_yieldk</code></a>, <a href="#lua_callk"><code>lua_callk</code></a>, and <a href="#lua_pcallk"><code>lua_pcallk</code></a>.
- All those functions receive a <em>continuation function</em>
- (as a parameter called <code>k</code>) to continue execution after a yield.
- <p>
- We need to set some terminology to explain continuations.
- We have a C function called from Lua which we will call
- the <em>original function</em>.
- This original function then calls one of those three functions in the C API,
- which we will call the <em>callee function</em>,
- that then yields the current thread.
- (This can happen when the callee function is <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
- or when the callee function is either <a href="#lua_callk"><code>lua_callk</code></a> or <a href="#lua_pcallk"><code>lua_pcallk</code></a>
- and the function called by them yields.)
- <p>
- Suppose the running thread yields while executing the callee function.
- After the thread resumes,
- it eventually will finish running the callee function.
- However,
- the callee function cannot return to the original function,
- because its frame in the C stack was destroyed by the yield.
- Instead, Lua calls a <em>continuation function</em>,
- which was given as an argument to the callee function.
- As the name implies,
- the continuation function should continue the task
- of the original function.
- <p>
- Lua treats the continuation function as if it were the original function.
- The continuation function receives the same Lua stack
- from the original function,
- in the same state it would be if the callee function had returned.
- (For instance,
- after a <a href="#lua_callk"><code>lua_callk</code></a> the function and its arguments are
- removed from the stack and replaced by the results from the call.)
- It also has the same upvalues.
- Whatever it returns is handled by Lua as if it were the return
- of the original function.
- <p>
- The only difference in the Lua state between the original function
- and its continuation is the result of a call to <a href="#lua_getctx"><code>lua_getctx</code></a>.
- <h2>4.8 – <a name="4.8">Functions and Types</a></h2>
- <p>
- Here we list all functions and types from the C API in
- alphabetical order.
- Each function has an indicator like this:
- <span class="apii">[-o, +p, <em>x</em>]</span>
- <p>
- The first field, <code>o</code>,
- is how many elements the function pops from the stack.
- The second field, <code>p</code>,
- is how many elements the function pushes onto the stack.
- (Any function always pushes its results after popping its arguments.)
- A field in the form <code>x|y</code> means the function can push (or pop)
- <code>x</code> or <code>y</code> elements,
- depending on the situation;
- an interrogation mark '<code>?</code>' means that
- we cannot know how many elements the function pops/pushes
- by looking only at its arguments
- (e.g., they may depend on what is on the stack).
- The third field, <code>x</code>,
- tells whether the function may throw errors:
- '<code>-</code>' means the function never throws any error;
- '<code>e</code>' means the function may throw errors;
- '<code>v</code>' means the function may throw an error on purpose.
- <hr><h3><a name="lua_absindex"><code>lua_absindex</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_absindex (lua_State *L, int idx);</pre>
- <p>
- Converts the acceptable index <code>idx</code> into an absolute index
- (that is, one that does not depend on the stack top).
- <hr><h3><a name="lua_Alloc"><code>lua_Alloc</code></a></h3>
- <pre>typedef void * (*lua_Alloc) (void *ud,
- void *ptr,
- size_t osize,
- size_t nsize);</pre>
- <p>
- The type of the memory-allocation function used by Lua states.
- The allocator function must provide a
- functionality similar to <code>realloc</code>,
- but not exactly the same.
- Its arguments are
- <code>ud</code>, an opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>;
- <code>ptr</code>, a pointer to the block being allocated/reallocated/freed;
- <code>osize</code>, the original size of the block or some code about what
- is being allocated;
- <code>nsize</code>, the new size of the block.
- <p>
- When <code>ptr</code> is not <code>NULL</code>,
- <code>osize</code> is the size of the block pointed by <code>ptr</code>,
- that is, the size given when it was allocated or reallocated.
- <p>
- When <code>ptr</code> is <code>NULL</code>,
- <code>osize</code> encodes the kind of object that Lua is allocating.
- <code>osize</code> is any of
- <a href="#pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>, <a href="#pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>, <a href="#pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>,
- <a href="#pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>, or <a href="#pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a> when (and only when)
- Lua is creating a new object of that type.
- When <code>osize</code> is some other value,
- Lua is allocating memory for something else.
- <p>
- Lua assumes the following behavior from the allocator function:
- <p>
- When <code>nsize</code> is zero,
- the allocator should behave like <code>free</code>
- and return <code>NULL</code>.
- <p>
- When <code>nsize</code> is not zero,
- the allocator should behave like <code>realloc</code>.
- The allocator returns <code>NULL</code>
- if and only if it cannot fulfill the request.
- Lua assumes that the allocator never fails when
- <code>osize >= nsize</code>.
- <p>
- Here is a simple implementation for the allocator function.
- It is used in the auxiliary library by <a href="#luaL_newstate"><code>luaL_newstate</code></a>.
- <pre>
- static void *l_alloc (void *ud, void *ptr, size_t osize,
- size_t nsize) {
- (void)ud; (void)osize; /* not used */
- if (nsize == 0) {
- free(ptr);
- return NULL;
- }
- else
- return realloc(ptr, nsize);
- }
- </pre><p>
- Note that Standard C ensures
- that <code>free(NULL)</code> has no effect and that
- <code>realloc(NULL, size)</code> is equivalent to <code>malloc(size)</code>.
- This code assumes that <code>realloc</code> does not fail when shrinking a block.
- (Although Standard C does not ensure this behavior,
- it seems to be a safe assumption.)
- <hr><h3><a name="lua_arith"><code>lua_arith</code></a></h3><p>
- <span class="apii">[-(2|1), +1, <em>e</em>]</span>
- <pre>void lua_arith (lua_State *L, int op);</pre>
- <p>
- Performs an arithmetic operation over the two values
- (or one, in the case of negation)
- at the top of the stack,
- with the value at the top being the second operand,
- pops these values, and pushes the result of the operation.
- The function follows the semantics of the corresponding Lua operator
- (that is, it may call metamethods).
- <p>
- The value of <code>op</code> must be one of the following constants:
- <ul>
- <li><b><a name="pdf-LUA_OPADD"><code>LUA_OPADD</code></a>: </b> performs addition (<code>+</code>)</li>
- <li><b><a name="pdf-LUA_OPSUB"><code>LUA_OPSUB</code></a>: </b> performs subtraction (<code>-</code>)</li>
- <li><b><a name="pdf-LUA_OPMUL"><code>LUA_OPMUL</code></a>: </b> performs multiplication (<code>*</code>)</li>
- <li><b><a name="pdf-LUA_OPDIV"><code>LUA_OPDIV</code></a>: </b> performs division (<code>/</code>)</li>
- <li><b><a name="pdf-LUA_OPMOD"><code>LUA_OPMOD</code></a>: </b> performs modulo (<code>%</code>)</li>
- <li><b><a name="pdf-LUA_OPPOW"><code>LUA_OPPOW</code></a>: </b> performs exponentiation (<code>^</code>)</li>
- <li><b><a name="pdf-LUA_OPUNM"><code>LUA_OPUNM</code></a>: </b> performs mathematical negation (unary <code>-</code>)</li>
- </ul>
- <hr><h3><a name="lua_atpanic"><code>lua_atpanic</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);</pre>
- <p>
- Sets a new panic function and returns the old one (see <a href="#4.6">§4.6</a>).
- <hr><h3><a name="lua_call"><code>lua_call</code></a></h3><p>
- <span class="apii">[-(nargs+1), +nresults, <em>e</em>]</span>
- <pre>void lua_call (lua_State *L, int nargs, int nresults);</pre>
- <p>
- Calls a function.
- <p>
- To call a function you must use the following protocol:
- first, the function to be called is pushed onto the stack;
- then, the arguments to the function are pushed
- in direct order;
- that is, the first argument is pushed first.
- Finally you call <a href="#lua_call"><code>lua_call</code></a>;
- <code>nargs</code> is the number of arguments that you pushed onto the stack.
- All arguments and the function value are popped from the stack
- when the function is called.
- The function results are pushed onto the stack when the function returns.
- The number of results is adjusted to <code>nresults</code>,
- unless <code>nresults</code> is <a name="pdf-LUA_MULTRET"><code>LUA_MULTRET</code></a>.
- In this case, all results from the function are pushed.
- Lua takes care that the returned values fit into the stack space.
- The function results are pushed onto the stack in direct order
- (the first result is pushed first),
- so that after the call the last result is on the top of the stack.
- <p>
- Any error inside the called function is propagated upwards
- (with a <code>longjmp</code>).
- <p>
- The following example shows how the host program can do the
- equivalent to this Lua code:
- <pre>
- a = f("how", t.x, 14)
- </pre><p>
- Here it is in C:
- <pre>
- lua_getglobal(L, "f"); /* function to be called */
- lua_pushstring(L, "how"); /* 1st argument */
- lua_getglobal(L, "t"); /* table to be indexed */
- lua_getfield(L, -1, "x"); /* push result of t.x (2nd arg) */
- lua_remove(L, -2); /* remove 't' from the stack */
- lua_pushinteger(L, 14); /* 3rd argument */
- lua_call(L, 3, 1); /* call 'f' with 3 arguments and 1 result */
- lua_setglobal(L, "a"); /* set global 'a' */
- </pre><p>
- Note that the code above is "balanced":
- at its end, the stack is back to its original configuration.
- This is considered good programming practice.
- <hr><h3><a name="lua_callk"><code>lua_callk</code></a></h3><p>
- <span class="apii">[-(nargs + 1), +nresults, <em>e</em>]</span>
- <pre>void lua_callk (lua_State *L, int nargs, int nresults, int ctx,
- lua_CFunction k);</pre>
- <p>
- This function behaves exactly like <a href="#lua_call"><code>lua_call</code></a>,
- but allows the called function to yield (see <a href="#4.7">§4.7</a>).
- <hr><h3><a name="lua_CFunction"><code>lua_CFunction</code></a></h3>
- <pre>typedef int (*lua_CFunction) (lua_State *L);</pre>
- <p>
- Type for C functions.
- <p>
- In order to communicate properly with Lua,
- a C function must use the following protocol,
- which defines the way parameters and results are passed:
- a C function receives its arguments from Lua in its stack
- in direct order (the first argument is pushed first).
- So, when the function starts,
- <code>lua_gettop(L)</code> returns the number of arguments received by the function.
- The first argument (if any) is at index 1
- and its last argument is at index <code>lua_gettop(L)</code>.
- To return values to Lua, a C function just pushes them onto the stack,
- in direct order (the first result is pushed first),
- and returns the number of results.
- Any other value in the stack below the results will be properly
- discarded by Lua.
- Like a Lua function, a C function called by Lua can also return
- many results.
- <p>
- As an example, the following function receives a variable number
- of numerical arguments and returns their average and sum:
- <pre>
- static int foo (lua_State *L) {
- int n = lua_gettop(L); /* number of arguments */
- lua_Number sum = 0;
- int i;
- for (i = 1; i <= n; i++) {
- if (!lua_isnumber(L, i)) {
- lua_pushstring(L, "incorrect argument");
- lua_error(L);
- }
- sum += lua_tonumber(L, i);
- }
- lua_pushnumber(L, sum/n); /* first result */
- lua_pushnumber(L, sum); /* second result */
- return 2; /* number of results */
- }
- </pre>
- <hr><h3><a name="lua_checkstack"><code>lua_checkstack</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_checkstack (lua_State *L, int extra);</pre>
- <p>
- Ensures that there are at least <code>extra</code> free stack slots in the stack.
- It returns false if it cannot fulfill the request,
- because it would cause the stack to be larger than a fixed maximum size
- (typically at least a few thousand elements) or
- because it cannot allocate memory for the new stack size.
- This function never shrinks the stack;
- if the stack is already larger than the new size,
- it is left unchanged.
- <hr><h3><a name="lua_close"><code>lua_close</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void lua_close (lua_State *L);</pre>
- <p>
- Destroys all objects in the given Lua state
- (calling the corresponding garbage-collection metamethods, if any)
- and frees all dynamic memory used by this state.
- On several platforms, you may not need to call this function,
- because all resources are naturally released when the host program ends.
- On the other hand, long-running programs that create multiple states,
- such as daemons or web servers,
- might need to close states as soon as they are not needed.
- <hr><h3><a name="lua_compare"><code>lua_compare</code></a></h3><p>
- <span class="apii">[-0, +0, <em>e</em>]</span>
- <pre>int lua_compare (lua_State *L, int index1, int index2, int op);</pre>
- <p>
- Compares two Lua values.
- Returns 1 if the value at index <code>index1</code> satisfies <code>op</code>
- when compared with the value at index <code>index2</code>,
- following the semantics of the corresponding Lua operator
- (that is, it may call metamethods).
- Otherwise returns 0.
- Also returns 0 if any of the indices is non valid.
- <p>
- The value of <code>op</code> must be one of the following constants:
- <ul>
- <li><b><a name="pdf-LUA_OPEQ"><code>LUA_OPEQ</code></a>: </b> compares for equality (<code>==</code>)</li>
- <li><b><a name="pdf-LUA_OPLT"><code>LUA_OPLT</code></a>: </b> compares for less than (<code><</code>)</li>
- <li><b><a name="pdf-LUA_OPLE"><code>LUA_OPLE</code></a>: </b> compares for less or equal (<code><=</code>)</li>
- </ul>
- <hr><h3><a name="lua_concat"><code>lua_concat</code></a></h3><p>
- <span class="apii">[-n, +1, <em>e</em>]</span>
- <pre>void lua_concat (lua_State *L, int n);</pre>
- <p>
- Concatenates the <code>n</code> values at the top of the stack,
- pops them, and leaves the result at the top.
- If <code>n</code> is 1, the result is the single value on the stack
- (that is, the function does nothing);
- if <code>n</code> is 0, the result is the empty string.
- Concatenation is performed following the usual semantics of Lua
- (see <a href="#3.4.5">§3.4.5</a>).
- <hr><h3><a name="lua_copy"><code>lua_copy</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void lua_copy (lua_State *L, int fromidx, int toidx);</pre>
- <p>
- Moves the element at index <code>fromidx</code>
- into the valid index <code>toidx</code>
- without shifting any element
- (therefore replacing the value at that position).
- <hr><h3><a name="lua_createtable"><code>lua_createtable</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>void lua_createtable (lua_State *L, int narr, int nrec);</pre>
- <p>
- Creates a new empty table and pushes it onto the stack.
- Parameter <code>narr</code> is a hint for how many elements the table
- will have as a sequence;
- parameter <code>nrec</code> is a hint for how many other elements
- the table will have.
- Lua may use these hints to preallocate memory for the new table.
- This pre-allocation is useful for performance when you know in advance
- how many elements the table will have.
- Otherwise you can use the function <a href="#lua_newtable"><code>lua_newtable</code></a>.
- <hr><h3><a name="lua_dump"><code>lua_dump</code></a></h3><p>
- <span class="apii">[-0, +0, <em>e</em>]</span>
- <pre>int lua_dump (lua_State *L, lua_Writer writer, void *data);</pre>
- <p>
- Dumps a function as a binary chunk.
- Receives a Lua function on the top of the stack
- and produces a binary chunk that,
- if loaded again,
- results in a function equivalent to the one dumped.
- As it produces parts of the chunk,
- <a href="#lua_dump"><code>lua_dump</code></a> calls function <code>writer</code> (see <a href="#lua_Writer"><code>lua_Writer</code></a>)
- with the given <code>data</code>
- to write them.
- <p>
- The value returned is the error code returned by the last
- call to the writer;
- 0 means no errors.
- <p>
- This function does not pop the Lua function from the stack.
- <hr><h3><a name="lua_error"><code>lua_error</code></a></h3><p>
- <span class="apii">[-1, +0, <em>v</em>]</span>
- <pre>int lua_error (lua_State *L);</pre>
- <p>
- Generates a Lua error.
- The error message (which can actually be a Lua value of any type)
- must be on the stack top.
- This function does a long jump,
- and therefore never returns
- (see <a href="#luaL_error"><code>luaL_error</code></a>).
- <hr><h3><a name="lua_gc"><code>lua_gc</code></a></h3><p>
- <span class="apii">[-0, +0, <em>e</em>]</span>
- <pre>int lua_gc (lua_State *L, int what, int data);</pre>
- <p>
- Controls the garbage collector.
- <p>
- This function performs several tasks,
- according to the value of the parameter <code>what</code>:
- <ul>
- <li><b><code>LUA_GCSTOP</code>: </b>
- stops the garbage collector.
- </li>
- <li><b><code>LUA_GCRESTART</code>: </b>
- restarts the garbage collector.
- </li>
- <li><b><code>LUA_GCCOLLECT</code>: </b>
- performs a full garbage-collection cycle.
- </li>
- <li><b><code>LUA_GCCOUNT</code>: </b>
- returns the current amount of memory (in Kbytes) in use by Lua.
- </li>
- <li><b><code>LUA_GCCOUNTB</code>: </b>
- returns the remainder of dividing the current amount of bytes of
- memory in use by Lua by 1024.
- </li>
- <li><b><code>LUA_GCSTEP</code>: </b>
- performs an incremental step of garbage collection.
- The step "size" is controlled by <code>data</code>
- (larger values mean more steps) in a non-specified way.
- If you want to control the step size
- you must experimentally tune the value of <code>data</code>.
- The function returns 1 if the step finished a
- garbage-collection cycle.
- </li>
- <li><b><code>LUA_GCSETPAUSE</code>: </b>
- sets <code>data</code> as the new value
- for the <em>pause</em> of the collector (see <a href="#2.5">§2.5</a>).
- The function returns the previous value of the pause.
- </li>
- <li><b><code>LUA_GCSETSTEPMUL</code>: </b>
- sets <code>data</code> as the new value for the <em>step multiplier</em> of
- the collector (see <a href="#2.5">§2.5</a>).
- The function returns the previous value of the step multiplier.
- </li>
- <li><b><code>LUA_GCISRUNNING</code>: </b>
- returns a boolean that tells whether the collector is running
- (i.e., not stopped).
- </li>
- <li><b><code>LUA_GCGEN</code>: </b>
- changes the collector to generational mode
- (see <a href="#2.5">§2.5</a>).
- </li>
- <li><b><code>LUA_GCINC</code>: </b>
- changes the collector to incremental mode.
- This is the default mode.
- </li>
- </ul>
- <p>
- For more details about these options,
- see <a href="#pdf-collectgarbage"><code>collectgarbage</code></a>.
- <hr><h3><a name="lua_getallocf"><code>lua_getallocf</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Alloc lua_getallocf (lua_State *L, void **ud);</pre>
- <p>
- Returns the memory-allocation function of a given state.
- If <code>ud</code> is not <code>NULL</code>, Lua stores in <code>*ud</code> the
- opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>.
- <hr><h3><a name="lua_getctx"><code>lua_getctx</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_getctx (lua_State *L, int *ctx);</pre>
- <p>
- This function is called by a continuation function (see <a href="#4.7">§4.7</a>)
- to retrieve the status of the thread and a context information.
- <p>
- When called in the original function,
- <a href="#lua_getctx"><code>lua_getctx</code></a> always returns <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>
- and does not change the value of its argument <code>ctx</code>.
- When called inside a continuation function,
- <a href="#lua_getctx"><code>lua_getctx</code></a> returns <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> and sets
- the value of <code>ctx</code> to be the context information
- (the value passed as the <code>ctx</code> argument
- to the callee together with the continuation function).
- <p>
- When the callee is <a href="#lua_pcallk"><code>lua_pcallk</code></a>,
- Lua may also call its continuation function
- to handle errors during the call.
- That is, upon an error in the function called by <a href="#lua_pcallk"><code>lua_pcallk</code></a>,
- Lua may not return to the original function
- but instead may call the continuation function.
- In that case, a call to <a href="#lua_getctx"><code>lua_getctx</code></a> will return the error code
- (the value that would be returned by <a href="#lua_pcallk"><code>lua_pcallk</code></a>);
- the value of <code>ctx</code> will be set to the context information,
- as in the case of a yield.
- <hr><h3><a name="lua_getfield"><code>lua_getfield</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>void lua_getfield (lua_State *L, int index, const char *k);</pre>
- <p>
- Pushes onto the stack the value <code>t[k]</code>,
- where <code>t</code> is the value at the given index.
- As in Lua, this function may trigger a metamethod
- for the "index" event (see <a href="#2.4">§2.4</a>).
- <hr><h3><a name="lua_getglobal"><code>lua_getglobal</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>void lua_getglobal (lua_State *L, const char *name);</pre>
- <p>
- Pushes onto the stack the value of the global <code>name</code>.
- <hr><h3><a name="lua_getmetatable"><code>lua_getmetatable</code></a></h3><p>
- <span class="apii">[-0, +(0|1), –]</span>
- <pre>int lua_getmetatable (lua_State *L, int index);</pre>
- <p>
- Pushes onto the stack the metatable of the value at the given index.
- If the value does not have a metatable,
- the function returns 0 and pushes nothing on the stack.
- <hr><h3><a name="lua_gettable"><code>lua_gettable</code></a></h3><p>
- <span class="apii">[-1, +1, <em>e</em>]</span>
- <pre>void lua_gettable (lua_State *L, int index);</pre>
- <p>
- Pushes onto the stack the value <code>t[k]</code>,
- where <code>t</code> is the value at the given index
- and <code>k</code> is the value at the top of the stack.
- <p>
- This function pops the key from the stack
- (putting the resulting value in its place).
- As in Lua, this function may trigger a metamethod
- for the "index" event (see <a href="#2.4">§2.4</a>).
- <hr><h3><a name="lua_gettop"><code>lua_gettop</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_gettop (lua_State *L);</pre>
- <p>
- Returns the index of the top element in the stack.
- Because indices start at 1,
- this result is equal to the number of elements in the stack
- (and so 0 means an empty stack).
- <hr><h3><a name="lua_getuservalue"><code>lua_getuservalue</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_getuservalue (lua_State *L, int index);</pre>
- <p>
- Pushes onto the stack the Lua value associated with the userdata
- at the given index.
- This Lua value must be a table or <b>nil</b>.
- <hr><h3><a name="lua_insert"><code>lua_insert</code></a></h3><p>
- <span class="apii">[-1, +1, –]</span>
- <pre>void lua_insert (lua_State *L, int index);</pre>
- <p>
- Moves the top element into the given valid index,
- shifting up the elements above this index to open space.
- This function cannot be called with a pseudo-index,
- because a pseudo-index is not an actual stack position.
- <hr><h3><a name="lua_Integer"><code>lua_Integer</code></a></h3>
- <pre>typedef ptrdiff_t lua_Integer;</pre>
- <p>
- The type used by the Lua API to represent signed integral values.
- <p>
- By default it is a <code>ptrdiff_t</code>,
- which is usually the largest signed integral type the machine handles
- "comfortably".
- <hr><h3><a name="lua_isboolean"><code>lua_isboolean</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isboolean (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a boolean,
- and 0 otherwise.
- <hr><h3><a name="lua_iscfunction"><code>lua_iscfunction</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_iscfunction (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a C function,
- and 0 otherwise.
- <hr><h3><a name="lua_isfunction"><code>lua_isfunction</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isfunction (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a function
- (either C or Lua), and 0 otherwise.
- <hr><h3><a name="lua_islightuserdata"><code>lua_islightuserdata</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_islightuserdata (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a light userdata,
- and 0 otherwise.
- <hr><h3><a name="lua_isnil"><code>lua_isnil</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isnil (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is <b>nil</b>,
- and 0 otherwise.
- <hr><h3><a name="lua_isnone"><code>lua_isnone</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isnone (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the given index is not valid,
- and 0 otherwise.
- <hr><h3><a name="lua_isnoneornil"><code>lua_isnoneornil</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isnoneornil (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the given index is not valid
- or if the value at this index is <b>nil</b>,
- and 0 otherwise.
- <hr><h3><a name="lua_isnumber"><code>lua_isnumber</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isnumber (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a number
- or a string convertible to a number,
- and 0 otherwise.
- <hr><h3><a name="lua_isstring"><code>lua_isstring</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isstring (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a string
- or a number (which is always convertible to a string),
- and 0 otherwise.
- <hr><h3><a name="lua_istable"><code>lua_istable</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_istable (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a table,
- and 0 otherwise.
- <hr><h3><a name="lua_isthread"><code>lua_isthread</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isthread (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a thread,
- and 0 otherwise.
- <hr><h3><a name="lua_isuserdata"><code>lua_isuserdata</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isuserdata (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a userdata
- (either full or light), and 0 otherwise.
- <hr><h3><a name="lua_len"><code>lua_len</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>void lua_len (lua_State *L, int index);</pre>
- <p>
- Returns the "length" of the value at the given index;
- it is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.6">§3.4.6</a>).
- The result is pushed on the stack.
- <hr><h3><a name="lua_load"><code>lua_load</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>int lua_load (lua_State *L,
- lua_Reader reader,
- void *data,
- const char *source,
- const char *mode);</pre>
- <p>
- Loads a Lua chunk (without running it).
- If there are no errors,
- <code>lua_load</code> pushes the compiled chunk as a Lua
- function on top of the stack.
- Otherwise, it pushes an error message.
- <p>
- The return values of <code>lua_load</code> are:
- <ul>
- <li><b><a href="#pdf-LUA_OK"><code>LUA_OK</code></a>: </b> no errors;</li>
- <li><b><a name="pdf-LUA_ERRSYNTAX"><code>LUA_ERRSYNTAX</code></a>: </b>
- syntax error during precompilation;</li>
- <li><b><a href="#pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b>
- memory allocation error;</li>
- <li><b><a href="#pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b>
- error while running a <code>__gc</code> metamethod.
- (This error has no relation with the chunk being loaded.
- It is generated by the garbage collector.)
- </li>
- </ul>
- <p>
- The <code>lua_load</code> function uses a user-supplied <code>reader</code> function
- to read the chunk (see <a href="#lua_Reader"><code>lua_Reader</code></a>).
- The <code>data</code> argument is an opaque value passed to the reader function.
- <p>
- The <code>source</code> argument gives a name to the chunk,
- which is used for error messages and in debug information (see <a href="#4.9">§4.9</a>).
- <p>
- <code>lua_load</code> automatically detects whether the chunk is text or binary
- and loads it accordingly (see program <code>luac</code>).
- The string <code>mode</code> works as in function <a href="#pdf-load"><code>load</code></a>,
- with the addition that
- a <code>NULL</code> value is equivalent to the string "<code>bt</code>".
- <p>
- <code>lua_load</code> uses the stack internally,
- so the reader function should always leave the stack
- unmodified when returning.
- <p>
- If the resulting function has one upvalue,
- this upvalue is set to the value of the global environment
- stored at index <code>LUA_RIDX_GLOBALS</code> in the registry (see <a href="#4.5">§4.5</a>).
- When loading main chunks,
- this upvalue will be the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>).
- <hr><h3><a name="lua_newstate"><code>lua_newstate</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_State *lua_newstate (lua_Alloc f, void *ud);</pre>
- <p>
- Creates a new thread running in a new, independent state.
- Returns <code>NULL</code> if cannot create the thread or the state
- (due to lack of memory).
- The argument <code>f</code> is the allocator function;
- Lua does all memory allocation for this state through this function.
- The second argument, <code>ud</code>, is an opaque pointer that Lua
- passes to the allocator in every call.
- <hr><h3><a name="lua_newtable"><code>lua_newtable</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>void lua_newtable (lua_State *L);</pre>
- <p>
- Creates a new empty table and pushes it onto the stack.
- It is equivalent to <code>lua_createtable(L, 0, 0)</code>.
- <hr><h3><a name="lua_newthread"><code>lua_newthread</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>lua_State *lua_newthread (lua_State *L);</pre>
- <p>
- Creates a new thread, pushes it on the stack,
- and returns a pointer to a <a href="#lua_State"><code>lua_State</code></a> that represents this new thread.
- The new thread returned by this function shares with the original thread
- its global environment,
- but has an independent execution stack.
- <p>
- There is no explicit function to close or to destroy a thread.
- Threads are subject to garbage collection,
- like any Lua object.
- <hr><h3><a name="lua_newuserdata"><code>lua_newuserdata</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>void *lua_newuserdata (lua_State *L, size_t size);</pre>
- <p>
- This function allocates a new block of memory with the given size,
- pushes onto the stack a new full userdata with the block address,
- and returns this address.
- The host program can freely use this memory.
- <hr><h3><a name="lua_next"><code>lua_next</code></a></h3><p>
- <span class="apii">[-1, +(2|0), <em>e</em>]</span>
- <pre>int lua_next (lua_State *L, int index);</pre>
- <p>
- Pops a key from the stack,
- and pushes a key–value pair from the table at the given index
- (the "next" pair after the given key).
- If there are no more elements in the table,
- then <a href="#lua_next"><code>lua_next</code></a> returns 0 (and pushes nothing).
- <p>
- A typical traversal looks like this:
- <pre>
- /* table is in the stack at index 't' */
- lua_pushnil(L); /* first key */
- while (lua_next(L, t) != 0) {
- /* uses 'key' (at index -2) and 'value' (at index -1) */
- printf("%s - %s\n",
- lua_typename(L, lua_type(L, -2)),
- lua_typename(L, lua_type(L, -1)));
- /* removes 'value'; keeps 'key' for next iteration */
- lua_pop(L, 1);
- }
- </pre>
- <p>
- While traversing a table,
- do not call <a href="#lua_tolstring"><code>lua_tolstring</code></a> directly on a key,
- unless you know that the key is actually a string.
- Recall that <a href="#lua_tolstring"><code>lua_tolstring</code></a> may change
- the value at the given index;
- this confuses the next call to <a href="#lua_next"><code>lua_next</code></a>.
- <p>
- See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying
- the table during its traversal.
- <hr><h3><a name="lua_Number"><code>lua_Number</code></a></h3>
- <pre>typedef double lua_Number;</pre>
- <p>
- The type of numbers in Lua.
- By default, it is double, but that can be changed in <code>luaconf.h</code>.
- Through this configuration file you can change
- Lua to operate with another type for numbers (e.g., float or long).
- <hr><h3><a name="lua_pcall"><code>lua_pcall</code></a></h3><p>
- <span class="apii">[-(nargs + 1), +(nresults|1), –]</span>
- <pre>int lua_pcall (lua_State *L, int nargs, int nresults, int msgh);</pre>
- <p>
- Calls a function in protected mode.
- <p>
- Both <code>nargs</code> and <code>nresults</code> have the same meaning as
- in <a href="#lua_call"><code>lua_call</code></a>.
- If there are no errors during the call,
- <a href="#lua_pcall"><code>lua_pcall</code></a> behaves exactly like <a href="#lua_call"><code>lua_call</code></a>.
- However, if there is any error,
- <a href="#lua_pcall"><code>lua_pcall</code></a> catches it,
- pushes a single value on the stack (the error message),
- and returns an error code.
- Like <a href="#lua_call"><code>lua_call</code></a>,
- <a href="#lua_pcall"><code>lua_pcall</code></a> always removes the function
- and its arguments from the stack.
- <p>
- If <code>msgh</code> is 0,
- then the error message returned on the stack
- is exactly the original error message.
- Otherwise, <code>msgh</code> is the stack index of a
- <em>message handler</em>.
- (In the current implementation, this index cannot be a pseudo-index.)
- In case of runtime errors,
- this function will be called with the error message
- and its return value will be the message
- returned on the stack by <a href="#lua_pcall"><code>lua_pcall</code></a>.
- <p>
- Typically, the message handler is used to add more debug
- information to the error message, such as a stack traceback.
- Such information cannot be gathered after the return of <a href="#lua_pcall"><code>lua_pcall</code></a>,
- since by then the stack has unwound.
- <p>
- The <a href="#lua_pcall"><code>lua_pcall</code></a> function returns one of the following codes
- (defined in <code>lua.h</code>):
- <ul>
- <li><b><a name="pdf-LUA_OK"><code>LUA_OK</code></a> (0): </b>
- success.</li>
- <li><b><a name="pdf-LUA_ERRRUN"><code>LUA_ERRRUN</code></a>: </b>
- a runtime error.
- </li>
- <li><b><a name="pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b>
- memory allocation error.
- For such errors, Lua does not call the message handler.
- </li>
- <li><b><a name="pdf-LUA_ERRERR"><code>LUA_ERRERR</code></a>: </b>
- error while running the message handler.
- </li>
- <li><b><a name="pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b>
- error while running a <code>__gc</code> metamethod.
- (This error typically has no relation with the function being called.
- It is generated by the garbage collector.)
- </li>
- </ul>
- <hr><h3><a name="lua_pcallk"><code>lua_pcallk</code></a></h3><p>
- <span class="apii">[-(nargs + 1), +(nresults|1), –]</span>
- <pre>int lua_pcallk (lua_State *L,
- int nargs,
- int nresults,
- int errfunc,
- int ctx,
- lua_CFunction k);</pre>
- <p>
- This function behaves exactly like <a href="#lua_pcall"><code>lua_pcall</code></a>,
- but allows the called function to yield (see <a href="#4.7">§4.7</a>).
- <hr><h3><a name="lua_pop"><code>lua_pop</code></a></h3><p>
- <span class="apii">[-n, +0, –]</span>
- <pre>void lua_pop (lua_State *L, int n);</pre>
- <p>
- Pops <code>n</code> elements from the stack.
- <hr><h3><a name="lua_pushboolean"><code>lua_pushboolean</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushboolean (lua_State *L, int b);</pre>
- <p>
- Pushes a boolean value with value <code>b</code> onto the stack.
- <hr><h3><a name="lua_pushcclosure"><code>lua_pushcclosure</code></a></h3><p>
- <span class="apii">[-n, +1, <em>e</em>]</span>
- <pre>void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);</pre>
- <p>
- Pushes a new C closure onto the stack.
- <p>
- When a C function is created,
- it is possible to associate some values with it,
- thus creating a C closure (see <a href="#4.4">§4.4</a>);
- these values are then accessible to the function whenever it is called.
- To associate values with a C function,
- first these values should be pushed onto the stack
- (when there are multiple values, the first value is pushed first).
- Then <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>
- is called to create and push the C function onto the stack,
- with the argument <code>n</code> telling how many values should be
- associated with the function.
- <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> also pops these values from the stack.
- <p>
- The maximum value for <code>n</code> is 255.
- <p>
- When <code>n</code> is zero,
- this function creates a <em>light C function</em>,
- which is just a pointer to the C function.
- In that case, it never throws a memory error.
- <hr><h3><a name="lua_pushcfunction"><code>lua_pushcfunction</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushcfunction (lua_State *L, lua_CFunction f);</pre>
- <p>
- Pushes a C function onto the stack.
- This function receives a pointer to a C function
- and pushes onto the stack a Lua value of type <code>function</code> that,
- when called, invokes the corresponding C function.
- <p>
- Any function to be registered in Lua must
- follow the correct protocol to receive its parameters
- and return its results (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
- <p>
- <code>lua_pushcfunction</code> is defined as a macro:
- <pre>
- #define lua_pushcfunction(L,f) lua_pushcclosure(L,f,0)
- </pre><p>
- Note that <code>f</code> is used twice.
- <hr><h3><a name="lua_pushfstring"><code>lua_pushfstring</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>const char *lua_pushfstring (lua_State *L, const char *fmt, ...);</pre>
- <p>
- Pushes onto the stack a formatted string
- and returns a pointer to this string.
- It is similar to the ISO C function <code>sprintf</code>,
- but has some important differences:
- <ul>
- <li>
- You do not have to allocate space for the result:
- the result is a Lua string and Lua takes care of memory allocation
- (and deallocation, through garbage collection).
- </li>
- <li>
- The conversion specifiers are quite restricted.
- There are no flags, widths, or precisions.
- The conversion specifiers can only be
- '<code>%%</code>' (inserts a '<code>%</code>' in the string),
- '<code>%s</code>' (inserts a zero-terminated string, with no size restrictions),
- '<code>%f</code>' (inserts a <a href="#lua_Number"><code>lua_Number</code></a>),
- '<code>%p</code>' (inserts a pointer as a hexadecimal numeral),
- '<code>%d</code>' (inserts an <code>int</code>), and
- '<code>%c</code>' (inserts an <code>int</code> as a byte).
- </li>
- </ul>
- <hr><h3><a name="lua_pushglobaltable"><code>lua_pushglobaltable</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushglobaltable (lua_State *L);</pre>
- <p>
- Pushes the global environment onto the stack.
- <hr><h3><a name="lua_pushinteger"><code>lua_pushinteger</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushinteger (lua_State *L, lua_Integer n);</pre>
- <p>
- Pushes a number with value <code>n</code> onto the stack.
- <hr><h3><a name="lua_pushlightuserdata"><code>lua_pushlightuserdata</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushlightuserdata (lua_State *L, void *p);</pre>
- <p>
- Pushes a light userdata onto the stack.
- <p>
- Userdata represent C values in Lua.
- A <em>light userdata</em> represents a pointer, a <code>void*</code>.
- It is a value (like a number):
- you do not create it, it has no individual metatable,
- and it is not collected (as it was never created).
- A light userdata is equal to "any"
- light userdata with the same C address.
- <hr><h3><a name="lua_pushliteral"><code>lua_pushliteral</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>const char *lua_pushliteral (lua_State *L, const char *s);</pre>
- <p>
- This macro is equivalent to <a href="#lua_pushlstring"><code>lua_pushlstring</code></a>,
- but can be used only when <code>s</code> is a literal string.
- It automatically provides the string length.
- <hr><h3><a name="lua_pushlstring"><code>lua_pushlstring</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>const char *lua_pushlstring (lua_State *L, const char *s, size_t len);</pre>
- <p>
- Pushes the string pointed to by <code>s</code> with size <code>len</code>
- onto the stack.
- Lua makes (or reuses) an internal copy of the given string,
- so the memory at <code>s</code> can be freed or reused immediately after
- the function returns.
- The string can contain any binary data,
- including embedded zeros.
- <p>
- Returns a pointer to the internal copy of the string.
- <hr><h3><a name="lua_pushnil"><code>lua_pushnil</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushnil (lua_State *L);</pre>
- <p>
- Pushes a nil value onto the stack.
- <hr><h3><a name="lua_pushnumber"><code>lua_pushnumber</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushnumber (lua_State *L, lua_Number n);</pre>
- <p>
- Pushes a number with value <code>n</code> onto the stack.
- <hr><h3><a name="lua_pushstring"><code>lua_pushstring</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>const char *lua_pushstring (lua_State *L, const char *s);</pre>
- <p>
- Pushes the zero-terminated string pointed to by <code>s</code>
- onto the stack.
- Lua makes (or reuses) an internal copy of the given string,
- so the memory at <code>s</code> can be freed or reused immediately after
- the function returns.
- <p>
- Returns a pointer to the internal copy of the string.
- <p>
- If <code>s</code> is <code>NULL</code>, pushes <b>nil</b> and returns <code>NULL</code>.
- <hr><h3><a name="lua_pushthread"><code>lua_pushthread</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>int lua_pushthread (lua_State *L);</pre>
- <p>
- Pushes the thread represented by <code>L</code> onto the stack.
- Returns 1 if this thread is the main thread of its state.
- <hr><h3><a name="lua_pushunsigned"><code>lua_pushunsigned</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushunsigned (lua_State *L, lua_Unsigned n);</pre>
- <p>
- Pushes a number with value <code>n</code> onto the stack.
- <hr><h3><a name="lua_pushvalue"><code>lua_pushvalue</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushvalue (lua_State *L, int index);</pre>
- <p>
- Pushes a copy of the element at the given index
- onto the stack.
- <hr><h3><a name="lua_pushvfstring"><code>lua_pushvfstring</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>const char *lua_pushvfstring (lua_State *L,
- const char *fmt,
- va_list argp);</pre>
- <p>
- Equivalent to <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>, except that it receives a <code>va_list</code>
- instead of a variable number of arguments.
- <hr><h3><a name="lua_rawequal"><code>lua_rawequal</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_rawequal (lua_State *L, int index1, int index2);</pre>
- <p>
- Returns 1 if the two values in indices <code>index1</code> and
- <code>index2</code> are primitively equal
- (that is, without calling metamethods).
- Otherwise returns 0.
- Also returns 0 if any of the indices are non valid.
- <hr><h3><a name="lua_rawget"><code>lua_rawget</code></a></h3><p>
- <span class="apii">[-1, +1, –]</span>
- <pre>void lua_rawget (lua_State *L, int index);</pre>
- <p>
- Similar to <a href="#lua_gettable"><code>lua_gettable</code></a>, but does a raw access
- (i.e., without metamethods).
- <hr><h3><a name="lua_rawgeti"><code>lua_rawgeti</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_rawgeti (lua_State *L, int index, int n);</pre>
- <p>
- Pushes onto the stack the value <code>t[n]</code>,
- where <code>t</code> is the table at the given index.
- The access is raw;
- that is, it does not invoke metamethods.
- <hr><h3><a name="lua_rawgetp"><code>lua_rawgetp</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_rawgetp (lua_State *L, int index, const void *p);</pre>
- <p>
- Pushes onto the stack the value <code>t[k]</code>,
- where <code>t</code> is the table at the given index and
- <code>k</code> is the pointer <code>p</code> represented as a light userdata.
- The access is raw;
- that is, it does not invoke metamethods.
- <hr><h3><a name="lua_rawlen"><code>lua_rawlen</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>size_t lua_rawlen (lua_State *L, int index);</pre>
- <p>
- Returns the raw "length" of the value at the given index:
- for strings, this is the string length;
- for tables, this is the result of the length operator ('<code>#</code>')
- with no metamethods;
- for userdata, this is the size of the block of memory allocated
- for the userdata;
- for other values, it is 0.
- <hr><h3><a name="lua_rawset"><code>lua_rawset</code></a></h3><p>
- <span class="apii">[-2, +0, <em>e</em>]</span>
- <pre>void lua_rawset (lua_State *L, int index);</pre>
- <p>
- Similar to <a href="#lua_settable"><code>lua_settable</code></a>, but does a raw assignment
- (i.e., without metamethods).
- <hr><h3><a name="lua_rawseti"><code>lua_rawseti</code></a></h3><p>
- <span class="apii">[-1, +0, <em>e</em>]</span>
- <pre>void lua_rawseti (lua_State *L, int index, int n);</pre>
- <p>
- Does the equivalent of <code>t[n] = v</code>,
- where <code>t</code> is the table at the given index
- and <code>v</code> is the value at the top of the stack.
- <p>
- This function pops the value from the stack.
- The assignment is raw;
- that is, it does not invoke metamethods.
- <hr><h3><a name="lua_rawsetp"><code>lua_rawsetp</code></a></h3><p>
- <span class="apii">[-1, +0, <em>e</em>]</span>
- <pre>void lua_rawsetp (lua_State *L, int index, const void *p);</pre>
- <p>
- Does the equivalent of <code>t[k] = v</code>,
- where <code>t</code> is the table at the given index,
- <code>k</code> is the pointer <code>p</code> represented as a light userdata,
- and <code>v</code> is the value at the top of the stack.
- <p>
- This function pops the value from the stack.
- The assignment is raw;
- that is, it does not invoke metamethods.
- <hr><h3><a name="lua_Reader"><code>lua_Reader</code></a></h3>
- <pre>typedef const char * (*lua_Reader) (lua_State *L,
- void *data,
- size_t *size);</pre>
- <p>
- The reader function used by <a href="#lua_load"><code>lua_load</code></a>.
- Every time it needs another piece of the chunk,
- <a href="#lua_load"><code>lua_load</code></a> calls the reader,
- passing along its <code>data</code> parameter.
- The reader must return a pointer to a block of memory
- with a new piece of the chunk
- and set <code>size</code> to the block size.
- The block must exist until the reader function is called again.
- To signal the end of the chunk,
- the reader must return <code>NULL</code> or set <code>size</code> to zero.
- The reader function may return pieces of any size greater than zero.
- <hr><h3><a name="lua_register"><code>lua_register</code></a></h3><p>
- <span class="apii">[-0, +0, <em>e</em>]</span>
- <pre>void lua_register (lua_State *L, const char *name, lua_CFunction f);</pre>
- <p>
- Sets the C function <code>f</code> as the new value of global <code>name</code>.
- It is defined as a macro:
- <pre>
- #define lua_register(L,n,f) \
- (lua_pushcfunction(L, f), lua_setglobal(L, n))
- </pre>
- <hr><h3><a name="lua_remove"><code>lua_remove</code></a></h3><p>
- <span class="apii">[-1, +0, –]</span>
- <pre>void lua_remove (lua_State *L, int index);</pre>
- <p>
- Removes the element at the given valid index,
- shifting down the elements above this index to fill the gap.
- This function cannot be called with a pseudo-index,
- because a pseudo-index is not an actual stack position.
- <hr><h3><a name="lua_replace"><code>lua_replace</code></a></h3><p>
- <span class="apii">[-1, +0, –]</span>
- <pre>void lua_replace (lua_State *L, int index);</pre>
- <p>
- Moves the top element into the given valid index
- without shifting any element
- (therefore replacing the value at the given index),
- and then pops the top element.
- <hr><h3><a name="lua_resume"><code>lua_resume</code></a></h3><p>
- <span class="apii">[-?, +?, –]</span>
- <pre>int lua_resume (lua_State *L, lua_State *from, int nargs);</pre>
- <p>
- Starts and resumes a coroutine in a given thread.
- <p>
- To start a coroutine,
- you push onto the thread stack the main function plus any arguments;
- then you call <a href="#lua_resume"><code>lua_resume</code></a>,
- with <code>nargs</code> being the number of arguments.
- This call returns when the coroutine suspends or finishes its execution.
- When it returns, the stack contains all values passed to <a href="#lua_yield"><code>lua_yield</code></a>,
- or all values returned by the body function.
- <a href="#lua_resume"><code>lua_resume</code></a> returns
- <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the coroutine yields,
- <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> if the coroutine finishes its execution
- without errors,
- or an error code in case of errors (see <a href="#lua_pcall"><code>lua_pcall</code></a>).
- <p>
- In case of errors,
- the stack is not unwound,
- so you can use the debug API over it.
- The error message is on the top of the stack.
- <p>
- To resume a coroutine,
- you remove any results from the last <a href="#lua_yield"><code>lua_yield</code></a>,
- put on its stack only the values to
- be passed as results from <code>yield</code>,
- and then call <a href="#lua_resume"><code>lua_resume</code></a>.
- <p>
- The parameter <code>from</code> represents the coroutine that is resuming <code>L</code>.
- If there is no such coroutine,
- this parameter can be <code>NULL</code>.
- <hr><h3><a name="lua_setallocf"><code>lua_setallocf</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);</pre>
- <p>
- Changes the allocator function of a given state to <code>f</code>
- with user data <code>ud</code>.
- <hr><h3><a name="lua_setfield"><code>lua_setfield</code></a></h3><p>
- <span class="apii">[-1, +0, <em>e</em>]</span>
- <pre>void lua_setfield (lua_State *L, int index, const char *k);</pre>
- <p>
- Does the equivalent to <code>t[k] = v</code>,
- where <code>t</code> is the value at the given index
- and <code>v</code> is the value at the top of the stack.
- <p>
- This function pops the value from the stack.
- As in Lua, this function may trigger a metamethod
- for the "newindex" event (see <a href="#2.4">§2.4</a>).
- <hr><h3><a name="lua_setglobal"><code>lua_setglobal</code></a></h3><p>
- <span class="apii">[-1, +0, <em>e</em>]</span>
- <pre>void lua_setglobal (lua_State *L, const char *name);</pre>
- <p>
- Pops a value from the stack and
- sets it as the new value of global <code>name</code>.
- <hr><h3><a name="lua_setmetatable"><code>lua_setmetatable</code></a></h3><p>
- <span class="apii">[-1, +0, –]</span>
- <pre>void lua_setmetatable (lua_State *L, int index);</pre>
- <p>
- Pops a table from the stack and
- sets it as the new metatable for the value at the given index.
- <hr><h3><a name="lua_settable"><code>lua_settable</code></a></h3><p>
- <span class="apii">[-2, +0, <em>e</em>]</span>
- <pre>void lua_settable (lua_State *L, int index);</pre>
- <p>
- Does the equivalent to <code>t[k] = v</code>,
- where <code>t</code> is the value at the given index,
- <code>v</code> is the value at the top of the stack,
- and <code>k</code> is the value just below the top.
- <p>
- This function pops both the key and the value from the stack.
- As in Lua, this function may trigger a metamethod
- for the "newindex" event (see <a href="#2.4">§2.4</a>).
- <hr><h3><a name="lua_settop"><code>lua_settop</code></a></h3><p>
- <span class="apii">[-?, +?, –]</span>
- <pre>void lua_settop (lua_State *L, int index);</pre>
- <p>
- Accepts any index, or 0,
- and sets the stack top to this index.
- If the new top is larger than the old one,
- then the new elements are filled with <b>nil</b>.
- If <code>index</code> is 0, then all stack elements are removed.
- <hr><h3><a name="lua_setuservalue"><code>lua_setuservalue</code></a></h3><p>
- <span class="apii">[-1, +0, –]</span>
- <pre>void lua_setuservalue (lua_State *L, int index);</pre>
- <p>
- Pops a table or <b>nil</b> from the stack and sets it as
- the new value associated to the userdata at the given index.
- <hr><h3><a name="lua_State"><code>lua_State</code></a></h3>
- <pre>typedef struct lua_State lua_State;</pre>
- <p>
- An opaque structure that points to a thread and indirectly
- (through the thread) to the whole state of a Lua interpreter.
- The Lua library is fully reentrant:
- it has no global variables.
- All information about a state is accessible through this structure.
- <p>
- A pointer to this structure must be passed as the first argument to
- every function in the library, except to <a href="#lua_newstate"><code>lua_newstate</code></a>,
- which creates a Lua state from scratch.
- <hr><h3><a name="lua_status"><code>lua_status</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_status (lua_State *L);</pre>
- <p>
- Returns the status of the thread <code>L</code>.
- <p>
- The status can be 0 (<a href="#pdf-LUA_OK"><code>LUA_OK</code></a>) for a normal thread,
- an error code if the thread finished the execution
- of a <a href="#lua_resume"><code>lua_resume</code></a> with an error,
- or <a name="pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the thread is suspended.
- <p>
- You can only call functions in threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>.
- You can resume threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>
- (to start a new coroutine) or <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a>
- (to resume a coroutine).
- <hr><h3><a name="lua_toboolean"><code>lua_toboolean</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_toboolean (lua_State *L, int index);</pre>
- <p>
- Converts the Lua value at the given index to a C boolean
- value (0 or 1).
- Like all tests in Lua,
- <a href="#lua_toboolean"><code>lua_toboolean</code></a> returns true for any Lua value
- different from <b>false</b> and <b>nil</b>;
- otherwise it returns false.
- (If you want to accept only actual boolean values,
- use <a href="#lua_isboolean"><code>lua_isboolean</code></a> to test the value's type.)
- <hr><h3><a name="lua_tocfunction"><code>lua_tocfunction</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_CFunction lua_tocfunction (lua_State *L, int index);</pre>
- <p>
- Converts a value at the given index to a C function.
- That value must be a C function;
- otherwise, returns <code>NULL</code>.
- <hr><h3><a name="lua_tointeger"><code>lua_tointeger</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Integer lua_tointeger (lua_State *L, int index);</pre>
- <p>
- Equivalent to <a href="#lua_tointegerx"><code>lua_tointegerx</code></a> with <code>isnum</code> equal to <code>NULL</code>.
- <hr><h3><a name="lua_tointegerx"><code>lua_tointegerx</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Integer lua_tointegerx (lua_State *L, int index, int *isnum);</pre>
- <p>
- Converts the Lua value at the given index
- to the signed integral type <a href="#lua_Integer"><code>lua_Integer</code></a>.
- The Lua value must be a number or a string convertible to a number
- (see <a href="#3.4.2">§3.4.2</a>);
- otherwise, <code>lua_tointegerx</code> returns 0.
- <p>
- If the number is not an integer,
- it is truncated in some non-specified way.
- <p>
- If <code>isnum</code> is not <code>NULL</code>,
- its referent is assigned a boolean value that
- indicates whether the operation succeeded.
- <hr><h3><a name="lua_tolstring"><code>lua_tolstring</code></a></h3><p>
- <span class="apii">[-0, +0, <em>e</em>]</span>
- <pre>const char *lua_tolstring (lua_State *L, int index, size_t *len);</pre>
- <p>
- Converts the Lua value at the given index to a C string.
- If <code>len</code> is not <code>NULL</code>,
- it also sets <code>*len</code> with the string length.
- The Lua value must be a string or a number;
- otherwise, the function returns <code>NULL</code>.
- If the value is a number,
- then <code>lua_tolstring</code> also
- <em>changes the actual value in the stack to a string</em>.
- (This change confuses <a href="#lua_next"><code>lua_next</code></a>
- when <code>lua_tolstring</code> is applied to keys during a table traversal.)
- <p>
- <code>lua_tolstring</code> returns a fully aligned pointer
- to a string inside the Lua state.
- This string always has a zero ('<code>\0</code>')
- after its last character (as in C),
- but can contain other zeros in its body.
- Because Lua has garbage collection,
- there is no guarantee that the pointer returned by <code>lua_tolstring</code>
- will be valid after the corresponding value is removed from the stack.
- <hr><h3><a name="lua_tonumber"><code>lua_tonumber</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Number lua_tonumber (lua_State *L, int index);</pre>
- <p>
- Equivalent to <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> with <code>isnum</code> equal to <code>NULL</code>.
- <hr><h3><a name="lua_tonumberx"><code>lua_tonumberx</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Number lua_tonumberx (lua_State *L, int index, int *isnum);</pre>
- <p>
- Converts the Lua value at the given index
- to the C type <a href="#lua_Number"><code>lua_Number</code></a> (see <a href="#lua_Number"><code>lua_Number</code></a>).
- The Lua value must be a number or a string convertible to a number
- (see <a href="#3.4.2">§3.4.2</a>);
- otherwise, <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> returns 0.
- <p>
- If <code>isnum</code> is not <code>NULL</code>,
- its referent is assigned a boolean value that
- indicates whether the operation succeeded.
- <hr><h3><a name="lua_topointer"><code>lua_topointer</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>const void *lua_topointer (lua_State *L, int index);</pre>
- <p>
- Converts the value at the given index to a generic
- C pointer (<code>void*</code>).
- The value can be a userdata, a table, a thread, or a function;
- otherwise, <code>lua_topointer</code> returns <code>NULL</code>.
- Different objects will give different pointers.
- There is no way to convert the pointer back to its original value.
- <p>
- Typically this function is used only for debug information.
- <hr><h3><a name="lua_tostring"><code>lua_tostring</code></a></h3><p>
- <span class="apii">[-0, +0, <em>e</em>]</span>
- <pre>const char *lua_tostring (lua_State *L, int index);</pre>
- <p>
- Equivalent to <a href="#lua_tolstring"><code>lua_tolstring</code></a> with <code>len</code> equal to <code>NULL</code>.
- <hr><h3><a name="lua_tothread"><code>lua_tothread</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_State *lua_tothread (lua_State *L, int index);</pre>
- <p>
- Converts the value at the given index to a Lua thread
- (represented as <code>lua_State*</code>).
- This value must be a thread;
- otherwise, the function returns <code>NULL</code>.
- <hr><h3><a name="lua_tounsigned"><code>lua_tounsigned</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Unsigned lua_tounsigned (lua_State *L, int index);</pre>
- <p>
- Equivalent to <a href="#lua_tounsignedx"><code>lua_tounsignedx</code></a> with <code>isnum</code> equal to <code>NULL</code>.
- <hr><h3><a name="lua_tounsignedx"><code>lua_tounsignedx</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Unsigned lua_tounsignedx (lua_State *L, int index, int *isnum);</pre>
- <p>
- Converts the Lua value at the given index
- to the unsigned integral type <a href="#lua_Unsigned"><code>lua_Unsigned</code></a>.
- The Lua value must be a number or a string convertible to a number
- (see <a href="#3.4.2">§3.4.2</a>);
- otherwise, <code>lua_tounsignedx</code> returns 0.
- <p>
- If the number is not an integer,
- it is truncated in some non-specified way.
- If the number is outside the range of representable values,
- it is normalized to the remainder of its division by
- one more than the maximum representable value.
- <p>
- If <code>isnum</code> is not <code>NULL</code>,
- its referent is assigned a boolean value that
- indicates whether the operation succeeded.
- <hr><h3><a name="lua_touserdata"><code>lua_touserdata</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void *lua_touserdata (lua_State *L, int index);</pre>
- <p>
- If the value at the given index is a full userdata,
- returns its block address.
- If the value is a light userdata,
- returns its pointer.
- Otherwise, returns <code>NULL</code>.
- <hr><h3><a name="lua_type"><code>lua_type</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_type (lua_State *L, int index);</pre>
- <p>
- Returns the type of the value in the given valid index,
- or <code>LUA_TNONE</code> for a non-valid (but acceptable) index.
- The types returned by <a href="#lua_type"><code>lua_type</code></a> are coded by the following constants
- defined in <code>lua.h</code>:
- <a name="pdf-LUA_TNIL"><code>LUA_TNIL</code></a>,
- <a name="pdf-LUA_TNUMBER"><code>LUA_TNUMBER</code></a>,
- <a name="pdf-LUA_TBOOLEAN"><code>LUA_TBOOLEAN</code></a>,
- <a name="pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>,
- <a name="pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>,
- <a name="pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>,
- <a name="pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>,
- <a name="pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a>,
- and
- <a name="pdf-LUA_TLIGHTUSERDATA"><code>LUA_TLIGHTUSERDATA</code></a>.
- <hr><h3><a name="lua_typename"><code>lua_typename</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>const char *lua_typename (lua_State *L, int tp);</pre>
- <p>
- Returns the name of the type encoded by the value <code>tp</code>,
- which must be one the values returned by <a href="#lua_type"><code>lua_type</code></a>.
- <hr><h3><a name="lua_Unsigned"><code>lua_Unsigned</code></a></h3>
- <pre>typedef unsigned long lua_Unsigned;</pre>
- <p>
- The type used by the Lua API to represent unsigned integral values.
- It must have at least 32 bits.
- <p>
- By default it is an <code>unsigned int</code> or an <code>unsigned long</code>,
- whichever can hold 32-bit values.
- <hr><h3><a name="lua_upvalueindex"><code>lua_upvalueindex</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_upvalueindex (int i);</pre>
- <p>
- Returns the pseudo-index that represents the <code>i</code>-th upvalue of
- the running function (see <a href="#4.4">§4.4</a>).
- <hr><h3><a name="lua_version"><code>lua_version</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>const lua_Number *lua_version (lua_State *L);</pre>
- <p>
- Returns the address of the version number stored in the Lua core.
- When called with a valid <a href="#lua_State"><code>lua_State</code></a>,
- returns the address of the version used to create that state.
- When called with <code>NULL</code>,
- returns the address of the version running the call.
- <hr><h3><a name="lua_Writer"><code>lua_Writer</code></a></h3>
- <pre>typedef int (*lua_Writer) (lua_State *L,
- const void* p,
- size_t sz,
- void* ud);</pre>
- <p>
- The type of the writer function used by <a href="#lua_dump"><code>lua_dump</code></a>.
- Every time it produces another piece of chunk,
- <a href="#lua_dump"><code>lua_dump</code></a> calls the writer,
- passing along the buffer to be written (<code>p</code>),
- its size (<code>sz</code>),
- and the <code>data</code> parameter supplied to <a href="#lua_dump"><code>lua_dump</code></a>.
- <p>
- The writer returns an error code:
- 0 means no errors;
- any other value means an error and stops <a href="#lua_dump"><code>lua_dump</code></a> from
- calling the writer again.
- <hr><h3><a name="lua_xmove"><code>lua_xmove</code></a></h3><p>
- <span class="apii">[-?, +?, –]</span>
- <pre>void lua_xmove (lua_State *from, lua_State *to, int n);</pre>
- <p>
- Exchange values between different threads of the same state.
- <p>
- This function pops <code>n</code> values from the stack <code>from</code>,
- and pushes them onto the stack <code>to</code>.
- <hr><h3><a name="lua_yield"><code>lua_yield</code></a></h3><p>
- <span class="apii">[-?, +?, –]</span>
- <pre>int lua_yield (lua_State *L, int nresults);</pre>
- <p>
- This function is equivalent to <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
- but it has no continuation (see <a href="#4.7">§4.7</a>).
- Therefore, when the thread resumes,
- it returns to the function that called
- the function calling <code>lua_yield</code>.
- <hr><h3><a name="lua_yieldk"><code>lua_yieldk</code></a></h3><p>
- <span class="apii">[-?, +?, –]</span>
- <pre>int lua_yieldk (lua_State *L, int nresults, int ctx, lua_CFunction k);</pre>
- <p>
- Yields a coroutine.
- <p>
- This function should only be called as the
- return expression of a C function, as follows:
- <pre>
- return lua_yieldk (L, n, i, k);
- </pre><p>
- When a C function calls <a href="#lua_yieldk"><code>lua_yieldk</code></a> in that way,
- the running coroutine suspends its execution,
- and the call to <a href="#lua_resume"><code>lua_resume</code></a> that started this coroutine returns.
- The parameter <code>nresults</code> is the number of values from the stack
- that are passed as results to <a href="#lua_resume"><code>lua_resume</code></a>.
- <p>
- When the coroutine is resumed again,
- Lua calls the given continuation function <code>k</code> to continue
- the execution of the C function that yielded (see <a href="#4.7">§4.7</a>).
- This continuation function receives the same stack
- from the previous function,
- with the results removed and
- replaced by the arguments passed to <a href="#lua_resume"><code>lua_resume</code></a>.
- Moreover,
- the continuation function may access the value <code>ctx</code>
- by calling <a href="#lua_getctx"><code>lua_getctx</code></a>.
- <h2>4.9 – <a name="4.9">The Debug Interface</a></h2>
- <p>
- Lua has no built-in debugging facilities.
- Instead, it offers a special interface
- by means of functions and <em>hooks</em>.
- This interface allows the construction of different
- kinds of debuggers, profilers, and other tools
- that need "inside information" from the interpreter.
- <hr><h3><a name="lua_Debug"><code>lua_Debug</code></a></h3>
- <pre>typedef struct lua_Debug {
- int event;
- const char *name; /* (n) */
- const char *namewhat; /* (n) */
- const char *what; /* (S) */
- const char *source; /* (S) */
- int currentline; /* (l) */
- int linedefined; /* (S) */
- int lastlinedefined; /* (S) */
- unsigned char nups; /* (u) number of upvalues */
- unsigned char nparams; /* (u) number of parameters */
- char isvararg; /* (u) */
- char istailcall; /* (t) */
- char short_src[LUA_IDSIZE]; /* (S) */
- /* private part */
- <em>other fields</em>
- } lua_Debug;</pre>
- <p>
- A structure used to carry different pieces of
- information about a function or an activation record.
- <a href="#lua_getstack"><code>lua_getstack</code></a> fills only the private part
- of this structure, for later use.
- To fill the other fields of <a href="#lua_Debug"><code>lua_Debug</code></a> with useful information,
- call <a href="#lua_getinfo"><code>lua_getinfo</code></a>.
- <p>
- The fields of <a href="#lua_Debug"><code>lua_Debug</code></a> have the following meaning:
- <ul>
- <li><b><code>source</code>: </b>
- the source of the chunk that created the function.
- If <code>source</code> starts with a '<code>@</code>',
- it means that the function was defined in a file where
- the file name follows the '<code>@</code>'.
- If <code>source</code> starts with a '<code>=</code>',
- the remainder of its contents describe the source in a user-dependent manner.
- Otherwise,
- the function was defined in a string where
- <code>source</code> is that string.
- </li>
- <li><b><code>short_src</code>: </b>
- a "printable" version of <code>source</code>, to be used in error messages.
- </li>
- <li><b><code>linedefined</code>: </b>
- the line number where the definition of the function starts.
- </li>
- <li><b><code>lastlinedefined</code>: </b>
- the line number where the definition of the function ends.
- </li>
- <li><b><code>what</code>: </b>
- the string <code>"Lua"</code> if the function is a Lua function,
- <code>"C"</code> if it is a C function,
- <code>"main"</code> if it is the main part of a chunk.
- </li>
- <li><b><code>currentline</code>: </b>
- the current line where the given function is executing.
- When no line information is available,
- <code>currentline</code> is set to -1.
- </li>
- <li><b><code>name</code>: </b>
- a reasonable name for the given function.
- Because functions in Lua are first-class values,
- they do not have a fixed name:
- some functions can be the value of multiple global variables,
- while others can be stored only in a table field.
- The <code>lua_getinfo</code> function checks how the function was
- called to find a suitable name.
- If it cannot find a name,
- then <code>name</code> is set to <code>NULL</code>.
- </li>
- <li><b><code>namewhat</code>: </b>
- explains the <code>name</code> field.
- The value of <code>namewhat</code> can be
- <code>"global"</code>, <code>"local"</code>, <code>"method"</code>,
- <code>"field"</code>, <code>"upvalue"</code>, or <code>""</code> (the empty string),
- according to how the function was called.
- (Lua uses the empty string when no other option seems to apply.)
- </li>
- <li><b><code>istailcall</code>: </b>
- true if this function invocation was called by a tail call.
- In this case, the caller of this level is not in the stack.
- </li>
- <li><b><code>nups</code>: </b>
- the number of upvalues of the function.
- </li>
- <li><b><code>nparams</code>: </b>
- the number of fixed parameters of the function
- (always 0 for C functions).
- </li>
- <li><b><code>isvararg</code>: </b>
- true if the function is a vararg function
- (always true for C functions).
- </li>
- </ul>
- <hr><h3><a name="lua_gethook"><code>lua_gethook</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Hook lua_gethook (lua_State *L);</pre>
- <p>
- Returns the current hook function.
- <hr><h3><a name="lua_gethookcount"><code>lua_gethookcount</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_gethookcount (lua_State *L);</pre>
- <p>
- Returns the current hook count.
- <hr><h3><a name="lua_gethookmask"><code>lua_gethookmask</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_gethookmask (lua_State *L);</pre>
- <p>
- Returns the current hook mask.
- <hr><h3><a name="lua_getinfo"><code>lua_getinfo</code></a></h3><p>
- <span class="apii">[-(0|1), +(0|1|2), <em>e</em>]</span>
- <pre>int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);</pre>
- <p>
- Gets information about a specific function or function invocation.
- <p>
- To get information about a function invocation,
- the parameter <code>ar</code> must be a valid activation record that was
- filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or
- given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>).
- <p>
- To get information about a function you push it onto the stack
- and start the <code>what</code> string with the character '<code>></code>'.
- (In that case,
- <code>lua_getinfo</code> pops the function from the top of the stack.)
- For instance, to know in which line a function <code>f</code> was defined,
- you can write the following code:
- <pre>
- lua_Debug ar;
- lua_getglobal(L, "f"); /* get global 'f' */
- lua_getinfo(L, ">S", &ar);
- printf("%d\n", ar.linedefined);
- </pre>
- <p>
- Each character in the string <code>what</code>
- selects some fields of the structure <code>ar</code> to be filled or
- a value to be pushed on the stack:
- <ul>
- <li><b>'<code>n</code>': </b> fills in the field <code>name</code> and <code>namewhat</code>;
- </li>
- <li><b>'<code>S</code>': </b>
- fills in the fields <code>source</code>, <code>short_src</code>,
- <code>linedefined</code>, <code>lastlinedefined</code>, and <code>what</code>;
- </li>
- <li><b>'<code>l</code>': </b> fills in the field <code>currentline</code>;
- </li>
- <li><b>'<code>t</code>': </b> fills in the field <code>istailcall</code>;
- </li>
- <li><b>'<code>u</code>': </b> fills in the fields
- <code>nups</code>, <code>nparams</code>, and <code>isvararg</code>;
- </li>
- <li><b>'<code>f</code>': </b>
- pushes onto the stack the function that is
- running at the given level;
- </li>
- <li><b>'<code>L</code>': </b>
- pushes onto the stack a table whose indices are the
- numbers of the lines that are valid on the function.
- (A <em>valid line</em> is a line with some associated code,
- that is, a line where you can put a break point.
- Non-valid lines include empty lines and comments.)
- </li>
- </ul>
- <p>
- This function returns 0 on error
- (for instance, an invalid option in <code>what</code>).
- <hr><h3><a name="lua_getlocal"><code>lua_getlocal</code></a></h3><p>
- <span class="apii">[-0, +(0|1), –]</span>
- <pre>const char *lua_getlocal (lua_State *L, lua_Debug *ar, int n);</pre>
- <p>
- Gets information about a local variable of
- a given activation record or a given function.
- <p>
- In the first case,
- the parameter <code>ar</code> must be a valid activation record that was
- filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or
- given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>).
- The index <code>n</code> selects which local variable to inspect;
- see <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for details about variable indices
- and names.
- <p>
- <a href="#lua_getlocal"><code>lua_getlocal</code></a> pushes the variable's value onto the stack
- and returns its name.
- <p>
- In the second case, <code>ar</code> should be <code>NULL</code> and the function
- to be inspected must be at the top of the stack.
- In this case, only parameters of Lua functions are visible
- (as there is no information about what variables are active)
- and no values are pushed onto the stack.
- <p>
- Returns <code>NULL</code> (and pushes nothing)
- when the index is greater than
- the number of active local variables.
- <hr><h3><a name="lua_getstack"><code>lua_getstack</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_getstack (lua_State *L, int level, lua_Debug *ar);</pre>
- <p>
- Gets information about the interpreter runtime stack.
- <p>
- This function fills parts of a <a href="#lua_Debug"><code>lua_Debug</code></a> structure with
- an identification of the <em>activation record</em>
- of the function executing at a given level.
- Level 0 is the current running function,
- whereas level <em>n+1</em> is the function that has called level <em>n</em>
- (except for tail calls, which do not count on the stack).
- When there are no errors, <a href="#lua_getstack"><code>lua_getstack</code></a> returns 1;
- when called with a level greater than the stack depth,
- it returns 0.
- <hr><h3><a name="lua_getupvalue"><code>lua_getupvalue</code></a></h3><p>
- <span class="apii">[-0, +(0|1), –]</span>
- <pre>const char *lua_getupvalue (lua_State *L, int funcindex, int n);</pre>
- <p>
- Gets information about a closure's upvalue.
- (For Lua functions,
- upvalues are the external local variables that the function uses,
- and that are consequently included in its closure.)
- <a href="#lua_getupvalue"><code>lua_getupvalue</code></a> gets the index <code>n</code> of an upvalue,
- pushes the upvalue's value onto the stack,
- and returns its name.
- <code>funcindex</code> points to the closure in the stack.
- (Upvalues have no particular order,
- as they are active through the whole function.
- So, they are numbered in an arbitrary order.)
- <p>
- Returns <code>NULL</code> (and pushes nothing)
- when the index is greater than the number of upvalues.
- For C functions, this function uses the empty string <code>""</code>
- as a name for all upvalues.
- <hr><h3><a name="lua_Hook"><code>lua_Hook</code></a></h3>
- <pre>typedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);</pre>
- <p>
- Type for debugging hook functions.
- <p>
- Whenever a hook is called, its <code>ar</code> argument has its field
- <code>event</code> set to the specific event that triggered the hook.
- Lua identifies these events with the following constants:
- <a name="pdf-LUA_HOOKCALL"><code>LUA_HOOKCALL</code></a>, <a name="pdf-LUA_HOOKRET"><code>LUA_HOOKRET</code></a>,
- <a name="pdf-LUA_HOOKTAILCALL"><code>LUA_HOOKTAILCALL</code></a>, <a name="pdf-LUA_HOOKLINE"><code>LUA_HOOKLINE</code></a>,
- and <a name="pdf-LUA_HOOKCOUNT"><code>LUA_HOOKCOUNT</code></a>.
- Moreover, for line events, the field <code>currentline</code> is also set.
- To get the value of any other field in <code>ar</code>,
- the hook must call <a href="#lua_getinfo"><code>lua_getinfo</code></a>.
- <p>
- For call events, <code>event</code> can be <code>LUA_HOOKCALL</code>,
- the normal value, or <code>LUA_HOOKTAILCALL</code>, for a tail call;
- in this case, there will be no corresponding return event.
- <p>
- While Lua is running a hook, it disables other calls to hooks.
- Therefore, if a hook calls back Lua to execute a function or a chunk,
- this execution occurs without any calls to hooks.
- <p>
- Hook functions cannot have continuations,
- that is, they cannot call <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
- <a href="#lua_pcallk"><code>lua_pcallk</code></a>, or <a href="#lua_callk"><code>lua_callk</code></a> with a non-null <code>k</code>.
- <p>
- Hook functions can yield under the following conditions:
- Only count and line events can yield
- and they cannot yield any value;
- to yield a hook function must finish its execution
- calling <a href="#lua_yield"><code>lua_yield</code></a> with <code>nresults</code> equal to zero.
- <hr><h3><a name="lua_sethook"><code>lua_sethook</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_sethook (lua_State *L, lua_Hook f, int mask, int count);</pre>
- <p>
- Sets the debugging hook function.
- <p>
- Argument <code>f</code> is the hook function.
- <code>mask</code> specifies on which events the hook will be called:
- it is formed by a bitwise or of the constants
- <a name="pdf-LUA_MASKCALL"><code>LUA_MASKCALL</code></a>,
- <a name="pdf-LUA_MASKRET"><code>LUA_MASKRET</code></a>,
- <a name="pdf-LUA_MASKLINE"><code>LUA_MASKLINE</code></a>,
- and <a name="pdf-LUA_MASKCOUNT"><code>LUA_MASKCOUNT</code></a>.
- The <code>count</code> argument is only meaningful when the mask
- includes <code>LUA_MASKCOUNT</code>.
- For each event, the hook is called as explained below:
- <ul>
- <li><b>The call hook: </b> is called when the interpreter calls a function.
- The hook is called just after Lua enters the new function,
- before the function gets its arguments.
- </li>
- <li><b>The return hook: </b> is called when the interpreter returns from a function.
- The hook is called just before Lua leaves the function.
- There is no standard way to access the values
- to be returned by the function.
- </li>
- <li><b>The line hook: </b> is called when the interpreter is about to
- start the execution of a new line of code,
- or when it jumps back in the code (even to the same line).
- (This event only happens while Lua is executing a Lua function.)
- </li>
- <li><b>The count hook: </b> is called after the interpreter executes every
- <code>count</code> instructions.
- (This event only happens while Lua is executing a Lua function.)
- </li>
- </ul>
- <p>
- A hook is disabled by setting <code>mask</code> to zero.
- <hr><h3><a name="lua_setlocal"><code>lua_setlocal</code></a></h3><p>
- <span class="apii">[-(0|1), +0, –]</span>
- <pre>const char *lua_setlocal (lua_State *L, lua_Debug *ar, int n);</pre>
- <p>
- Sets the value of a local variable of a given activation record.
- Parameters <code>ar</code> and <code>n</code> are as in <a href="#lua_getlocal"><code>lua_getlocal</code></a>
- (see <a href="#lua_getlocal"><code>lua_getlocal</code></a>).
- <a href="#lua_setlocal"><code>lua_setlocal</code></a> assigns the value at the top of the stack
- to the variable and returns its name.
- It also pops the value from the stack.
- <p>
- Returns <code>NULL</code> (and pops nothing)
- when the index is greater than
- the number of active local variables.
- <hr><h3><a name="lua_setupvalue"><code>lua_setupvalue</code></a></h3><p>
- <span class="apii">[-(0|1), +0, –]</span>
- <pre>const char *lua_setupvalue (lua_State *L, int funcindex, int n);</pre>
- <p>
- Sets the value of a closure's upvalue.
- It assigns the value at the top of the stack
- to the upvalue and returns its name.
- It also pops the value from the stack.
- Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>
- (see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>).
- <p>
- Returns <code>NULL</code> (and pops nothing)
- when the index is greater than the number of upvalues.
- <hr><h3><a name="lua_upvalueid"><code>lua_upvalueid</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void *lua_upvalueid (lua_State *L, int funcindex, int n);</pre>
- <p>
- Returns an unique identifier for the upvalue numbered <code>n</code>
- from the closure at index <code>funcindex</code>.
- Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>
- (see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>)
- (but <code>n</code> cannot be greater than the number of upvalues).
- <p>
- These unique identifiers allow a program to check whether different
- closures share upvalues.
- Lua closures that share an upvalue
- (that is, that access a same external local variable)
- will return identical ids for those upvalue indices.
- <hr><h3><a name="lua_upvaluejoin"><code>lua_upvaluejoin</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void lua_upvaluejoin (lua_State *L, int funcindex1, int n1,
- int funcindex2, int n2);</pre>
- <p>
- Make the <code>n1</code>-th upvalue of the Lua closure at index <code>funcindex1</code>
- refer to the <code>n2</code>-th upvalue of the Lua closure at index <code>funcindex2</code>.
- <h1>5 – <a name="5">The Auxiliary Library</a></h1>
- <p>
- The <em>auxiliary library</em> provides several convenient functions
- to interface C with Lua.
- While the basic API provides the primitive functions for all
- interactions between C and Lua,
- the auxiliary library provides higher-level functions for some
- common tasks.
- <p>
- All functions and types from the auxiliary library
- are defined in header file <code>lauxlib.h</code> and
- have a prefix <code>luaL_</code>.
- <p>
- All functions in the auxiliary library are built on
- top of the basic API,
- and so they provide nothing that cannot be done with that API.
- Nevertheless, the use of the auxiliary library ensures
- more consistency to your code.
- <p>
- Several functions in the auxiliary library use internally some
- extra stack slots.
- When a function in the auxiliary library uses less than five slots,
- it does not check the stack size;
- it simply assumes that there are enough slots.
- <p>
- Several functions in the auxiliary library are used to
- check C function arguments.
- Because the error message is formatted for arguments
- (e.g., "<code>bad argument #1</code>"),
- you should not use these functions for other stack values.
- <p>
- Functions called <code>luaL_check*</code>
- always throw an error if the check is not satisfied.
- <h2>5.1 – <a name="5.1">Functions and Types</a></h2>
- <p>
- Here we list all functions and types from the auxiliary library
- in alphabetical order.
- <hr><h3><a name="luaL_addchar"><code>luaL_addchar</code></a></h3><p>
- <span class="apii">[-?, +?, <em>e</em>]</span>
- <pre>void luaL_addchar (luaL_Buffer *B, char c);</pre>
- <p>
- Adds the byte <code>c</code> to the buffer <code>B</code>
- (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
- <hr><h3><a name="luaL_addlstring"><code>luaL_addlstring</code></a></h3><p>
- <span class="apii">[-?, +?, <em>e</em>]</span>
- <pre>void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);</pre>
- <p>
- Adds the string pointed to by <code>s</code> with length <code>l</code> to
- the buffer <code>B</code>
- (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
- The string can contain embedded zeros.
- <hr><h3><a name="luaL_addsize"><code>luaL_addsize</code></a></h3><p>
- <span class="apii">[-?, +?, <em>e</em>]</span>
- <pre>void luaL_addsize (luaL_Buffer *B, size_t n);</pre>
- <p>
- Adds to the buffer <code>B</code> (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>)
- a string of length <code>n</code> previously copied to the
- buffer area (see <a href="#luaL_prepbuffer"><code>luaL_prepbuffer</code></a>).
- <hr><h3><a name="luaL_addstring"><code>luaL_addstring</code></a></h3><p>
- <span class="apii">[-?, +?, <em>e</em>]</span>
- <pre>void luaL_addstring (luaL_Buffer *B, const char *s);</pre>
- <p>
- Adds the zero-terminated string pointed to by <code>s</code>
- to the buffer <code>B</code>
- (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
- The string cannot contain embedded zeros.
- <hr><h3><a name="luaL_addvalue"><code>luaL_addvalue</code></a></h3><p>
- <span class="apii">[-1, +?, <em>e</em>]</span>
- <pre>void luaL_addvalue (luaL_Buffer *B);</pre>
- <p>
- Adds the value at the top of the stack
- to the buffer <code>B</code>
- (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
- Pops the value.
- <p>
- This is the only function on string buffers that can (and must)
- be called with an extra element on the stack,
- which is the value to be added to the buffer.
- <hr><h3><a name="luaL_argcheck"><code>luaL_argcheck</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>void luaL_argcheck (lua_State *L,
- int cond,
- int arg,
- const char *extramsg);</pre>
- <p>
- Checks whether <code>cond</code> is true.
- If not, raises an error with a standard message.
- <hr><h3><a name="luaL_argerror"><code>luaL_argerror</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>int luaL_argerror (lua_State *L, int arg, const char *extramsg);</pre>
- <p>
- Raises an error with a standard message
- that includes <code>extramsg</code> as a comment.
- <p>
- This function never returns,
- but it is an idiom to use it in C functions
- as <code>return luaL_argerror(<em>args</em>)</code>.
- <hr><h3><a name="luaL_Buffer"><code>luaL_Buffer</code></a></h3>
- <pre>typedef struct luaL_Buffer luaL_Buffer;</pre>
- <p>
- Type for a <em>string buffer</em>.
- <p>
- A string buffer allows C code to build Lua strings piecemeal.
- Its pattern of use is as follows:
- <ul>
- <li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li>
- <li>Then initialize it with a call <code>luaL_buffinit(L, &b)</code>.</li>
- <li>
- Then add string pieces to the buffer calling any of
- the <code>luaL_add*</code> functions.
- </li>
- <li>
- Finish by calling <code>luaL_pushresult(&b)</code>.
- This call leaves the final string on the top of the stack.
- </li>
- </ul>
- <p>
- If you know beforehand the total size of the resulting string,
- you can use the buffer like this:
- <ul>
- <li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li>
- <li>Then initialize it and preallocate a space of
- size <code>sz</code> with a call <code>luaL_buffinitsize(L, &b, sz)</code>.</li>
- <li>Then copy the string into that space.</li>
- <li>
- Finish by calling <code>luaL_pushresultsize(&b, sz)</code>,
- where <code>sz</code> is the total size of the resulting string
- copied into that space.
- </li>
- </ul>
- <p>
- During its normal operation,
- a string buffer uses a variable number of stack slots.
- So, while using a buffer, you cannot assume that you know where
- the top of the stack is.
- You can use the stack between successive calls to buffer operations
- as long as that use is balanced;
- that is,
- when you call a buffer operation,
- the stack is at the same level
- it was immediately after the previous buffer operation.
- (The only exception to this rule is <a href="#luaL_addvalue"><code>luaL_addvalue</code></a>.)
- After calling <a href="#luaL_pushresult"><code>luaL_pushresult</code></a> the stack is back to its
- level when the buffer was initialized,
- plus the final string on its top.
- <hr><h3><a name="luaL_buffinit"><code>luaL_buffinit</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void luaL_buffinit (lua_State *L, luaL_Buffer *B);</pre>
- <p>
- Initializes a buffer <code>B</code>.
- This function does not allocate any space;
- the buffer must be declared as a variable
- (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
- <hr><h3><a name="luaL_buffinitsize"><code>luaL_buffinitsize</code></a></h3><p>
- <span class="apii">[-?, +?, <em>e</em>]</span>
- <pre>char *luaL_buffinitsize (lua_State *L, luaL_Buffer *B, size_t sz);</pre>
- <p>
- Equivalent to the sequence
- <a href="#luaL_buffinit"><code>luaL_buffinit</code></a>, <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a>.
- <hr><h3><a name="luaL_callmeta"><code>luaL_callmeta</code></a></h3><p>
- <span class="apii">[-0, +(0|1), <em>e</em>]</span>
- <pre>int luaL_callmeta (lua_State *L, int obj, const char *e);</pre>
- <p>
- Calls a metamethod.
- <p>
- If the object at index <code>obj</code> has a metatable and this
- metatable has a field <code>e</code>,
- this function calls this field passing the object as its only argument.
- In this case this function returns true and pushes onto the
- stack the value returned by the call.
- If there is no metatable or no metamethod,
- this function returns false (without pushing any value on the stack).
- <hr><h3><a name="luaL_checkany"><code>luaL_checkany</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>void luaL_checkany (lua_State *L, int arg);</pre>
- <p>
- Checks whether the function has an argument
- of any type (including <b>nil</b>) at position <code>arg</code>.
- <hr><h3><a name="luaL_checkint"><code>luaL_checkint</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>int luaL_checkint (lua_State *L, int arg);</pre>
- <p>
- Checks whether the function argument <code>arg</code> is a number
- and returns this number cast to an <code>int</code>.
- <hr><h3><a name="luaL_checkinteger"><code>luaL_checkinteger</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>lua_Integer luaL_checkinteger (lua_State *L, int arg);</pre>
- <p>
- Checks whether the function argument <code>arg</code> is a number
- and returns this number cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>.
- <hr><h3><a name="luaL_checklong"><code>luaL_checklong</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>long luaL_checklong (lua_State *L, int arg);</pre>
- <p>
- Checks whether the function argument <code>arg</code> is a number
- and returns this number cast to a <code>long</code>.
- <hr><h3><a name="luaL_checklstring"><code>luaL_checklstring</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>const char *luaL_checklstring (lua_State *L, int arg, size_t *l);</pre>
- <p>
- Checks whether the function argument <code>arg</code> is a string
- and returns this string;
- if <code>l</code> is not <code>NULL</code> fills <code>*l</code>
- with the string's length.
- <p>
- This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result,
- so all conversions and caveats of that function apply here.
- <hr><h3><a name="luaL_checknumber"><code>luaL_checknumber</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>lua_Number luaL_checknumber (lua_State *L, int arg);</pre>
- <p>
- Checks whether the function argument <code>arg</code> is a number
- and returns this number.
- <hr><h3><a name="luaL_checkoption"><code>luaL_checkoption</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>int luaL_checkoption (lua_State *L,
- int arg,
- const char *def,
- const char *const lst[]);</pre>
- <p>
- Checks whether the function argument <code>arg</code> is a string and
- searches for this string in the array <code>lst</code>
- (which must be NULL-terminated).
- Returns the index in the array where the string was found.
- Raises an error if the argument is not a string or
- if the string cannot be found.
- <p>
- If <code>def</code> is not <code>NULL</code>,
- the function uses <code>def</code> as a default value when
- there is no argument <code>arg</code> or when this argument is <b>nil</b>.
- <p>
- This is a useful function for mapping strings to C enums.
- (The usual convention in Lua libraries is
- to use strings instead of numbers to select options.)
- <hr><h3><a name="luaL_checkstack"><code>luaL_checkstack</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>void luaL_checkstack (lua_State *L, int sz, const char *msg);</pre>
- <p>
- Grows the stack size to <code>top + sz</code> elements,
- raising an error if the stack cannot grow to that size.
- <code>msg</code> is an additional text to go into the error message
- (or <code>NULL</code> for no additional text).
- <hr><h3><a name="luaL_checkstring"><code>luaL_checkstring</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>const char *luaL_checkstring (lua_State *L, int arg);</pre>
- <p>
- Checks whether the function argument <code>arg</code> is a string
- and returns this string.
- <p>
- This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result,
- so all conversions and caveats of that function apply here.
- <hr><h3><a name="luaL_checktype"><code>luaL_checktype</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>void luaL_checktype (lua_State *L, int arg, int t);</pre>
- <p>
- Checks whether the function argument <code>arg</code> has type <code>t</code>.
- See <a href="#lua_type"><code>lua_type</code></a> for the encoding of types for <code>t</code>.
- <hr><h3><a name="luaL_checkudata"><code>luaL_checkudata</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>void *luaL_checkudata (lua_State *L, int arg, const char *tname);</pre>
- <p>
- Checks whether the function argument <code>arg</code> is a userdata
- of the type <code>tname</code> (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>) and
- returns the userdata address (see <a href="#lua_touserdata"><code>lua_touserdata</code></a>).
- <hr><h3><a name="luaL_checkunsigned"><code>luaL_checkunsigned</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>lua_Unsigned luaL_checkunsigned (lua_State *L, int arg);</pre>
- <p>
- Checks whether the function argument <code>arg</code> is a number
- and returns this number cast to a <a href="#lua_Unsigned"><code>lua_Unsigned</code></a>.
- <hr><h3><a name="luaL_checkversion"><code>luaL_checkversion</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void luaL_checkversion (lua_State *L);</pre>
- <p>
- Checks whether the core running the call,
- the core that created the Lua state,
- and the code making the call are all using the same version of Lua.
- Also checks whether the core running the call
- and the core that created the Lua state
- are using the same address space.
- <hr><h3><a name="luaL_dofile"><code>luaL_dofile</code></a></h3><p>
- <span class="apii">[-0, +?, <em>e</em>]</span>
- <pre>int luaL_dofile (lua_State *L, const char *filename);</pre>
- <p>
- Loads and runs the given file.
- It is defined as the following macro:
- <pre>
- (luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0))
- </pre><p>
- It returns false if there are no errors
- or true in case of errors.
- <hr><h3><a name="luaL_dostring"><code>luaL_dostring</code></a></h3><p>
- <span class="apii">[-0, +?, –]</span>
- <pre>int luaL_dostring (lua_State *L, const char *str);</pre>
- <p>
- Loads and runs the given string.
- It is defined as the following macro:
- <pre>
- (luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0))
- </pre><p>
- It returns false if there are no errors
- or true in case of errors.
- <hr><h3><a name="luaL_error"><code>luaL_error</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>int luaL_error (lua_State *L, const char *fmt, ...);</pre>
- <p>
- Raises an error.
- The error message format is given by <code>fmt</code>
- plus any extra arguments,
- following the same rules of <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>.
- It also adds at the beginning of the message the file name and
- the line number where the error occurred,
- if this information is available.
- <p>
- This function never returns,
- but it is an idiom to use it in C functions
- as <code>return luaL_error(<em>args</em>)</code>.
- <hr><h3><a name="luaL_execresult"><code>luaL_execresult</code></a></h3><p>
- <span class="apii">[-0, +3, <em>e</em>]</span>
- <pre>int luaL_execresult (lua_State *L, int stat);</pre>
- <p>
- This function produces the return values for
- process-related functions in the standard library
- (<a href="#pdf-os.execute"><code>os.execute</code></a> and <a href="#pdf-io.close"><code>io.close</code></a>).
- <hr><h3><a name="luaL_fileresult"><code>luaL_fileresult</code></a></h3><p>
- <span class="apii">[-0, +(1|3), <em>e</em>]</span>
- <pre>int luaL_fileresult (lua_State *L, int stat, const char *fname);</pre>
- <p>
- This function produces the return values for
- file-related functions in the standard library
- (<a href="#pdf-io.open"><code>io.open</code></a>, <a href="#pdf-os.rename"><code>os.rename</code></a>, <a href="#pdf-file:seek"><code>file:seek</code></a>, etc.).
- <hr><h3><a name="luaL_getmetafield"><code>luaL_getmetafield</code></a></h3><p>
- <span class="apii">[-0, +(0|1), <em>e</em>]</span>
- <pre>int luaL_getmetafield (lua_State *L, int obj, const char *e);</pre>
- <p>
- Pushes onto the stack the field <code>e</code> from the metatable
- of the object at index <code>obj</code>.
- If the object does not have a metatable,
- or if the metatable does not have this field,
- returns false and pushes nothing.
- <hr><h3><a name="luaL_getmetatable"><code>luaL_getmetatable</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void luaL_getmetatable (lua_State *L, const char *tname);</pre>
- <p>
- Pushes onto the stack the metatable associated with name <code>tname</code>
- in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>).
- <hr><h3><a name="luaL_getsubtable"><code>luaL_getsubtable</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>int luaL_getsubtable (lua_State *L, int idx, const char *fname);</pre>
- <p>
- Ensures that the value <code>t[fname]</code>,
- where <code>t</code> is the value at index <code>idx</code>,
- is a table,
- and pushes that table onto the stack.
- Returns true if it finds a previous table there
- and false if it creates a new table.
- <hr><h3><a name="luaL_gsub"><code>luaL_gsub</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>const char *luaL_gsub (lua_State *L,
- const char *s,
- const char *p,
- const char *r);</pre>
- <p>
- Creates a copy of string <code>s</code> by replacing
- any occurrence of the string <code>p</code>
- with the string <code>r</code>.
- Pushes the resulting string on the stack and returns it.
- <hr><h3><a name="luaL_len"><code>luaL_len</code></a></h3><p>
- <span class="apii">[-0, +0, <em>e</em>]</span>
- <pre>int luaL_len (lua_State *L, int index);</pre>
- <p>
- Returns the "length" of the value at the given index
- as a number;
- it is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.6">§3.4.6</a>).
- Raises an error if the result of the operation is not a number.
- (This case only can happen through metamethods.)
- <hr><h3><a name="luaL_loadbuffer"><code>luaL_loadbuffer</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>int luaL_loadbuffer (lua_State *L,
- const char *buff,
- size_t sz,
- const char *name);</pre>
- <p>
- Equivalent to <a href="#luaL_loadbufferx"><code>luaL_loadbufferx</code></a> with <code>mode</code> equal to <code>NULL</code>.
- <hr><h3><a name="luaL_loadbufferx"><code>luaL_loadbufferx</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>int luaL_loadbufferx (lua_State *L,
- const char *buff,
- size_t sz,
- const char *name,
- const char *mode);</pre>
- <p>
- Loads a buffer as a Lua chunk.
- This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the
- buffer pointed to by <code>buff</code> with size <code>sz</code>.
- <p>
- This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>.
- <code>name</code> is the chunk name,
- used for debug information and error messages.
- The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>.
- <hr><h3><a name="luaL_loadfile"><code>luaL_loadfile</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>int luaL_loadfile (lua_State *L, const char *filename);</pre>
- <p>
- Equivalent to <a href="#luaL_loadfilex"><code>luaL_loadfilex</code></a> with <code>mode</code> equal to <code>NULL</code>.
- <hr><h3><a name="luaL_loadfilex"><code>luaL_loadfilex</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>int luaL_loadfilex (lua_State *L, const char *filename,
- const char *mode);</pre>
- <p>
- Loads a file as a Lua chunk.
- This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the file
- named <code>filename</code>.
- If <code>filename</code> is <code>NULL</code>,
- then it loads from the standard input.
- The first line in the file is ignored if it starts with a <code>#</code>.
- <p>
- The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>.
- <p>
- This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>,
- but it has an extra error code <a name="pdf-LUA_ERRFILE"><code>LUA_ERRFILE</code></a>
- if it cannot open/read the file or the file has a wrong mode.
- <p>
- As <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk;
- it does not run it.
- <hr><h3><a name="luaL_loadstring"><code>luaL_loadstring</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>int luaL_loadstring (lua_State *L, const char *s);</pre>
- <p>
- Loads a string as a Lua chunk.
- This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in
- the zero-terminated string <code>s</code>.
- <p>
- This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>.
- <p>
- Also as <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk;
- it does not run it.
- <hr><h3><a name="luaL_newlib"><code>luaL_newlib</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>void luaL_newlib (lua_State *L, const luaL_Reg *l);</pre>
- <p>
- Creates a new table and registers there
- the functions in list <code>l</code>.
- It is implemented as the following macro:
- <pre>
- (luaL_newlibtable(L,l), luaL_setfuncs(L,l,0))
- </pre>
- <hr><h3><a name="luaL_newlibtable"><code>luaL_newlibtable</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>void luaL_newlibtable (lua_State *L, const luaL_Reg l[]);</pre>
- <p>
- Creates a new table with a size optimized
- to store all entries in the array <code>l</code>
- (but does not actually store them).
- It is intended to be used in conjunction with <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a>
- (see <a href="#luaL_newlib"><code>luaL_newlib</code></a>).
- <p>
- It is implemented as a macro.
- The array <code>l</code> must be the actual array,
- not a pointer to it.
- <hr><h3><a name="luaL_newmetatable"><code>luaL_newmetatable</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>int luaL_newmetatable (lua_State *L, const char *tname);</pre>
- <p>
- If the registry already has the key <code>tname</code>,
- returns 0.
- Otherwise,
- creates a new table to be used as a metatable for userdata,
- adds it to the registry with key <code>tname</code>,
- and returns 1.
- <p>
- In both cases pushes onto the stack the final value associated
- with <code>tname</code> in the registry.
- <hr><h3><a name="luaL_newstate"><code>luaL_newstate</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_State *luaL_newstate (void);</pre>
- <p>
- Creates a new Lua state.
- It calls <a href="#lua_newstate"><code>lua_newstate</code></a> with an
- allocator based on the standard C <code>realloc</code> function
- and then sets a panic function (see <a href="#4.6">§4.6</a>) that prints
- an error message to the standard error output in case of fatal
- errors.
- <p>
- Returns the new state,
- or <code>NULL</code> if there is a memory allocation error.
- <hr><h3><a name="luaL_openlibs"><code>luaL_openlibs</code></a></h3><p>
- <span class="apii">[-0, +0, <em>e</em>]</span>
- <pre>void luaL_openlibs (lua_State *L);</pre>
- <p>
- Opens all standard Lua libraries into the given state.
- <hr><h3><a name="luaL_optint"><code>luaL_optint</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>int luaL_optint (lua_State *L, int arg, int d);</pre>
- <p>
- If the function argument <code>arg</code> is a number,
- returns this number cast to an <code>int</code>.
- If this argument is absent or is <b>nil</b>,
- returns <code>d</code>.
- Otherwise, raises an error.
- <hr><h3><a name="luaL_optinteger"><code>luaL_optinteger</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>lua_Integer luaL_optinteger (lua_State *L,
- int arg,
- lua_Integer d);</pre>
- <p>
- If the function argument <code>arg</code> is a number,
- returns this number cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>.
- If this argument is absent or is <b>nil</b>,
- returns <code>d</code>.
- Otherwise, raises an error.
- <hr><h3><a name="luaL_optlong"><code>luaL_optlong</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>long luaL_optlong (lua_State *L, int arg, long d);</pre>
- <p>
- If the function argument <code>arg</code> is a number,
- returns this number cast to a <code>long</code>.
- If this argument is absent or is <b>nil</b>,
- returns <code>d</code>.
- Otherwise, raises an error.
- <hr><h3><a name="luaL_optlstring"><code>luaL_optlstring</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>const char *luaL_optlstring (lua_State *L,
- int arg,
- const char *d,
- size_t *l);</pre>
- <p>
- If the function argument <code>arg</code> is a string,
- returns this string.
- If this argument is absent or is <b>nil</b>,
- returns <code>d</code>.
- Otherwise, raises an error.
- <p>
- If <code>l</code> is not <code>NULL</code>,
- fills the position <code>*l</code> with the result's length.
- <hr><h3><a name="luaL_optnumber"><code>luaL_optnumber</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>lua_Number luaL_optnumber (lua_State *L, int arg, lua_Number d);</pre>
- <p>
- If the function argument <code>arg</code> is a number,
- returns this number.
- If this argument is absent or is <b>nil</b>,
- returns <code>d</code>.
- Otherwise, raises an error.
- <hr><h3><a name="luaL_optstring"><code>luaL_optstring</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>const char *luaL_optstring (lua_State *L,
- int arg,
- const char *d);</pre>
- <p>
- If the function argument <code>arg</code> is a string,
- returns this string.
- If this argument is absent or is <b>nil</b>,
- returns <code>d</code>.
- Otherwise, raises an error.
- <hr><h3><a name="luaL_optunsigned"><code>luaL_optunsigned</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>lua_Unsigned luaL_optunsigned (lua_State *L,
- int arg,
- lua_Unsigned u);</pre>
- <p>
- If the function argument <code>arg</code> is a number,
- returns this number cast to a <a href="#lua_Unsigned"><code>lua_Unsigned</code></a>.
- If this argument is absent or is <b>nil</b>,
- returns <code>u</code>.
- Otherwise, raises an error.
- <hr><h3><a name="luaL_prepbuffer"><code>luaL_prepbuffer</code></a></h3><p>
- <span class="apii">[-?, +?, <em>e</em>]</span>
- <pre>char *luaL_prepbuffer (luaL_Buffer *B);</pre>
- <p>
- Equivalent to <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a>
- with the predefined size <a name="pdf-LUAL_BUFFERSIZE"><code>LUAL_BUFFERSIZE</code></a>.
- <hr><h3><a name="luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a></h3><p>
- <span class="apii">[-?, +?, <em>e</em>]</span>
- <pre>char *luaL_prepbuffsize (luaL_Buffer *B, size_t sz);</pre>
- <p>
- Returns an address to a space of size <code>sz</code>
- where you can copy a string to be added to buffer <code>B</code>
- (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
- After copying the string into this space you must call
- <a href="#luaL_addsize"><code>luaL_addsize</code></a> with the size of the string to actually add
- it to the buffer.
- <hr><h3><a name="luaL_pushresult"><code>luaL_pushresult</code></a></h3><p>
- <span class="apii">[-?, +1, <em>e</em>]</span>
- <pre>void luaL_pushresult (luaL_Buffer *B);</pre>
- <p>
- Finishes the use of buffer <code>B</code> leaving the final string on
- the top of the stack.
- <hr><h3><a name="luaL_pushresultsize"><code>luaL_pushresultsize</code></a></h3><p>
- <span class="apii">[-?, +1, <em>e</em>]</span>
- <pre>void luaL_pushresultsize (luaL_Buffer *B, size_t sz);</pre>
- <p>
- Equivalent to the sequence <a href="#luaL_addsize"><code>luaL_addsize</code></a>, <a href="#luaL_pushresult"><code>luaL_pushresult</code></a>.
- <hr><h3><a name="luaL_ref"><code>luaL_ref</code></a></h3><p>
- <span class="apii">[-1, +0, <em>e</em>]</span>
- <pre>int luaL_ref (lua_State *L, int t);</pre>
- <p>
- Creates and returns a <em>reference</em>,
- in the table at index <code>t</code>,
- for the object at the top of the stack (and pops the object).
- <p>
- A reference is a unique integer key.
- As long as you do not manually add integer keys into table <code>t</code>,
- <a href="#luaL_ref"><code>luaL_ref</code></a> ensures the uniqueness of the key it returns.
- You can retrieve an object referred by reference <code>r</code>
- by calling <code>lua_rawgeti(L, t, r)</code>.
- Function <a href="#luaL_unref"><code>luaL_unref</code></a> frees a reference and its associated object.
- <p>
- If the object at the top of the stack is <b>nil</b>,
- <a href="#luaL_ref"><code>luaL_ref</code></a> returns the constant <a name="pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>.
- The constant <a name="pdf-LUA_NOREF"><code>LUA_NOREF</code></a> is guaranteed to be different
- from any reference returned by <a href="#luaL_ref"><code>luaL_ref</code></a>.
- <hr><h3><a name="luaL_Reg"><code>luaL_Reg</code></a></h3>
- <pre>typedef struct luaL_Reg {
- const char *name;
- lua_CFunction func;
- } luaL_Reg;</pre>
- <p>
- Type for arrays of functions to be registered by
- <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a>.
- <code>name</code> is the function name and <code>func</code> is a pointer to
- the function.
- Any array of <a href="#luaL_Reg"><code>luaL_Reg</code></a> must end with an sentinel entry
- in which both <code>name</code> and <code>func</code> are <code>NULL</code>.
- <hr><h3><a name="luaL_requiref"><code>luaL_requiref</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>void luaL_requiref (lua_State *L, const char *modname,
- lua_CFunction openf, int glb);</pre>
- <p>
- Calls function <code>openf</code> with string <code>modname</code> as an argument
- and sets the call result in <code>package.loaded[modname]</code>,
- as if that function has been called through <a href="#pdf-require"><code>require</code></a>.
- <p>
- If <code>glb</code> is true,
- also stores the result into global <code>modname</code>.
- <p>
- Leaves a copy of that result on the stack.
- <hr><h3><a name="luaL_setfuncs"><code>luaL_setfuncs</code></a></h3><p>
- <span class="apii">[-nup, +0, <em>e</em>]</span>
- <pre>void luaL_setfuncs (lua_State *L, const luaL_Reg *l, int nup);</pre>
- <p>
- Registers all functions in the array <code>l</code>
- (see <a href="#luaL_Reg"><code>luaL_Reg</code></a>) into the table on the top of the stack
- (below optional upvalues, see next).
- <p>
- When <code>nup</code> is not zero,
- all functions are created sharing <code>nup</code> upvalues,
- which must be previously pushed on the stack
- on top of the library table.
- These values are popped from the stack after the registration.
- <hr><h3><a name="luaL_setmetatable"><code>luaL_setmetatable</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void luaL_setmetatable (lua_State *L, const char *tname);</pre>
- <p>
- Sets the metatable of the object at the top of the stack
- as the metatable associated with name <code>tname</code>
- in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>).
- <hr><h3><a name="luaL_testudata"><code>luaL_testudata</code></a></h3><p>
- <span class="apii">[-0, +0, <em>e</em>]</span>
- <pre>void *luaL_testudata (lua_State *L, int arg, const char *tname);</pre>
- <p>
- This function works like <a href="#luaL_checkudata"><code>luaL_checkudata</code></a>,
- except that, when the test fails,
- it returns <code>NULL</code> instead of throwing an error.
- <hr><h3><a name="luaL_tolstring"><code>luaL_tolstring</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>const char *luaL_tolstring (lua_State *L, int idx, size_t *len);</pre>
- <p>
- Converts any Lua value at the given index to a C string
- in a reasonable format.
- The resulting string is pushed onto the stack and also
- returned by the function.
- If <code>len</code> is not <code>NULL</code>,
- the function also sets <code>*len</code> with the string length.
- <p>
- If the value has a metatable with a <code>"__tostring"</code> field,
- then <code>luaL_tolstring</code> calls the corresponding metamethod
- with the value as argument,
- and uses the result of the call as its result.
- <hr><h3><a name="luaL_traceback"><code>luaL_traceback</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>void luaL_traceback (lua_State *L, lua_State *L1, const char *msg,
- int level);</pre>
- <p>
- Creates and pushes a traceback of the stack <code>L1</code>.
- If <code>msg</code> is not <code>NULL</code> it is appended
- at the beginning of the traceback.
- The <code>level</code> parameter tells at which level
- to start the traceback.
- <hr><h3><a name="luaL_typename"><code>luaL_typename</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>const char *luaL_typename (lua_State *L, int index);</pre>
- <p>
- Returns the name of the type of the value at the given index.
- <hr><h3><a name="luaL_unref"><code>luaL_unref</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void luaL_unref (lua_State *L, int t, int ref);</pre>
- <p>
- Releases reference <code>ref</code> from the table at index <code>t</code>
- (see <a href="#luaL_ref"><code>luaL_ref</code></a>).
- The entry is removed from the table,
- so that the referred object can be collected.
- The reference <code>ref</code> is also freed to be used again.
- <p>
- If <code>ref</code> is <a href="#pdf-LUA_NOREF"><code>LUA_NOREF</code></a> or <a href="#pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>,
- <a href="#luaL_unref"><code>luaL_unref</code></a> does nothing.
- <hr><h3><a name="luaL_where"><code>luaL_where</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>void luaL_where (lua_State *L, int lvl);</pre>
- <p>
- Pushes onto the stack a string identifying the current position
- of the control at level <code>lvl</code> in the call stack.
- Typically this string has the following format:
- <pre>
- <em>chunkname</em>:<em>currentline</em>:
- </pre><p>
- Level 0 is the running function,
- level 1 is the function that called the running function,
- etc.
- <p>
- This function is used to build a prefix for error messages.
- <h1>6 – <a name="6">Standard Libraries</a></h1>
- <p>
- The standard Lua libraries provide useful functions
- that are implemented directly through the C API.
- Some of these functions provide essential services to the language
- (e.g., <a href="#pdf-type"><code>type</code></a> and <a href="#pdf-getmetatable"><code>getmetatable</code></a>);
- others provide access to "outside" services (e.g., I/O);
- and others could be implemented in Lua itself,
- but are quite useful or have critical performance requirements that
- deserve an implementation in C (e.g., <a href="#pdf-table.sort"><code>table.sort</code></a>).
- <p>
- All libraries are implemented through the official C API
- and are provided as separate C modules.
- Currently, Lua has the following standard libraries:
- <ul>
- <li>basic library (<a href="#6.1">§6.1</a>);</li>
- <li>coroutine library (<a href="#6.2">§6.2</a>);</li>
- <li>package library (<a href="#6.3">§6.3</a>);</li>
- <li>string manipulation (<a href="#6.4">§6.4</a>);</li>
- <li>table manipulation (<a href="#6.5">§6.5</a>);</li>
- <li>mathematical functions (<a href="#6.6">§6.6</a>) (sin, log, etc.);</li>
- <li>bitwise operations (<a href="#6.7">§6.7</a>);</li>
- <li>input and output (<a href="#6.8">§6.8</a>);</li>
- <li>operating system facilities (<a href="#6.9">§6.9</a>);</li>
- <li>debug facilities (<a href="#6.10">§6.10</a>).</li>
- </ul><p>
- Except for the basic and the package libraries,
- each library provides all its functions as fields of a global table
- or as methods of its objects.
- <p>
- To have access to these libraries,
- the C host program should call the <a href="#luaL_openlibs"><code>luaL_openlibs</code></a> function,
- which opens all standard libraries.
- Alternatively,
- the host program can open them individually by using
- <a href="#luaL_requiref"><code>luaL_requiref</code></a> to call
- <a name="pdf-luaopen_base"><code>luaopen_base</code></a> (for the basic library),
- <a name="pdf-luaopen_package"><code>luaopen_package</code></a> (for the package library),
- <a name="pdf-luaopen_coroutine"><code>luaopen_coroutine</code></a> (for the coroutine library),
- <a name="pdf-luaopen_string"><code>luaopen_string</code></a> (for the string library),
- <a name="pdf-luaopen_table"><code>luaopen_table</code></a> (for the table library),
- <a name="pdf-luaopen_math"><code>luaopen_math</code></a> (for the mathematical library),
- <a name="pdf-luaopen_bit32"><code>luaopen_bit32</code></a> (for the bit library),
- <a name="pdf-luaopen_io"><code>luaopen_io</code></a> (for the I/O library),
- <a name="pdf-luaopen_os"><code>luaopen_os</code></a> (for the Operating System library),
- and <a name="pdf-luaopen_debug"><code>luaopen_debug</code></a> (for the debug library).
- These functions are declared in <a name="pdf-lualib.h"><code>lualib.h</code></a>.
- <h2>6.1 – <a name="6.1">Basic Functions</a></h2>
- <p>
- The basic library provides core functions to Lua.
- If you do not include this library in your application,
- you should check carefully whether you need to provide
- implementations for some of its facilities.
- <p>
- <hr><h3><a name="pdf-assert"><code>assert (v [, message])</code></a></h3>
- Issues an error when
- the value of its argument <code>v</code> is false (i.e., <b>nil</b> or <b>false</b>);
- otherwise, returns all its arguments.
- <code>message</code> is an error message;
- when absent, it defaults to "assertion failed!"
- <p>
- <hr><h3><a name="pdf-collectgarbage"><code>collectgarbage ([opt [, arg]])</code></a></h3>
- <p>
- This function is a generic interface to the garbage collector.
- It performs different functions according to its first argument, <code>opt</code>:
- <ul>
- <li><b>"<code>collect</code>": </b>
- performs a full garbage-collection cycle.
- This is the default option.
- </li>
- <li><b>"<code>stop</code>": </b>
- stops automatic execution of the garbage collector.
- The collector will run only when explicitly invoked,
- until a call to restart it.
- </li>
- <li><b>"<code>restart</code>": </b>
- restarts automatic execution of the garbage collector.
- </li>
- <li><b>"<code>count</code>": </b>
- returns the total memory in use by Lua (in Kbytes) and
- a second value with the total memory in bytes modulo 1024.
- The first value has a fractional part,
- so the following equality is always true:
- <pre>
- k, b = collectgarbage("count")
- assert(k*1024 == math.floor(k)*1024 + b)
- </pre><p>
- (The second result is useful when Lua is compiled
- with a non floating-point type for numbers.)
- </li>
- <li><b>"<code>step</code>": </b>
- performs a garbage-collection step.
- The step "size" is controlled by <code>arg</code>
- (larger values mean more steps) in a non-specified way.
- If you want to control the step size
- you must experimentally tune the value of <code>arg</code>.
- Returns <b>true</b> if the step finished a collection cycle.
- </li>
- <li><b>"<code>setpause</code>": </b>
- sets <code>arg</code> as the new value for the <em>pause</em> of
- the collector (see <a href="#2.5">§2.5</a>).
- Returns the previous value for <em>pause</em>.
- </li>
- <li><b>"<code>setstepmul</code>": </b>
- sets <code>arg</code> as the new value for the <em>step multiplier</em> of
- the collector (see <a href="#2.5">§2.5</a>).
- Returns the previous value for <em>step</em>.
- </li>
- <li><b>"<code>isrunning</code>": </b>
- returns a boolean that tells whether the collector is running
- (i.e., not stopped).
- </li>
- <li><b>"<code>generational</code>": </b>
- changes the collector to generational mode.
- This is an experimental feature (see <a href="#2.5">§2.5</a>).
- </li>
- <li><b>"<code>incremental</code>": </b>
- changes the collector to incremental mode.
- This is the default mode.
- </li>
- </ul>
- <p>
- <hr><h3><a name="pdf-dofile"><code>dofile ([filename])</code></a></h3>
- Opens the named file and executes its contents as a Lua chunk.
- When called without arguments,
- <code>dofile</code> executes the contents of the standard input (<code>stdin</code>).
- Returns all values returned by the chunk.
- In case of errors, <code>dofile</code> propagates the error
- to its caller (that is, <code>dofile</code> does not run in protected mode).
- <p>
- <hr><h3><a name="pdf-error"><code>error (message [, level])</code></a></h3>
- Terminates the last protected function called
- and returns <code>message</code> as the error message.
- Function <code>error</code> never returns.
- <p>
- Usually, <code>error</code> adds some information about the error position
- at the beginning of the message, if the message is a string.
- The <code>level</code> argument specifies how to get the error position.
- With level 1 (the default), the error position is where the
- <code>error</code> function was called.
- Level 2 points the error to where the function
- that called <code>error</code> was called; and so on.
- Passing a level 0 avoids the addition of error position information
- to the message.
- <p>
- <hr><h3><a name="pdf-_G"><code>_G</code></a></h3>
- A global variable (not a function) that
- holds the global environment (see <a href="#2.2">§2.2</a>).
- Lua itself does not use this variable;
- changing its value does not affect any environment,
- nor vice-versa.
- <p>
- <hr><h3><a name="pdf-getmetatable"><code>getmetatable (object)</code></a></h3>
- <p>
- If <code>object</code> does not have a metatable, returns <b>nil</b>.
- Otherwise,
- if the object's metatable has a <code>"__metatable"</code> field,
- returns the associated value.
- Otherwise, returns the metatable of the given object.
- <p>
- <hr><h3><a name="pdf-ipairs"><code>ipairs (t)</code></a></h3>
- <p>
- If <code>t</code> has a metamethod <code>__ipairs</code>,
- calls it with <code>t</code> as argument and returns the first three
- results from the call.
- <p>
- Otherwise,
- returns three values: an iterator function, the table <code>t</code>, and 0,
- so that the construction
- <pre>
- for i,v in ipairs(t) do <em>body</em> end
- </pre><p>
- will iterate over the pairs (<code>1,t[1]</code>), (<code>2,t[2]</code>), ...,
- up to the first integer key absent from the table.
- <p>
- <hr><h3><a name="pdf-load"><code>load (ld [, source [, mode [, env]]])</code></a></h3>
- <p>
- Loads a chunk.
- <p>
- If <code>ld</code> is a string, the chunk is this string.
- If <code>ld</code> is a function,
- <code>load</code> calls it repeatedly to get the chunk pieces.
- Each call to <code>ld</code> must return a string that concatenates
- with previous results.
- A return of an empty string, <b>nil</b>, or no value signals the end of the chunk.
- <p>
- If there are no syntactic errors,
- returns the compiled chunk as a function;
- otherwise, returns <b>nil</b> plus the error message.
- <p>
- If the resulting function has upvalues,
- the first upvalue is set to the value of <code>env</code>,
- if that parameter is given,
- or to the value of the global environment.
- (When you load a main chunk,
- the resulting function will always have exactly one upvalue,
- the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>).
- When you load a binary chunk created from a function (see <a href="#pdf-string.dump"><code>string.dump</code></a>),
- the resulting function can have arbitrary upvalues.)
- <p>
- <code>source</code> is used as the source of the chunk for error messages
- and debug information (see <a href="#4.9">§4.9</a>).
- When absent,
- it defaults to <code>ld</code>, if <code>ld</code> is a string,
- or to "<code>=(load)</code>" otherwise.
- <p>
- The string <code>mode</code> controls whether the chunk can be text or binary
- (that is, a precompiled chunk).
- It may be the string "<code>b</code>" (only binary chunks),
- "<code>t</code>" (only text chunks),
- or "<code>bt</code>" (both binary and text).
- The default is "<code>bt</code>".
- <p>
- <hr><h3><a name="pdf-loadfile"><code>loadfile ([filename [, mode [, env]]])</code></a></h3>
- <p>
- Similar to <a href="#pdf-load"><code>load</code></a>,
- but gets the chunk from file <code>filename</code>
- or from the standard input,
- if no file name is given.
- <p>
- <hr><h3><a name="pdf-next"><code>next (table [, index])</code></a></h3>
- <p>
- Allows a program to traverse all fields of a table.
- Its first argument is a table and its second argument
- is an index in this table.
- <code>next</code> returns the next index of the table
- and its associated value.
- When called with <b>nil</b> as its second argument,
- <code>next</code> returns an initial index
- and its associated value.
- When called with the last index,
- or with <b>nil</b> in an empty table,
- <code>next</code> returns <b>nil</b>.
- If the second argument is absent, then it is interpreted as <b>nil</b>.
- In particular,
- you can use <code>next(t)</code> to check whether a table is empty.
- <p>
- The order in which the indices are enumerated is not specified,
- <em>even for numeric indices</em>.
- (To traverse a table in numeric order,
- use a numerical <b>for</b>.)
- <p>
- The behavior of <code>next</code> is undefined if,
- during the traversal,
- you assign any value to a non-existent field in the table.
- You may however modify existing fields.
- In particular, you may clear existing fields.
- <p>
- <hr><h3><a name="pdf-pairs"><code>pairs (t)</code></a></h3>
- <p>
- If <code>t</code> has a metamethod <code>__pairs</code>,
- calls it with <code>t</code> as argument and returns the first three
- results from the call.
- <p>
- Otherwise,
- returns three values: the <a href="#pdf-next"><code>next</code></a> function, the table <code>t</code>, and <b>nil</b>,
- so that the construction
- <pre>
- for k,v in pairs(t) do <em>body</em> end
- </pre><p>
- will iterate over all key–value pairs of table <code>t</code>.
- <p>
- See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying
- the table during its traversal.
- <p>
- <hr><h3><a name="pdf-pcall"><code>pcall (f [, arg1, ···])</code></a></h3>
- <p>
- Calls function <code>f</code> with
- the given arguments in <em>protected mode</em>.
- This means that any error inside <code>f</code> is not propagated;
- instead, <code>pcall</code> catches the error
- and returns a status code.
- Its first result is the status code (a boolean),
- which is true if the call succeeds without errors.
- In such case, <code>pcall</code> also returns all results from the call,
- after this first result.
- In case of any error, <code>pcall</code> returns <b>false</b> plus the error message.
- <p>
- <hr><h3><a name="pdf-print"><code>print (···)</code></a></h3>
- Receives any number of arguments
- and prints their values to <code>stdout</code>,
- using the <a href="#pdf-tostring"><code>tostring</code></a> function to convert each argument to a string.
- <code>print</code> is not intended for formatted output,
- but only as a quick way to show a value,
- for instance for debugging.
- For complete control over the output,
- use <a href="#pdf-string.format"><code>string.format</code></a> and <a href="#pdf-io.write"><code>io.write</code></a>.
- <p>
- <hr><h3><a name="pdf-rawequal"><code>rawequal (v1, v2)</code></a></h3>
- Checks whether <code>v1</code> is equal to <code>v2</code>,
- without invoking any metamethod.
- Returns a boolean.
- <p>
- <hr><h3><a name="pdf-rawget"><code>rawget (table, index)</code></a></h3>
- Gets the real value of <code>table[index]</code>,
- without invoking any metamethod.
- <code>table</code> must be a table;
- <code>index</code> may be any value.
- <p>
- <hr><h3><a name="pdf-rawlen"><code>rawlen (v)</code></a></h3>
- Returns the length of the object <code>v</code>,
- which must be a table or a string,
- without invoking any metamethod.
- Returns an integer number.
- <p>
- <hr><h3><a name="pdf-rawset"><code>rawset (table, index, value)</code></a></h3>
- Sets the real value of <code>table[index]</code> to <code>value</code>,
- without invoking any metamethod.
- <code>table</code> must be a table,
- <code>index</code> any value different from <b>nil</b> and NaN,
- and <code>value</code> any Lua value.
- <p>
- This function returns <code>table</code>.
- <p>
- <hr><h3><a name="pdf-select"><code>select (index, ···)</code></a></h3>
- <p>
- If <code>index</code> is a number,
- returns all arguments after argument number <code>index</code>;
- a negative number indexes from the end (-1 is the last argument).
- Otherwise, <code>index</code> must be the string <code>"#"</code>,
- and <code>select</code> returns the total number of extra arguments it received.
- <p>
- <hr><h3><a name="pdf-setmetatable"><code>setmetatable (table, metatable)</code></a></h3>
- <p>
- Sets the metatable for the given table.
- (You cannot change the metatable of other types from Lua, only from C.)
- If <code>metatable</code> is <b>nil</b>,
- removes the metatable of the given table.
- If the original metatable has a <code>"__metatable"</code> field,
- raises an error.
- <p>
- This function returns <code>table</code>.
- <p>
- <hr><h3><a name="pdf-tonumber"><code>tonumber (e [, base])</code></a></h3>
- <p>
- When called with no <code>base</code>,
- <code>tonumber</code> tries to convert its argument to a number.
- If the argument is already a number or
- a string convertible to a number (see <a href="#3.4.2">§3.4.2</a>),
- then <code>tonumber</code> returns this number;
- otherwise, it returns <b>nil</b>.
- <p>
- When called with <code>base</code>,
- then <code>e</code> should be a string to be interpreted as
- an integer numeral in that base.
- The base may be any integer between 2 and 36, inclusive.
- In bases above 10, the letter '<code>A</code>' (in either upper or lower case)
- represents 10, '<code>B</code>' represents 11, and so forth,
- with '<code>Z</code>' representing 35.
- If the string <code>e</code> is not a valid numeral in the given base,
- the function returns <b>nil</b>.
- <p>
- <hr><h3><a name="pdf-tostring"><code>tostring (v)</code></a></h3>
- Receives a value of any type and
- converts it to a string in a reasonable format.
- (For complete control of how numbers are converted,
- use <a href="#pdf-string.format"><code>string.format</code></a>.)
- <p>
- If the metatable of <code>v</code> has a <code>"__tostring"</code> field,
- then <code>tostring</code> calls the corresponding value
- with <code>v</code> as argument,
- and uses the result of the call as its result.
- <p>
- <hr><h3><a name="pdf-type"><code>type (v)</code></a></h3>
- Returns the type of its only argument, coded as a string.
- The possible results of this function are
- "<code>nil</code>" (a string, not the value <b>nil</b>),
- "<code>number</code>",
- "<code>string</code>",
- "<code>boolean</code>",
- "<code>table</code>",
- "<code>function</code>",
- "<code>thread</code>",
- and "<code>userdata</code>".
- <p>
- <hr><h3><a name="pdf-_VERSION"><code>_VERSION</code></a></h3>
- A global variable (not a function) that
- holds a string containing the current interpreter version.
- The current contents of this variable is "<code>Lua 5.2</code>".
- <p>
- <hr><h3><a name="pdf-xpcall"><code>xpcall (f, msgh [, arg1, ···])</code></a></h3>
- <p>
- This function is similar to <a href="#pdf-pcall"><code>pcall</code></a>,
- except that it sets a new message handler <code>msgh</code>.
- <h2>6.2 – <a name="6.2">Coroutine Manipulation</a></h2>
- <p>
- The operations related to coroutines comprise a sub-library of
- the basic library and come inside the table <a name="pdf-coroutine"><code>coroutine</code></a>.
- See <a href="#2.6">§2.6</a> for a general description of coroutines.
- <p>
- <hr><h3><a name="pdf-coroutine.create"><code>coroutine.create (f)</code></a></h3>
- <p>
- Creates a new coroutine, with body <code>f</code>.
- <code>f</code> must be a Lua function.
- Returns this new coroutine,
- an object with type <code>"thread"</code>.
- <p>
- <hr><h3><a name="pdf-coroutine.resume"><code>coroutine.resume (co [, val1, ···])</code></a></h3>
- <p>
- Starts or continues the execution of coroutine <code>co</code>.
- The first time you resume a coroutine,
- it starts running its body.
- The values <code>val1</code>, ... are passed
- as the arguments to the body function.
- If the coroutine has yielded,
- <code>resume</code> restarts it;
- the values <code>val1</code>, ... are passed
- as the results from the yield.
- <p>
- If the coroutine runs without any errors,
- <code>resume</code> returns <b>true</b> plus any values passed to <code>yield</code>
- (if the coroutine yields) or any values returned by the body function
- (if the coroutine terminates).
- If there is any error,
- <code>resume</code> returns <b>false</b> plus the error message.
- <p>
- <hr><h3><a name="pdf-coroutine.running"><code>coroutine.running ()</code></a></h3>
- <p>
- Returns the running coroutine plus a boolean,
- true when the running coroutine is the main one.
- <p>
- <hr><h3><a name="pdf-coroutine.status"><code>coroutine.status (co)</code></a></h3>
- <p>
- Returns the status of coroutine <code>co</code>, as a string:
- <code>"running"</code>,
- if the coroutine is running (that is, it called <code>status</code>);
- <code>"suspended"</code>, if the coroutine is suspended in a call to <code>yield</code>,
- or if it has not started running yet;
- <code>"normal"</code> if the coroutine is active but not running
- (that is, it has resumed another coroutine);
- and <code>"dead"</code> if the coroutine has finished its body function,
- or if it has stopped with an error.
- <p>
- <hr><h3><a name="pdf-coroutine.wrap"><code>coroutine.wrap (f)</code></a></h3>
- <p>
- Creates a new coroutine, with body <code>f</code>.
- <code>f</code> must be a Lua function.
- Returns a function that resumes the coroutine each time it is called.
- Any arguments passed to the function behave as the
- extra arguments to <code>resume</code>.
- Returns the same values returned by <code>resume</code>,
- except the first boolean.
- In case of error, propagates the error.
- <p>
- <hr><h3><a name="pdf-coroutine.yield"><code>coroutine.yield (···)</code></a></h3>
- <p>
- Suspends the execution of the calling coroutine.
- Any arguments to <code>yield</code> are passed as extra results to <code>resume</code>.
- <h2>6.3 – <a name="6.3">Modules</a></h2>
- <p>
- The package library provides basic
- facilities for loading modules in Lua.
- It exports one function directly in the global environment:
- <a href="#pdf-require"><code>require</code></a>.
- Everything else is exported in a table <a name="pdf-package"><code>package</code></a>.
- <p>
- <hr><h3><a name="pdf-require"><code>require (modname)</code></a></h3>
- <p>
- Loads the given module.
- The function starts by looking into the <a href="#pdf-package.loaded"><code>package.loaded</code></a> table
- to determine whether <code>modname</code> is already loaded.
- If it is, then <code>require</code> returns the value stored
- at <code>package.loaded[modname]</code>.
- Otherwise, it tries to find a <em>loader</em> for the module.
- <p>
- To find a loader,
- <code>require</code> is guided by the <a href="#pdf-package.searchers"><code>package.searchers</code></a> sequence.
- By changing this sequence,
- we can change how <code>require</code> looks for a module.
- The following explanation is based on the default configuration
- for <a href="#pdf-package.searchers"><code>package.searchers</code></a>.
- <p>
- First <code>require</code> queries <code>package.preload[modname]</code>.
- If it has a value,
- this value (which should be a function) is the loader.
- Otherwise <code>require</code> searches for a Lua loader using the
- path stored in <a href="#pdf-package.path"><code>package.path</code></a>.
- If that also fails, it searches for a C loader using the
- path stored in <a href="#pdf-package.cpath"><code>package.cpath</code></a>.
- If that also fails,
- it tries an <em>all-in-one</em> loader (see <a href="#pdf-package.searchers"><code>package.searchers</code></a>).
- <p>
- Once a loader is found,
- <code>require</code> calls the loader with two arguments:
- <code>modname</code> and an extra value dependent on how it got the loader.
- (If the loader came from a file,
- this extra value is the file name.)
- If the loader returns any non-nil value,
- <code>require</code> assigns the returned value to <code>package.loaded[modname]</code>.
- If the loader does not return a non-nil value and
- has not assigned any value to <code>package.loaded[modname]</code>,
- then <code>require</code> assigns <b>true</b> to this entry.
- In any case, <code>require</code> returns the
- final value of <code>package.loaded[modname]</code>.
- <p>
- If there is any error loading or running the module,
- or if it cannot find any loader for the module,
- then <code>require</code> raises an error.
- <p>
- <hr><h3><a name="pdf-package.config"><code>package.config</code></a></h3>
- <p>
- A string describing some compile-time configurations for packages.
- This string is a sequence of lines:
- <ul>
- <li>The first line is the directory separator string.
- Default is '<code>\</code>' for Windows and '<code>/</code>' for all other systems.</li>
- <li>The second line is the character that separates templates in a path.
- Default is '<code>;</code>'.</li>
- <li>The third line is the string that marks the
- substitution points in a template.
- Default is '<code>?</code>'.</li>
- <li>The fourth line is a string that, in a path in Windows,
- is replaced by the executable's directory.
- Default is '<code>!</code>'.</li>
- <li>The fifth line is a mark to ignore all text before it
- when building the <code>luaopen_</code> function name.
- Default is '<code>-</code>'.</li>
- </ul>
- <p>
- <hr><h3><a name="pdf-package.cpath"><code>package.cpath</code></a></h3>
- <p>
- The path used by <a href="#pdf-require"><code>require</code></a> to search for a C loader.
- <p>
- Lua initializes the C path <a href="#pdf-package.cpath"><code>package.cpath</code></a> in the same way
- it initializes the Lua path <a href="#pdf-package.path"><code>package.path</code></a>,
- using the environment variable <a name="pdf-LUA_CPATH_5_2"><code>LUA_CPATH_5_2</code></a>
- or the environment variable <a name="pdf-LUA_CPATH"><code>LUA_CPATH</code></a>
- or a default path defined in <code>luaconf.h</code>.
- <p>
- <hr><h3><a name="pdf-package.loaded"><code>package.loaded</code></a></h3>
- <p>
- A table used by <a href="#pdf-require"><code>require</code></a> to control which
- modules are already loaded.
- When you require a module <code>modname</code> and
- <code>package.loaded[modname]</code> is not false,
- <a href="#pdf-require"><code>require</code></a> simply returns the value stored there.
- <p>
- This variable is only a reference to the real table;
- assignments to this variable do not change the
- table used by <a href="#pdf-require"><code>require</code></a>.
- <p>
- <hr><h3><a name="pdf-package.loadlib"><code>package.loadlib (libname, funcname)</code></a></h3>
- <p>
- Dynamically links the host program with the C library <code>libname</code>.
- <p>
- If <code>funcname</code> is "<code>*</code>",
- then it only links with the library,
- making the symbols exported by the library
- available to other dynamically linked libraries.
- Otherwise,
- it looks for a function <code>funcname</code> inside the library
- and returns this function as a C function.
- So, <code>funcname</code> must follow the <a href="#lua_CFunction"><code>lua_CFunction</code></a> prototype
- (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
- <p>
- This is a low-level function.
- It completely bypasses the package and module system.
- Unlike <a href="#pdf-require"><code>require</code></a>,
- it does not perform any path searching and
- does not automatically adds extensions.
- <code>libname</code> must be the complete file name of the C library,
- including if necessary a path and an extension.
- <code>funcname</code> must be the exact name exported by the C library
- (which may depend on the C compiler and linker used).
- <p>
- This function is not supported by Standard C.
- As such, it is only available on some platforms
- (Windows, Linux, Mac OS X, Solaris, BSD,
- plus other Unix systems that support the <code>dlfcn</code> standard).
- <p>
- <hr><h3><a name="pdf-package.path"><code>package.path</code></a></h3>
- <p>
- The path used by <a href="#pdf-require"><code>require</code></a> to search for a Lua loader.
- <p>
- At start-up, Lua initializes this variable with
- the value of the environment variable <a name="pdf-LUA_PATH_5_2"><code>LUA_PATH_5_2</code></a> or
- the environment variable <a name="pdf-LUA_PATH"><code>LUA_PATH</code></a> or
- with a default path defined in <code>luaconf.h</code>,
- if those environment variables are not defined.
- Any "<code>;;</code>" in the value of the environment variable
- is replaced by the default path.
- <p>
- <hr><h3><a name="pdf-package.preload"><code>package.preload</code></a></h3>
- <p>
- A table to store loaders for specific modules
- (see <a href="#pdf-require"><code>require</code></a>).
- <p>
- This variable is only a reference to the real table;
- assignments to this variable do not change the
- table used by <a href="#pdf-require"><code>require</code></a>.
- <p>
- <hr><h3><a name="pdf-package.searchers"><code>package.searchers</code></a></h3>
- <p>
- A table used by <a href="#pdf-require"><code>require</code></a> to control how to load modules.
- <p>
- Each entry in this table is a <em>searcher function</em>.
- When looking for a module,
- <a href="#pdf-require"><code>require</code></a> calls each of these searchers in ascending order,
- with the module name (the argument given to <a href="#pdf-require"><code>require</code></a>) as its
- sole parameter.
- The function can return another function (the module <em>loader</em>)
- plus an extra value that will be passed to that loader,
- or a string explaining why it did not find that module
- (or <b>nil</b> if it has nothing to say).
- <p>
- Lua initializes this table with four searcher functions.
- <p>
- The first searcher simply looks for a loader in the
- <a href="#pdf-package.preload"><code>package.preload</code></a> table.
- <p>
- The second searcher looks for a loader as a Lua library,
- using the path stored at <a href="#pdf-package.path"><code>package.path</code></a>.
- The search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>.
- <p>
- The third searcher looks for a loader as a C library,
- using the path given by the variable <a href="#pdf-package.cpath"><code>package.cpath</code></a>.
- Again,
- the search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>.
- For instance,
- if the C path is the string
- <pre>
- "./?.so;./?.dll;/usr/local/?/init.so"
- </pre><p>
- the searcher for module <code>foo</code>
- will try to open the files <code>./foo.so</code>, <code>./foo.dll</code>,
- and <code>/usr/local/foo/init.so</code>, in that order.
- Once it finds a C library,
- this searcher first uses a dynamic link facility to link the
- application with the library.
- Then it tries to find a C function inside the library to
- be used as the loader.
- The name of this C function is the string "<code>luaopen_</code>"
- concatenated with a copy of the module name where each dot
- is replaced by an underscore.
- Moreover, if the module name has a hyphen,
- its prefix up to (and including) the first hyphen is removed.
- For instance, if the module name is <code>a.v1-b.c</code>,
- the function name will be <code>luaopen_b_c</code>.
- <p>
- The fourth searcher tries an <em>all-in-one loader</em>.
- It searches the C path for a library for
- the root name of the given module.
- For instance, when requiring <code>a.b.c</code>,
- it will search for a C library for <code>a</code>.
- If found, it looks into it for an open function for
- the submodule;
- in our example, that would be <code>luaopen_a_b_c</code>.
- With this facility, a package can pack several C submodules
- into one single library,
- with each submodule keeping its original open function.
- <p>
- All searchers except the first one (preload) return as the extra value
- the file name where the module was found,
- as returned by <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>.
- The first searcher returns no extra value.
- <p>
- <hr><h3><a name="pdf-package.searchpath"><code>package.searchpath (name, path [, sep [, rep]])</code></a></h3>
- <p>
- Searches for the given <code>name</code> in the given <code>path</code>.
- <p>
- A path is a string containing a sequence of
- <em>templates</em> separated by semicolons.
- For each template,
- the function replaces each interrogation mark (if any)
- in the template with a copy of <code>name</code>
- wherein all occurrences of <code>sep</code>
- (a dot, by default)
- were replaced by <code>rep</code>
- (the system's directory separator, by default),
- and then tries to open the resulting file name.
- <p>
- For instance, if the path is the string
- <pre>
- "./?.lua;./?.lc;/usr/local/?/init.lua"
- </pre><p>
- the search for the name <code>foo.a</code>
- will try to open the files
- <code>./foo/a.lua</code>, <code>./foo/a.lc</code>, and
- <code>/usr/local/foo/a/init.lua</code>, in that order.
- <p>
- Returns the resulting name of the first file that it can
- open in read mode (after closing the file),
- or <b>nil</b> plus an error message if none succeeds.
- (This error message lists all file names it tried to open.)
- <h2>6.4 – <a name="6.4">String Manipulation</a></h2>
- <p>
- This library provides generic functions for string manipulation,
- such as finding and extracting substrings, and pattern matching.
- When indexing a string in Lua, the first character is at position 1
- (not at 0, as in C).
- Indices are allowed to be negative and are interpreted as indexing backwards,
- from the end of the string.
- Thus, the last character is at position -1, and so on.
- <p>
- The string library provides all its functions inside the table
- <a name="pdf-string"><code>string</code></a>.
- It also sets a metatable for strings
- where the <code>__index</code> field points to the <code>string</code> table.
- Therefore, you can use the string functions in object-oriented style.
- For instance, <code>string.byte(s,i)</code>
- can be written as <code>s:byte(i)</code>.
- <p>
- The string library assumes one-byte character encodings.
- <p>
- <hr><h3><a name="pdf-string.byte"><code>string.byte (s [, i [, j]])</code></a></h3>
- Returns the internal numerical codes of the characters <code>s[i]</code>,
- <code>s[i+1]</code>, ..., <code>s[j]</code>.
- The default value for <code>i</code> is 1;
- the default value for <code>j</code> is <code>i</code>.
- These indices are corrected
- following the same rules of function <a href="#pdf-string.sub"><code>string.sub</code></a>.
- <p>
- Numerical codes are not necessarily portable across platforms.
- <p>
- <hr><h3><a name="pdf-string.char"><code>string.char (···)</code></a></h3>
- Receives zero or more integers.
- Returns a string with length equal to the number of arguments,
- in which each character has the internal numerical code equal
- to its corresponding argument.
- <p>
- Numerical codes are not necessarily portable across platforms.
- <p>
- <hr><h3><a name="pdf-string.dump"><code>string.dump (function)</code></a></h3>
- <p>
- Returns a string containing a binary representation of the given function,
- so that a later <a href="#pdf-load"><code>load</code></a> on this string returns
- a copy of the function (but with new upvalues).
- <p>
- <hr><h3><a name="pdf-string.find"><code>string.find (s, pattern [, init [, plain]])</code></a></h3>
- <p>
- Looks for the first match of
- <code>pattern</code> in the string <code>s</code>.
- If it finds a match, then <code>find</code> returns the indices of <code>s</code>
- where this occurrence starts and ends;
- otherwise, it returns <b>nil</b>.
- A third, optional numerical argument <code>init</code> specifies
- where to start the search;
- its default value is 1 and can be negative.
- A value of <b>true</b> as a fourth, optional argument <code>plain</code>
- turns off the pattern matching facilities,
- so the function does a plain "find substring" operation,
- with no characters in <code>pattern</code> being considered magic.
- Note that if <code>plain</code> is given, then <code>init</code> must be given as well.
- <p>
- If the pattern has captures,
- then in a successful match
- the captured values are also returned,
- after the two indices.
- <p>
- <hr><h3><a name="pdf-string.format"><code>string.format (formatstring, ···)</code></a></h3>
- <p>
- Returns a formatted version of its variable number of arguments
- following the description given in its first argument (which must be a string).
- The format string follows the same rules as the ISO C function <code>sprintf</code>.
- The only differences are that the options/modifiers
- <code>*</code>, <code>h</code>, <code>L</code>, <code>l</code>, <code>n</code>,
- and <code>p</code> are not supported
- and that there is an extra option, <code>q</code>.
- The <code>q</code> option formats a string between double quotes,
- using escape sequences when necessary to ensure that
- it can safely be read back by the Lua interpreter.
- For instance, the call
- <pre>
- string.format('%q', 'a string with "quotes" and \n new line')
- </pre><p>
- may produce the string:
- <pre>
- "a string with \"quotes\" and \
- new line"
- </pre>
- <p>
- Options
- <code>A</code> and <code>a</code> (when available),
- <code>E</code>, <code>e</code>, <code>f</code>,
- <code>G</code>, and <code>g</code> all expect a number as argument.
- Options <code>c</code>, <code>d</code>,
- <code>i</code>, <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code>
- also expect a number,
- but the range of that number may be limited by
- the underlying C implementation.
- For options <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code>,
- the number cannot be negative.
- Option <code>q</code> expects a string;
- option <code>s</code> expects a string without embedded zeros.
- If the argument to option <code>s</code> is not a string,
- it is converted to one following the same rules of <a href="#pdf-tostring"><code>tostring</code></a>.
- <p>
- <hr><h3><a name="pdf-string.gmatch"><code>string.gmatch (s, pattern)</code></a></h3>
- Returns an iterator function that,
- each time it is called,
- returns the next captures from <code>pattern</code> over the string <code>s</code>.
- If <code>pattern</code> specifies no captures,
- then the whole match is produced in each call.
- <p>
- As an example, the following loop
- will iterate over all the words from string <code>s</code>,
- printing one per line:
- <pre>
- s = "hello world from Lua"
- for w in string.gmatch(s, "%a+") do
- print(w)
- end
- </pre><p>
- The next example collects all pairs <code>key=value</code> from the
- given string into a table:
- <pre>
- t = {}
- s = "from=world, to=Lua"
- for k, v in string.gmatch(s, "(%w+)=(%w+)") do
- t[k] = v
- end
- </pre>
- <p>
- For this function, a caret '<code>^</code>' at the start of a pattern does not
- work as an anchor, as this would prevent the iteration.
- <p>
- <hr><h3><a name="pdf-string.gsub"><code>string.gsub (s, pattern, repl [, n])</code></a></h3>
- Returns a copy of <code>s</code>
- in which all (or the first <code>n</code>, if given)
- occurrences of the <code>pattern</code> have been
- replaced by a replacement string specified by <code>repl</code>,
- which can be a string, a table, or a function.
- <code>gsub</code> also returns, as its second value,
- the total number of matches that occurred.
- The name <code>gsub</code> comes from <em>Global SUBstitution</em>.
- <p>
- If <code>repl</code> is a string, then its value is used for replacement.
- The character <code>%</code> works as an escape character:
- any sequence in <code>repl</code> of the form <code>%<em>d</em></code>,
- with <em>d</em> between 1 and 9,
- stands for the value of the <em>d</em>-th captured substring.
- The sequence <code>%0</code> stands for the whole match.
- The sequence <code>%%</code> stands for a single <code>%</code>.
- <p>
- If <code>repl</code> is a table, then the table is queried for every match,
- using the first capture as the key.
- <p>
- If <code>repl</code> is a function, then this function is called every time a
- match occurs, with all captured substrings passed as arguments,
- in order.
- <p>
- In any case,
- if the pattern specifies no captures,
- then it behaves as if the whole pattern was inside a capture.
- <p>
- If the value returned by the table query or by the function call
- is a string or a number,
- then it is used as the replacement string;
- otherwise, if it is <b>false</b> or <b>nil</b>,
- then there is no replacement
- (that is, the original match is kept in the string).
- <p>
- Here are some examples:
- <pre>
- x = string.gsub("hello world", "(%w+)", "%1 %1")
- --> x="hello hello world world"
-
- x = string.gsub("hello world", "%w+", "%0 %0", 1)
- --> x="hello hello world"
-
- x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1")
- --> x="world hello Lua from"
-
- x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv)
- --> x="home = /home/roberto, user = roberto"
-
- x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s)
- return load(s)()
- end)
- --> x="4+5 = 9"
-
- local t = {name="lua", version="5.2"}
- x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t)
- --> x="lua-5.2.tar.gz"
- </pre>
- <p>
- <hr><h3><a name="pdf-string.len"><code>string.len (s)</code></a></h3>
- Receives a string and returns its length.
- The empty string <code>""</code> has length 0.
- Embedded zeros are counted,
- so <code>"a\000bc\000"</code> has length 5.
- <p>
- <hr><h3><a name="pdf-string.lower"><code>string.lower (s)</code></a></h3>
- Receives a string and returns a copy of this string with all
- uppercase letters changed to lowercase.
- All other characters are left unchanged.
- The definition of what an uppercase letter is depends on the current locale.
- <p>
- <hr><h3><a name="pdf-string.match"><code>string.match (s, pattern [, init])</code></a></h3>
- Looks for the first <em>match</em> of
- <code>pattern</code> in the string <code>s</code>.
- If it finds one, then <code>match</code> returns
- the captures from the pattern;
- otherwise it returns <b>nil</b>.
- If <code>pattern</code> specifies no captures,
- then the whole match is returned.
- A third, optional numerical argument <code>init</code> specifies
- where to start the search;
- its default value is 1 and can be negative.
- <p>
- <hr><h3><a name="pdf-string.rep"><code>string.rep (s, n [, sep])</code></a></h3>
- Returns a string that is the concatenation of <code>n</code> copies of
- the string <code>s</code> separated by the string <code>sep</code>.
- The default value for <code>sep</code> is the empty string
- (that is, no separator).
- <p>
- <hr><h3><a name="pdf-string.reverse"><code>string.reverse (s)</code></a></h3>
- Returns a string that is the string <code>s</code> reversed.
- <p>
- <hr><h3><a name="pdf-string.sub"><code>string.sub (s, i [, j])</code></a></h3>
- Returns the substring of <code>s</code> that
- starts at <code>i</code> and continues until <code>j</code>;
- <code>i</code> and <code>j</code> can be negative.
- If <code>j</code> is absent, then it is assumed to be equal to -1
- (which is the same as the string length).
- In particular,
- the call <code>string.sub(s,1,j)</code> returns a prefix of <code>s</code>
- with length <code>j</code>,
- and <code>string.sub(s, -i)</code> returns a suffix of <code>s</code>
- with length <code>i</code>.
- <p>
- If, after the translation of negative indices,
- <code>i</code> is less than 1,
- it is corrected to 1.
- If <code>j</code> is greater than the string length,
- it is corrected to that length.
- If, after these corrections,
- <code>i</code> is greater than <code>j</code>,
- the function returns the empty string.
- <p>
- <hr><h3><a name="pdf-string.upper"><code>string.upper (s)</code></a></h3>
- Receives a string and returns a copy of this string with all
- lowercase letters changed to uppercase.
- All other characters are left unchanged.
- The definition of what a lowercase letter is depends on the current locale.
- <h3>6.4.1 – <a name="6.4.1">Patterns</a></h3>
- <h4>Character Class:</h4><p>
- A <em>character class</em> is used to represent a set of characters.
- The following combinations are allowed in describing a character class:
- <ul>
- <li><b><em>x</em>: </b>
- (where <em>x</em> is not one of the <em>magic characters</em>
- <code>^$()%.[]*+-?</code>)
- represents the character <em>x</em> itself.
- </li>
- <li><b><code>.</code>: </b> (a dot) represents all characters.</li>
- <li><b><code>%a</code>: </b> represents all letters.</li>
- <li><b><code>%c</code>: </b> represents all control characters.</li>
- <li><b><code>%d</code>: </b> represents all digits.</li>
- <li><b><code>%g</code>: </b> represents all printable characters except space.</li>
- <li><b><code>%l</code>: </b> represents all lowercase letters.</li>
- <li><b><code>%p</code>: </b> represents all punctuation characters.</li>
- <li><b><code>%s</code>: </b> represents all space characters.</li>
- <li><b><code>%u</code>: </b> represents all uppercase letters.</li>
- <li><b><code>%w</code>: </b> represents all alphanumeric characters.</li>
- <li><b><code>%x</code>: </b> represents all hexadecimal digits.</li>
- <li><b><code>%<em>x</em></code>: </b> (where <em>x</em> is any non-alphanumeric character)
- represents the character <em>x</em>.
- This is the standard way to escape the magic characters.
- Any punctuation character (even the non magic)
- can be preceded by a '<code>%</code>'
- when used to represent itself in a pattern.
- </li>
- <li><b><code>[<em>set</em>]</code>: </b>
- represents the class which is the union of all
- characters in <em>set</em>.
- A range of characters can be specified by
- separating the end characters of the range,
- in ascending order, with a '<code>-</code>',
- All classes <code>%</code><em>x</em> described above can also be used as
- components in <em>set</em>.
- All other characters in <em>set</em> represent themselves.
- For example, <code>[%w_]</code> (or <code>[_%w]</code>)
- represents all alphanumeric characters plus the underscore,
- <code>[0-7]</code> represents the octal digits,
- and <code>[0-7%l%-]</code> represents the octal digits plus
- the lowercase letters plus the '<code>-</code>' character.
- <p>
- The interaction between ranges and classes is not defined.
- Therefore, patterns like <code>[%a-z]</code> or <code>[a-%%]</code>
- have no meaning.
- </li>
- <li><b><code>[^<em>set</em>]</code>: </b>
- represents the complement of <em>set</em>,
- where <em>set</em> is interpreted as above.
- </li>
- </ul><p>
- For all classes represented by single letters (<code>%a</code>, <code>%c</code>, etc.),
- the corresponding uppercase letter represents the complement of the class.
- For instance, <code>%S</code> represents all non-space characters.
- <p>
- The definitions of letter, space, and other character groups
- depend on the current locale.
- In particular, the class <code>[a-z]</code> may not be equivalent to <code>%l</code>.
- <h4>Pattern Item:</h4><p>
- A <em>pattern item</em> can be
- <ul>
- <li>
- a single character class,
- which matches any single character in the class;
- </li>
- <li>
- a single character class followed by '<code>*</code>',
- which matches 0 or more repetitions of characters in the class.
- These repetition items will always match the longest possible sequence;
- </li>
- <li>
- a single character class followed by '<code>+</code>',
- which matches 1 or more repetitions of characters in the class.
- These repetition items will always match the longest possible sequence;
- </li>
- <li>
- a single character class followed by '<code>-</code>',
- which also matches 0 or more repetitions of characters in the class.
- Unlike '<code>*</code>',
- these repetition items will always match the shortest possible sequence;
- </li>
- <li>
- a single character class followed by '<code>?</code>',
- which matches 0 or 1 occurrence of a character in the class;
- </li>
- <li>
- <code>%<em>n</em></code>, for <em>n</em> between 1 and 9;
- such item matches a substring equal to the <em>n</em>-th captured string
- (see below);
- </li>
- <li>
- <code>%b<em>xy</em></code>, where <em>x</em> and <em>y</em> are two distinct characters;
- such item matches strings that start with <em>x</em>, end with <em>y</em>,
- and where the <em>x</em> and <em>y</em> are <em>balanced</em>.
- This means that, if one reads the string from left to right,
- counting <em>+1</em> for an <em>x</em> and <em>-1</em> for a <em>y</em>,
- the ending <em>y</em> is the first <em>y</em> where the count reaches 0.
- For instance, the item <code>%b()</code> matches expressions with
- balanced parentheses.
- </li>
- <li>
- <code>%f[<em>set</em>]</code>, a <em>frontier pattern</em>;
- such item matches an empty string at any position such that
- the next character belongs to <em>set</em>
- and the previous character does not belong to <em>set</em>.
- The set <em>set</em> is interpreted as previously described.
- The beginning and the end of the subject are handled as if
- they were the character '<code>\0</code>'.
- </li>
- </ul>
- <h4>Pattern:</h4><p>
- A <em>pattern</em> is a sequence of pattern items.
- A caret '<code>^</code>' at the beginning of a pattern anchors the match at the
- beginning of the subject string.
- A '<code>$</code>' at the end of a pattern anchors the match at the
- end of the subject string.
- At other positions,
- '<code>^</code>' and '<code>$</code>' have no special meaning and represent themselves.
- <h4>Captures:</h4><p>
- A pattern can contain sub-patterns enclosed in parentheses;
- they describe <em>captures</em>.
- When a match succeeds, the substrings of the subject string
- that match captures are stored (<em>captured</em>) for future use.
- Captures are numbered according to their left parentheses.
- For instance, in the pattern <code>"(a*(.)%w(%s*))"</code>,
- the part of the string matching <code>"a*(.)%w(%s*)"</code> is
- stored as the first capture (and therefore has number 1);
- the character matching "<code>.</code>" is captured with number 2,
- and the part matching "<code>%s*</code>" has number 3.
- <p>
- As a special case, the empty capture <code>()</code> captures
- the current string position (a number).
- For instance, if we apply the pattern <code>"()aa()"</code> on the
- string <code>"flaaap"</code>, there will be two captures: 3 and 5.
- <h2>6.5 – <a name="6.5">Table Manipulation</a></h2>
- <p>
- This library provides generic functions for table manipulation.
- It provides all its functions inside the table <a name="pdf-table"><code>table</code></a>.
- <p>
- Remember that, whenever an operation needs the length of a table,
- the table should be a proper sequence
- or have a <code>__len</code> metamethod (see <a href="#3.4.6">§3.4.6</a>).
- All functions ignore non-numeric keys
- in tables given as arguments.
- <p>
- For performance reasons,
- all table accesses (get/set) performed by these functions are raw.
- <p>
- <hr><h3><a name="pdf-table.concat"><code>table.concat (list [, sep [, i [, j]]])</code></a></h3>
- <p>
- Given a list where all elements are strings or numbers,
- returns the string <code>list[i]..sep..list[i+1] ··· sep..list[j]</code>.
- The default value for <code>sep</code> is the empty string,
- the default for <code>i</code> is 1,
- and the default for <code>j</code> is <code>#list</code>.
- If <code>i</code> is greater than <code>j</code>, returns the empty string.
- <p>
- <hr><h3><a name="pdf-table.insert"><code>table.insert (list, [pos,] value)</code></a></h3>
- <p>
- Inserts element <code>value</code> at position <code>pos</code> in <code>list</code>,
- shifting up the elements
- <code>list[pos], list[pos+1], ···, list[#list]</code>.
- The default value for <code>pos</code> is <code>#list+1</code>,
- so that a call <code>table.insert(t,x)</code> inserts <code>x</code> at the end
- of list <code>t</code>.
- <p>
- <hr><h3><a name="pdf-table.pack"><code>table.pack (···)</code></a></h3>
- <p>
- Returns a new table with all parameters stored into keys 1, 2, etc.
- and with a field "<code>n</code>" with the total number of parameters.
- Note that the resulting table may not be a sequence.
- <p>
- <hr><h3><a name="pdf-table.remove"><code>table.remove (list [, pos])</code></a></h3>
- <p>
- Removes from <code>list</code> the element at position <code>pos</code>,
- returning the value of the removed element.
- When <code>pos</code> is an integer between 1 and <code>#list</code>,
- it shifts down the elements
- <code>list[pos+1], list[pos+2], ···, list[#list]</code>
- and erases element <code>list[#list]</code>;
- The index <code>pos</code> can also be 0 when <code>#list</code> is 0,
- or <code>#list + 1</code>;
- in those cases, the function erases the element <code>list[pos]</code>.
- <p>
- The default value for <code>pos</code> is <code>#list</code>,
- so that a call <code>table.remove(t)</code> removes the last element
- of list <code>t</code>.
- <p>
- <hr><h3><a name="pdf-table.sort"><code>table.sort (list [, comp])</code></a></h3>
- <p>
- Sorts list elements in a given order, <em>in-place</em>,
- from <code>list[1]</code> to <code>list[#list]</code>.
- If <code>comp</code> is given,
- then it must be a function that receives two list elements
- and returns true when the first element must come
- before the second in the final order
- (so that <code>not comp(list[i+1],list[i])</code> will be true after the sort).
- If <code>comp</code> is not given,
- then the standard Lua operator <code><</code> is used instead.
- <p>
- The sort algorithm is not stable;
- that is, elements considered equal by the given order
- may have their relative positions changed by the sort.
- <p>
- <hr><h3><a name="pdf-table.unpack"><code>table.unpack (list [, i [, j]])</code></a></h3>
- <p>
- Returns the elements from the given table.
- This function is equivalent to
- <pre>
- return list[i], list[i+1], ···, list[j]
- </pre><p>
- By default, <code>i</code> is 1 and <code>j</code> is <code>#list</code>.
- <h2>6.6 – <a name="6.6">Mathematical Functions</a></h2>
- <p>
- This library is an interface to the standard C math library.
- It provides all its functions inside the table <a name="pdf-math"><code>math</code></a>.
- <p>
- <hr><h3><a name="pdf-math.abs"><code>math.abs (x)</code></a></h3>
- <p>
- Returns the absolute value of <code>x</code>.
- <p>
- <hr><h3><a name="pdf-math.acos"><code>math.acos (x)</code></a></h3>
- <p>
- Returns the arc cosine of <code>x</code> (in radians).
- <p>
- <hr><h3><a name="pdf-math.asin"><code>math.asin (x)</code></a></h3>
- <p>
- Returns the arc sine of <code>x</code> (in radians).
- <p>
- <hr><h3><a name="pdf-math.atan"><code>math.atan (x)</code></a></h3>
- <p>
- Returns the arc tangent of <code>x</code> (in radians).
- <p>
- <hr><h3><a name="pdf-math.atan2"><code>math.atan2 (y, x)</code></a></h3>
- <p>
- Returns the arc tangent of <code>y/x</code> (in radians),
- but uses the signs of both parameters to find the
- quadrant of the result.
- (It also handles correctly the case of <code>x</code> being zero.)
- <p>
- <hr><h3><a name="pdf-math.ceil"><code>math.ceil (x)</code></a></h3>
- <p>
- Returns the smallest integer larger than or equal to <code>x</code>.
- <p>
- <hr><h3><a name="pdf-math.cos"><code>math.cos (x)</code></a></h3>
- <p>
- Returns the cosine of <code>x</code> (assumed to be in radians).
- <p>
- <hr><h3><a name="pdf-math.cosh"><code>math.cosh (x)</code></a></h3>
- <p>
- Returns the hyperbolic cosine of <code>x</code>.
- <p>
- <hr><h3><a name="pdf-math.deg"><code>math.deg (x)</code></a></h3>
- <p>
- Returns the angle <code>x</code> (given in radians) in degrees.
- <p>
- <hr><h3><a name="pdf-math.exp"><code>math.exp (x)</code></a></h3>
- <p>
- Returns the value <em>e<sup>x</sup></em>.
- <p>
- <hr><h3><a name="pdf-math.floor"><code>math.floor (x)</code></a></h3>
- <p>
- Returns the largest integer smaller than or equal to <code>x</code>.
- <p>
- <hr><h3><a name="pdf-math.fmod"><code>math.fmod (x, y)</code></a></h3>
- <p>
- Returns the remainder of the division of <code>x</code> by <code>y</code>
- that rounds the quotient towards zero.
- <p>
- <hr><h3><a name="pdf-math.frexp"><code>math.frexp (x)</code></a></h3>
- <p>
- Returns <code>m</code> and <code>e</code> such that <em>x = m2<sup>e</sup></em>,
- <code>e</code> is an integer and the absolute value of <code>m</code> is
- in the range <em>[0.5, 1)</em>
- (or zero when <code>x</code> is zero).
- <p>
- <hr><h3><a name="pdf-math.huge"><code>math.huge</code></a></h3>
- <p>
- The value <code>HUGE_VAL</code>,
- a value larger than or equal to any other numerical value.
- <p>
- <hr><h3><a name="pdf-math.ldexp"><code>math.ldexp (m, e)</code></a></h3>
- <p>
- Returns <em>m2<sup>e</sup></em> (<code>e</code> should be an integer).
- <p>
- <hr><h3><a name="pdf-math.log"><code>math.log (x [, base])</code></a></h3>
- <p>
- Returns the logarithm of <code>x</code> in the given base.
- The default for <code>base</code> is <em>e</em>
- (so that the function returns the natural logarithm of <code>x</code>).
- <p>
- <hr><h3><a name="pdf-math.max"><code>math.max (x, ···)</code></a></h3>
- <p>
- Returns the maximum value among its arguments.
- <p>
- <hr><h3><a name="pdf-math.min"><code>math.min (x, ···)</code></a></h3>
- <p>
- Returns the minimum value among its arguments.
- <p>
- <hr><h3><a name="pdf-math.modf"><code>math.modf (x)</code></a></h3>
- <p>
- Returns two numbers,
- the integral part of <code>x</code> and the fractional part of <code>x</code>.
- <p>
- <hr><h3><a name="pdf-math.pi"><code>math.pi</code></a></h3>
- <p>
- The value of <em>π</em>.
- <p>
- <hr><h3><a name="pdf-math.pow"><code>math.pow (x, y)</code></a></h3>
- <p>
- Returns <em>x<sup>y</sup></em>.
- (You can also use the expression <code>x^y</code> to compute this value.)
- <p>
- <hr><h3><a name="pdf-math.rad"><code>math.rad (x)</code></a></h3>
- <p>
- Returns the angle <code>x</code> (given in degrees) in radians.
- <p>
- <hr><h3><a name="pdf-math.random"><code>math.random ([m [, n]])</code></a></h3>
- <p>
- This function is an interface to the simple
- pseudo-random generator function <code>rand</code> provided by Standard C.
- (No guarantees can be given for its statistical properties.)
- <p>
- When called without arguments,
- returns a uniform pseudo-random real number
- in the range <em>[0,1)</em>.
- When called with an integer number <code>m</code>,
- <code>math.random</code> returns
- a uniform pseudo-random integer in the range <em>[1, m]</em>.
- When called with two integer numbers <code>m</code> and <code>n</code>,
- <code>math.random</code> returns a uniform pseudo-random
- integer in the range <em>[m, n]</em>.
- <p>
- <hr><h3><a name="pdf-math.randomseed"><code>math.randomseed (x)</code></a></h3>
- <p>
- Sets <code>x</code> as the "seed"
- for the pseudo-random generator:
- equal seeds produce equal sequences of numbers.
- <p>
- <hr><h3><a name="pdf-math.sin"><code>math.sin (x)</code></a></h3>
- <p>
- Returns the sine of <code>x</code> (assumed to be in radians).
- <p>
- <hr><h3><a name="pdf-math.sinh"><code>math.sinh (x)</code></a></h3>
- <p>
- Returns the hyperbolic sine of <code>x</code>.
- <p>
- <hr><h3><a name="pdf-math.sqrt"><code>math.sqrt (x)</code></a></h3>
- <p>
- Returns the square root of <code>x</code>.
- (You can also use the expression <code>x^0.5</code> to compute this value.)
- <p>
- <hr><h3><a name="pdf-math.tan"><code>math.tan (x)</code></a></h3>
- <p>
- Returns the tangent of <code>x</code> (assumed to be in radians).
- <p>
- <hr><h3><a name="pdf-math.tanh"><code>math.tanh (x)</code></a></h3>
- <p>
- Returns the hyperbolic tangent of <code>x</code>.
- <h2>6.7 – <a name="6.7">Bitwise Operations</a></h2>
- <p>
- This library provides bitwise operations.
- It provides all its functions inside the table <a name="pdf-bit32"><code>bit32</code></a>.
- <p>
- Unless otherwise stated,
- all functions accept numeric arguments in the range
- <em>(-2<sup>51</sup>,+2<sup>51</sup>)</em>;
- each argument is normalized to
- the remainder of its division by <em>2<sup>32</sup></em>
- and truncated to an integer (in some unspecified way),
- so that its final value falls in the range <em>[0,2<sup>32</sup> - 1]</em>.
- Similarly, all results are in the range <em>[0,2<sup>32</sup> - 1]</em>.
- Note that <code>bit32.bnot(0)</code> is <code>0xFFFFFFFF</code>,
- which is different from <code>-1</code>.
- <p>
- <hr><h3><a name="pdf-bit32.arshift"><code>bit32.arshift (x, disp)</code></a></h3>
- <p>
- Returns the number <code>x</code> shifted <code>disp</code> bits to the right.
- The number <code>disp</code> may be any representable integer.
- Negative displacements shift to the left.
- <p>
- This shift operation is what is called arithmetic shift.
- Vacant bits on the left are filled
- with copies of the higher bit of <code>x</code>;
- vacant bits on the right are filled with zeros.
- In particular,
- displacements with absolute values higher than 31
- result in zero or <code>0xFFFFFFFF</code> (all original bits are shifted out).
- <p>
- <hr><h3><a name="pdf-bit32.band"><code>bit32.band (···)</code></a></h3>
- <p>
- Returns the bitwise <em>and</em> of its operands.
- <p>
- <hr><h3><a name="pdf-bit32.bnot"><code>bit32.bnot (x)</code></a></h3>
- <p>
- Returns the bitwise negation of <code>x</code>.
- For any integer <code>x</code>,
- the following identity holds:
- <pre>
- assert(bit32.bnot(x) == (-1 - x) % 2^32)
- </pre>
- <p>
- <hr><h3><a name="pdf-bit32.bor"><code>bit32.bor (···)</code></a></h3>
- <p>
- Returns the bitwise <em>or</em> of its operands.
- <p>
- <hr><h3><a name="pdf-bit32.btest"><code>bit32.btest (···)</code></a></h3>
- <p>
- Returns a boolean signaling
- whether the bitwise <em>and</em> of its operands is different from zero.
- <p>
- <hr><h3><a name="pdf-bit32.bxor"><code>bit32.bxor (···)</code></a></h3>
- <p>
- Returns the bitwise <em>exclusive or</em> of its operands.
- <p>
- <hr><h3><a name="pdf-bit32.extract"><code>bit32.extract (n, field [, width])</code></a></h3>
- <p>
- Returns the unsigned number formed by the bits
- <code>field</code> to <code>field + width - 1</code> from <code>n</code>.
- Bits are numbered from 0 (least significant) to 31 (most significant).
- All accessed bits must be in the range <em>[0, 31]</em>.
- <p>
- The default for <code>width</code> is 1.
- <p>
- <hr><h3><a name="pdf-bit32.replace"><code>bit32.replace (n, v, field [, width])</code></a></h3>
- <p>
- Returns a copy of <code>n</code> with
- the bits <code>field</code> to <code>field + width - 1</code>
- replaced by the value <code>v</code>.
- See <a href="#pdf-bit32.extract"><code>bit32.extract</code></a> for details about <code>field</code> and <code>width</code>.
- <p>
- <hr><h3><a name="pdf-bit32.lrotate"><code>bit32.lrotate (x, disp)</code></a></h3>
- <p>
- Returns the number <code>x</code> rotated <code>disp</code> bits to the left.
- The number <code>disp</code> may be any representable integer.
- <p>
- For any valid displacement,
- the following identity holds:
- <pre>
- assert(bit32.lrotate(x, disp) == bit32.lrotate(x, disp % 32))
- </pre><p>
- In particular,
- negative displacements rotate to the right.
- <p>
- <hr><h3><a name="pdf-bit32.lshift"><code>bit32.lshift (x, disp)</code></a></h3>
- <p>
- Returns the number <code>x</code> shifted <code>disp</code> bits to the left.
- The number <code>disp</code> may be any representable integer.
- Negative displacements shift to the right.
- In any direction, vacant bits are filled with zeros.
- In particular,
- displacements with absolute values higher than 31
- result in zero (all bits are shifted out).
- <p>
- For positive displacements,
- the following equality holds:
- <pre>
- assert(bit32.lshift(b, disp) == (b * 2^disp) % 2^32)
- </pre>
- <p>
- <hr><h3><a name="pdf-bit32.rrotate"><code>bit32.rrotate (x, disp)</code></a></h3>
- <p>
- Returns the number <code>x</code> rotated <code>disp</code> bits to the right.
- The number <code>disp</code> may be any representable integer.
- <p>
- For any valid displacement,
- the following identity holds:
- <pre>
- assert(bit32.rrotate(x, disp) == bit32.rrotate(x, disp % 32))
- </pre><p>
- In particular,
- negative displacements rotate to the left.
- <p>
- <hr><h3><a name="pdf-bit32.rshift"><code>bit32.rshift (x, disp)</code></a></h3>
- <p>
- Returns the number <code>x</code> shifted <code>disp</code> bits to the right.
- The number <code>disp</code> may be any representable integer.
- Negative displacements shift to the left.
- In any direction, vacant bits are filled with zeros.
- In particular,
- displacements with absolute values higher than 31
- result in zero (all bits are shifted out).
- <p>
- For positive displacements,
- the following equality holds:
- <pre>
- assert(bit32.rshift(b, disp) == math.floor(b % 2^32 / 2^disp))
- </pre>
- <p>
- This shift operation is what is called logical shift.
- <h2>6.8 – <a name="6.8">Input and Output Facilities</a></h2>
- <p>
- The I/O library provides two different styles for file manipulation.
- The first one uses implicit file descriptors;
- that is, there are operations to set a default input file and a
- default output file,
- and all input/output operations are over these default files.
- The second style uses explicit file descriptors.
- <p>
- When using implicit file descriptors,
- all operations are supplied by table <a name="pdf-io"><code>io</code></a>.
- When using explicit file descriptors,
- the operation <a href="#pdf-io.open"><code>io.open</code></a> returns a file descriptor
- and then all operations are supplied as methods of the file descriptor.
- <p>
- The table <code>io</code> also provides
- three predefined file descriptors with their usual meanings from C:
- <a name="pdf-io.stdin"><code>io.stdin</code></a>, <a name="pdf-io.stdout"><code>io.stdout</code></a>, and <a name="pdf-io.stderr"><code>io.stderr</code></a>.
- The I/O library never closes these files.
- <p>
- Unless otherwise stated,
- all I/O functions return <b>nil</b> on failure
- (plus an error message as a second result and
- a system-dependent error code as a third result)
- and some value different from <b>nil</b> on success.
- On non-Posix systems,
- the computation of the error message and error code
- in case of errors
- may be not thread safe,
- because they rely on the global C variable <code>errno</code>.
- <p>
- <hr><h3><a name="pdf-io.close"><code>io.close ([file])</code></a></h3>
- <p>
- Equivalent to <code>file:close()</code>.
- Without a <code>file</code>, closes the default output file.
- <p>
- <hr><h3><a name="pdf-io.flush"><code>io.flush ()</code></a></h3>
- <p>
- Equivalent to <code>io.output():flush()</code>.
- <p>
- <hr><h3><a name="pdf-io.input"><code>io.input ([file])</code></a></h3>
- <p>
- When called with a file name, it opens the named file (in text mode),
- and sets its handle as the default input file.
- When called with a file handle,
- it simply sets this file handle as the default input file.
- When called without parameters,
- it returns the current default input file.
- <p>
- In case of errors this function raises the error,
- instead of returning an error code.
- <p>
- <hr><h3><a name="pdf-io.lines"><code>io.lines ([filename ···])</code></a></h3>
- <p>
- Opens the given file name in read mode
- and returns an iterator function that
- works like <code>file:lines(···)</code> over the opened file.
- When the iterator function detects the end of file,
- it returns <b>nil</b> (to finish the loop) and automatically closes the file.
- <p>
- The call <code>io.lines()</code> (with no file name) is equivalent
- to <code>io.input():lines()</code>;
- that is, it iterates over the lines of the default input file.
- In this case it does not close the file when the loop ends.
- <p>
- In case of errors this function raises the error,
- instead of returning an error code.
- <p>
- <hr><h3><a name="pdf-io.open"><code>io.open (filename [, mode])</code></a></h3>
- <p>
- This function opens a file,
- in the mode specified in the string <code>mode</code>.
- It returns a new file handle,
- or, in case of errors, <b>nil</b> plus an error message.
- <p>
- The <code>mode</code> string can be any of the following:
- <ul>
- <li><b>"<code>r</code>": </b> read mode (the default);</li>
- <li><b>"<code>w</code>": </b> write mode;</li>
- <li><b>"<code>a</code>": </b> append mode;</li>
- <li><b>"<code>r+</code>": </b> update mode, all previous data is preserved;</li>
- <li><b>"<code>w+</code>": </b> update mode, all previous data is erased;</li>
- <li><b>"<code>a+</code>": </b> append update mode, previous data is preserved,
- writing is only allowed at the end of file.</li>
- </ul><p>
- The <code>mode</code> string can also have a '<code>b</code>' at the end,
- which is needed in some systems to open the file in binary mode.
- <p>
- <hr><h3><a name="pdf-io.output"><code>io.output ([file])</code></a></h3>
- <p>
- Similar to <a href="#pdf-io.input"><code>io.input</code></a>, but operates over the default output file.
- <p>
- <hr><h3><a name="pdf-io.popen"><code>io.popen (prog [, mode])</code></a></h3>
- <p>
- This function is system dependent and is not available
- on all platforms.
- <p>
- Starts program <code>prog</code> in a separated process and returns
- a file handle that you can use to read data from this program
- (if <code>mode</code> is <code>"r"</code>, the default)
- or to write data to this program
- (if <code>mode</code> is <code>"w"</code>).
- <p>
- <hr><h3><a name="pdf-io.read"><code>io.read (···)</code></a></h3>
- <p>
- Equivalent to <code>io.input():read(···)</code>.
- <p>
- <hr><h3><a name="pdf-io.tmpfile"><code>io.tmpfile ()</code></a></h3>
- <p>
- Returns a handle for a temporary file.
- This file is opened in update mode
- and it is automatically removed when the program ends.
- <p>
- <hr><h3><a name="pdf-io.type"><code>io.type (obj)</code></a></h3>
- <p>
- Checks whether <code>obj</code> is a valid file handle.
- Returns the string <code>"file"</code> if <code>obj</code> is an open file handle,
- <code>"closed file"</code> if <code>obj</code> is a closed file handle,
- or <b>nil</b> if <code>obj</code> is not a file handle.
- <p>
- <hr><h3><a name="pdf-io.write"><code>io.write (···)</code></a></h3>
- <p>
- Equivalent to <code>io.output():write(···)</code>.
- <p>
- <hr><h3><a name="pdf-file:close"><code>file:close ()</code></a></h3>
- <p>
- Closes <code>file</code>.
- Note that files are automatically closed when
- their handles are garbage collected,
- but that takes an unpredictable amount of time to happen.
- <p>
- When closing a file handle created with <a href="#pdf-io.popen"><code>io.popen</code></a>,
- <a href="#pdf-file:close"><code>file:close</code></a> returns the same values
- returned by <a href="#pdf-os.execute"><code>os.execute</code></a>.
- <p>
- <hr><h3><a name="pdf-file:flush"><code>file:flush ()</code></a></h3>
- <p>
- Saves any written data to <code>file</code>.
- <p>
- <hr><h3><a name="pdf-file:lines"><code>file:lines (···)</code></a></h3>
- <p>
- Returns an iterator function that,
- each time it is called,
- reads the file according to the given formats.
- When no format is given,
- uses "*l" as a default.
- As an example, the construction
- <pre>
- for c in file:lines(1) do <em>body</em> end
- </pre><p>
- will iterate over all characters of the file,
- starting at the current position.
- Unlike <a href="#pdf-io.lines"><code>io.lines</code></a>, this function does not close the file
- when the loop ends.
- <p>
- In case of errors this function raises the error,
- instead of returning an error code.
- <p>
- <hr><h3><a name="pdf-file:read"><code>file:read (···)</code></a></h3>
- <p>
- Reads the file <code>file</code>,
- according to the given formats, which specify what to read.
- For each format,
- the function returns a string (or a number) with the characters read,
- or <b>nil</b> if it cannot read data with the specified format.
- When called without formats,
- it uses a default format that reads the next line
- (see below).
- <p>
- The available formats are
- <ul>
- <li><b>"<code>*n</code>": </b>
- reads a number;
- this is the only format that returns a number instead of a string.
- </li>
- <li><b>"<code>*a</code>": </b>
- reads the whole file, starting at the current position.
- On end of file, it returns the empty string.
- </li>
- <li><b>"<code>*l</code>": </b>
- reads the next line skipping the end of line,
- returning <b>nil</b> on end of file.
- This is the default format.
- </li>
- <li><b>"<code>*L</code>": </b>
- reads the next line keeping the end of line (if present),
- returning <b>nil</b> on end of file.
- </li>
- <li><b><em>number</em>: </b>
- reads a string with up to this number of bytes,
- returning <b>nil</b> on end of file.
- If number is zero,
- it reads nothing and returns an empty string,
- or <b>nil</b> on end of file.
- </li>
- </ul>
- <p>
- <hr><h3><a name="pdf-file:seek"><code>file:seek ([whence [, offset]])</code></a></h3>
- <p>
- Sets and gets the file position,
- measured from the beginning of the file,
- to the position given by <code>offset</code> plus a base
- specified by the string <code>whence</code>, as follows:
- <ul>
- <li><b>"<code>set</code>": </b> base is position 0 (beginning of the file);</li>
- <li><b>"<code>cur</code>": </b> base is current position;</li>
- <li><b>"<code>end</code>": </b> base is end of file;</li>
- </ul><p>
- In case of success, <code>seek</code> returns the final file position,
- measured in bytes from the beginning of the file.
- If <code>seek</code> fails, it returns <b>nil</b>,
- plus a string describing the error.
- <p>
- The default value for <code>whence</code> is <code>"cur"</code>,
- and for <code>offset</code> is 0.
- Therefore, the call <code>file:seek()</code> returns the current
- file position, without changing it;
- the call <code>file:seek("set")</code> sets the position to the
- beginning of the file (and returns 0);
- and the call <code>file:seek("end")</code> sets the position to the
- end of the file, and returns its size.
- <p>
- <hr><h3><a name="pdf-file:setvbuf"><code>file:setvbuf (mode [, size])</code></a></h3>
- <p>
- Sets the buffering mode for an output file.
- There are three available modes:
- <ul>
- <li><b>"<code>no</code>": </b>
- no buffering; the result of any output operation appears immediately.
- </li>
- <li><b>"<code>full</code>": </b>
- full buffering; output operation is performed only
- when the buffer is full or when
- you explicitly <code>flush</code> the file (see <a href="#pdf-io.flush"><code>io.flush</code></a>).
- </li>
- <li><b>"<code>line</code>": </b>
- line buffering; output is buffered until a newline is output
- or there is any input from some special files
- (such as a terminal device).
- </li>
- </ul><p>
- For the last two cases, <code>size</code>
- specifies the size of the buffer, in bytes.
- The default is an appropriate size.
- <p>
- <hr><h3><a name="pdf-file:write"><code>file:write (···)</code></a></h3>
- <p>
- Writes the value of each of its arguments to <code>file</code>.
- The arguments must be strings or numbers.
- <p>
- In case of success, this function returns <code>file</code>.
- Otherwise it returns <b>nil</b> plus a string describing the error.
- <h2>6.9 – <a name="6.9">Operating System Facilities</a></h2>
- <p>
- This library is implemented through table <a name="pdf-os"><code>os</code></a>.
- <p>
- <hr><h3><a name="pdf-os.clock"><code>os.clock ()</code></a></h3>
- <p>
- Returns an approximation of the amount in seconds of CPU time
- used by the program.
- <p>
- <hr><h3><a name="pdf-os.date"><code>os.date ([format [, time]])</code></a></h3>
- <p>
- Returns a string or a table containing date and time,
- formatted according to the given string <code>format</code>.
- <p>
- If the <code>time</code> argument is present,
- this is the time to be formatted
- (see the <a href="#pdf-os.time"><code>os.time</code></a> function for a description of this value).
- Otherwise, <code>date</code> formats the current time.
- <p>
- If <code>format</code> starts with '<code>!</code>',
- then the date is formatted in Coordinated Universal Time.
- After this optional character,
- if <code>format</code> is the string "<code>*t</code>",
- then <code>date</code> returns a table with the following fields:
- <code>year</code> (four digits), <code>month</code> (1–12), <code>day</code> (1–31),
- <code>hour</code> (0–23), <code>min</code> (0–59), <code>sec</code> (0–61),
- <code>wday</code> (weekday, Sunday is 1),
- <code>yday</code> (day of the year),
- and <code>isdst</code> (daylight saving flag, a boolean).
- This last field may be absent
- if the information is not available.
- <p>
- If <code>format</code> is not "<code>*t</code>",
- then <code>date</code> returns the date as a string,
- formatted according to the same rules as the ISO C function <code>strftime</code>.
- <p>
- When called without arguments,
- <code>date</code> returns a reasonable date and time representation that depends on
- the host system and on the current locale
- (that is, <code>os.date()</code> is equivalent to <code>os.date("%c")</code>).
- <p>
- On non-Posix systems,
- this function may be not thread safe
- because of its reliance on C function <code>gmtime</code> and C function <code>localtime</code>.
- <p>
- <hr><h3><a name="pdf-os.difftime"><code>os.difftime (t2, t1)</code></a></h3>
- <p>
- Returns the number of seconds from time <code>t1</code> to time <code>t2</code>.
- In POSIX, Windows, and some other systems,
- this value is exactly <code>t2</code><em>-</em><code>t1</code>.
- <p>
- <hr><h3><a name="pdf-os.execute"><code>os.execute ([command])</code></a></h3>
- <p>
- This function is equivalent to the ISO C function <code>system</code>.
- It passes <code>command</code> to be executed by an operating system shell.
- Its first result is <b>true</b>
- if the command terminated successfully,
- or <b>nil</b> otherwise.
- After this first result
- the function returns a string and a number,
- as follows:
- <ul>
- <li><b>"<code>exit</code>": </b>
- the command terminated normally;
- the following number is the exit status of the command.
- </li>
- <li><b>"<code>signal</code>": </b>
- the command was terminated by a signal;
- the following number is the signal that terminated the command.
- </li>
- </ul>
- <p>
- When called without a <code>command</code>,
- <code>os.execute</code> returns a boolean that is true if a shell is available.
- <p>
- <hr><h3><a name="pdf-os.exit"><code>os.exit ([code [, close])</code></a></h3>
- <p>
- Calls the ISO C function <code>exit</code> to terminate the host program.
- If <code>code</code> is <b>true</b>,
- the returned status is <code>EXIT_SUCCESS</code>;
- if <code>code</code> is <b>false</b>,
- the returned status is <code>EXIT_FAILURE</code>;
- if <code>code</code> is a number,
- the returned status is this number.
- The default value for <code>code</code> is <b>true</b>.
- <p>
- If the optional second argument <code>close</code> is true,
- closes the Lua state before exiting.
- <p>
- <hr><h3><a name="pdf-os.getenv"><code>os.getenv (varname)</code></a></h3>
- <p>
- Returns the value of the process environment variable <code>varname</code>,
- or <b>nil</b> if the variable is not defined.
- <p>
- <hr><h3><a name="pdf-os.remove"><code>os.remove (filename)</code></a></h3>
- <p>
- Deletes the file (or empty directory, on POSIX systems)
- with the given name.
- If this function fails, it returns <b>nil</b>,
- plus a string describing the error and the error code.
- <p>
- <hr><h3><a name="pdf-os.rename"><code>os.rename (oldname, newname)</code></a></h3>
- <p>
- Renames file or directory named <code>oldname</code> to <code>newname</code>.
- If this function fails, it returns <b>nil</b>,
- plus a string describing the error and the error code.
- <p>
- <hr><h3><a name="pdf-os.setlocale"><code>os.setlocale (locale [, category])</code></a></h3>
- <p>
- Sets the current locale of the program.
- <code>locale</code> is a system-dependent string specifying a locale;
- <code>category</code> is an optional string describing which category to change:
- <code>"all"</code>, <code>"collate"</code>, <code>"ctype"</code>,
- <code>"monetary"</code>, <code>"numeric"</code>, or <code>"time"</code>;
- the default category is <code>"all"</code>.
- The function returns the name of the new locale,
- or <b>nil</b> if the request cannot be honored.
- <p>
- If <code>locale</code> is the empty string,
- the current locale is set to an implementation-defined native locale.
- If <code>locale</code> is the string "<code>C</code>",
- the current locale is set to the standard C locale.
- <p>
- When called with <b>nil</b> as the first argument,
- this function only returns the name of the current locale
- for the given category.
- <p>
- This function may be not thread safe
- because of its reliance on C function <code>setlocale</code>.
- <p>
- <hr><h3><a name="pdf-os.time"><code>os.time ([table])</code></a></h3>
- <p>
- Returns the current time when called without arguments,
- or a time representing the date and time specified by the given table.
- This table must have fields <code>year</code>, <code>month</code>, and <code>day</code>,
- and may have fields
- <code>hour</code> (default is 12),
- <code>min</code> (default is 0),
- <code>sec</code> (default is 0),
- and <code>isdst</code> (default is <b>nil</b>).
- For a description of these fields, see the <a href="#pdf-os.date"><code>os.date</code></a> function.
- <p>
- The returned value is a number, whose meaning depends on your system.
- In POSIX, Windows, and some other systems,
- this number counts the number
- of seconds since some given start time (the "epoch").
- In other systems, the meaning is not specified,
- and the number returned by <code>time</code> can be used only as an argument to
- <a href="#pdf-os.date"><code>os.date</code></a> and <a href="#pdf-os.difftime"><code>os.difftime</code></a>.
- <p>
- <hr><h3><a name="pdf-os.tmpname"><code>os.tmpname ()</code></a></h3>
- <p>
- Returns a string with a file name that can
- be used for a temporary file.
- The file must be explicitly opened before its use
- and explicitly removed when no longer needed.
- <p>
- On POSIX systems,
- this function also creates a file with that name,
- to avoid security risks.
- (Someone else might create the file with wrong permissions
- in the time between getting the name and creating the file.)
- You still have to open the file to use it
- and to remove it (even if you do not use it).
- <p>
- When possible,
- you may prefer to use <a href="#pdf-io.tmpfile"><code>io.tmpfile</code></a>,
- which automatically removes the file when the program ends.
- <h2>6.10 – <a name="6.10">The Debug Library</a></h2>
- <p>
- This library provides
- the functionality of the debug interface (<a href="#4.9">§4.9</a>) to Lua programs.
- You should exert care when using this library.
- Several of its functions
- violate basic assumptions about Lua code
- (e.g., that variables local to a function
- cannot be accessed from outside;
- that userdata metatables cannot be changed by Lua code;
- that Lua programs do not crash)
- and therefore can compromise otherwise secure code.
- Moreover, some functions in this library may be slow.
- <p>
- All functions in this library are provided
- inside the <a name="pdf-debug"><code>debug</code></a> table.
- All functions that operate over a thread
- have an optional first argument which is the
- thread to operate over.
- The default is always the current thread.
- <p>
- <hr><h3><a name="pdf-debug.debug"><code>debug.debug ()</code></a></h3>
- <p>
- Enters an interactive mode with the user,
- running each string that the user enters.
- Using simple commands and other debug facilities,
- the user can inspect global and local variables,
- change their values, evaluate expressions, and so on.
- A line containing only the word <code>cont</code> finishes this function,
- so that the caller continues its execution.
- <p>
- Note that commands for <code>debug.debug</code> are not lexically nested
- within any function and so have no direct access to local variables.
- <p>
- <hr><h3><a name="pdf-debug.gethook"><code>debug.gethook ([thread])</code></a></h3>
- <p>
- Returns the current hook settings of the thread, as three values:
- the current hook function, the current hook mask,
- and the current hook count
- (as set by the <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> function).
- <p>
- <hr><h3><a name="pdf-debug.getinfo"><code>debug.getinfo ([thread,] f [, what])</code></a></h3>
- <p>
- Returns a table with information about a function.
- You can give the function directly
- or you can give a number as the value of <code>f</code>,
- which means the function running at level <code>f</code> of the call stack
- of the given thread:
- level 0 is the current function (<code>getinfo</code> itself);
- level 1 is the function that called <code>getinfo</code>
- (except for tail calls, which do not count on the stack);
- and so on.
- If <code>f</code> is a number larger than the number of active functions,
- then <code>getinfo</code> returns <b>nil</b>.
- <p>
- The returned table can contain all the fields returned by <a href="#lua_getinfo"><code>lua_getinfo</code></a>,
- with the string <code>what</code> describing which fields to fill in.
- The default for <code>what</code> is to get all information available,
- except the table of valid lines.
- If present,
- the option '<code>f</code>'
- adds a field named <code>func</code> with the function itself.
- If present,
- the option '<code>L</code>'
- adds a field named <code>activelines</code> with the table of
- valid lines.
- <p>
- For instance, the expression <code>debug.getinfo(1,"n").name</code> returns
- a table with a name for the current function,
- if a reasonable name can be found,
- and the expression <code>debug.getinfo(print)</code>
- returns a table with all available information
- about the <a href="#pdf-print"><code>print</code></a> function.
- <p>
- <hr><h3><a name="pdf-debug.getlocal"><code>debug.getlocal ([thread,] f, local)</code></a></h3>
- <p>
- This function returns the name and the value of the local variable
- with index <code>local</code> of the function at level <code>f</code> of the stack.
- This function accesses not only explicit local variables,
- but also parameters, temporaries, etc.
- <p>
- The first parameter or local variable has index 1, and so on,
- until the last active variable.
- Negative indices refer to vararg parameters;
- -1 is the first vararg parameter.
- The function returns <b>nil</b> if there is no variable with the given index,
- and raises an error when called with a level out of range.
- (You can call <a href="#pdf-debug.getinfo"><code>debug.getinfo</code></a> to check whether the level is valid.)
- <p>
- Variable names starting with '<code>(</code>' (open parenthesis)
- represent internal variables
- (loop control variables, temporaries, varargs, and C function locals).
- <p>
- The parameter <code>f</code> may also be a function.
- In that case, <code>getlocal</code> returns only the name of function parameters.
- <p>
- <hr><h3><a name="pdf-debug.getmetatable"><code>debug.getmetatable (value)</code></a></h3>
- <p>
- Returns the metatable of the given <code>value</code>
- or <b>nil</b> if it does not have a metatable.
- <p>
- <hr><h3><a name="pdf-debug.getregistry"><code>debug.getregistry ()</code></a></h3>
- <p>
- Returns the registry table (see <a href="#4.5">§4.5</a>).
- <p>
- <hr><h3><a name="pdf-debug.getupvalue"><code>debug.getupvalue (f, up)</code></a></h3>
- <p>
- This function returns the name and the value of the upvalue
- with index <code>up</code> of the function <code>f</code>.
- The function returns <b>nil</b> if there is no upvalue with the given index.
- <p>
- <hr><h3><a name="pdf-debug.getuservalue"><code>debug.getuservalue (u)</code></a></h3>
- <p>
- Returns the Lua value associated to <code>u</code>.
- If <code>u</code> is not a userdata,
- returns <b>nil</b>.
- <p>
- <hr><h3><a name="pdf-debug.sethook"><code>debug.sethook ([thread,] hook, mask [, count])</code></a></h3>
- <p>
- Sets the given function as a hook.
- The string <code>mask</code> and the number <code>count</code> describe
- when the hook will be called.
- The string mask may have any combination of the following characters,
- with the given meaning:
- <ul>
- <li><b>'<code>c</code>': </b> the hook is called every time Lua calls a function;</li>
- <li><b>'<code>r</code>': </b> the hook is called every time Lua returns from a function;</li>
- <li><b>'<code>l</code>': </b> the hook is called every time Lua enters a new line of code.</li>
- </ul><p>
- Moreover,
- with a <code>count</code> different from zero,
- the hook is called also after every <code>count</code> instructions.
- <p>
- When called without arguments,
- <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> turns off the hook.
- <p>
- When the hook is called, its first parameter is a string
- describing the event that has triggered its call:
- <code>"call"</code> (or <code>"tail call"</code>),
- <code>"return"</code>,
- <code>"line"</code>, and <code>"count"</code>.
- For line events,
- the hook also gets the new line number as its second parameter.
- Inside a hook,
- you can call <code>getinfo</code> with level 2 to get more information about
- the running function
- (level 0 is the <code>getinfo</code> function,
- and level 1 is the hook function).
- <p>
- <hr><h3><a name="pdf-debug.setlocal"><code>debug.setlocal ([thread,] level, local, value)</code></a></h3>
- <p>
- This function assigns the value <code>value</code> to the local variable
- with index <code>local</code> of the function at level <code>level</code> of the stack.
- The function returns <b>nil</b> if there is no local
- variable with the given index,
- and raises an error when called with a <code>level</code> out of range.
- (You can call <code>getinfo</code> to check whether the level is valid.)
- Otherwise, it returns the name of the local variable.
- <p>
- See <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for more information about
- variable indices and names.
- <p>
- <hr><h3><a name="pdf-debug.setmetatable"><code>debug.setmetatable (value, table)</code></a></h3>
- <p>
- Sets the metatable for the given <code>value</code> to the given <code>table</code>
- (which can be <b>nil</b>).
- Returns <code>value</code>.
- <p>
- <hr><h3><a name="pdf-debug.setupvalue"><code>debug.setupvalue (f, up, value)</code></a></h3>
- <p>
- This function assigns the value <code>value</code> to the upvalue
- with index <code>up</code> of the function <code>f</code>.
- The function returns <b>nil</b> if there is no upvalue
- with the given index.
- Otherwise, it returns the name of the upvalue.
- <p>
- <hr><h3><a name="pdf-debug.setuservalue"><code>debug.setuservalue (udata, value)</code></a></h3>
- <p>
- Sets the given <code>value</code> as
- the Lua value associated to the given <code>udata</code>.
- <code>value</code> must be a table or <b>nil</b>;
- <code>udata</code> must be a full userdata.
- <p>
- Returns <code>udata</code>.
- <p>
- <hr><h3><a name="pdf-debug.traceback"><code>debug.traceback ([thread,] [message [, level]])</code></a></h3>
- <p>
- If <code>message</code> is present but is neither a string nor <b>nil</b>,
- this function returns <code>message</code> without further processing.
- Otherwise,
- it returns a string with a traceback of the call stack.
- An optional <code>message</code> string is appended
- at the beginning of the traceback.
- An optional <code>level</code> number tells at which level
- to start the traceback
- (default is 1, the function calling <code>traceback</code>).
- <p>
- <hr><h3><a name="pdf-debug.upvalueid"><code>debug.upvalueid (f, n)</code></a></h3>
- <p>
- Returns an unique identifier (as a light userdata)
- for the upvalue numbered <code>n</code>
- from the given function.
- <p>
- These unique identifiers allow a program to check whether different
- closures share upvalues.
- Lua closures that share an upvalue
- (that is, that access a same external local variable)
- will return identical ids for those upvalue indices.
- <p>
- <hr><h3><a name="pdf-debug.upvaluejoin"><code>debug.upvaluejoin (f1, n1, f2, n2)</code></a></h3>
- <p>
- Make the <code>n1</code>-th upvalue of the Lua closure <code>f1</code>
- refer to the <code>n2</code>-th upvalue of the Lua closure <code>f2</code>.
- <h1>7 – <a name="7">Lua Standalone</a></h1>
- <p>
- Although Lua has been designed as an extension language,
- to be embedded in a host C program,
- it is also frequently used as a standalone language.
- An interpreter for Lua as a standalone language,
- called simply <code>lua</code>,
- is provided with the standard distribution.
- The standalone interpreter includes
- all standard libraries, including the debug library.
- Its usage is:
- <pre>
- lua [options] [script [args]]
- </pre><p>
- The options are:
- <ul>
- <li><b><code>-e <em>stat</em></code>: </b> executes string <em>stat</em>;</li>
- <li><b><code>-l <em>mod</em></code>: </b> "requires" <em>mod</em>;</li>
- <li><b><code>-i</code>: </b> enters interactive mode after running <em>script</em>;</li>
- <li><b><code>-v</code>: </b> prints version information;</li>
- <li><b><code>-E</code>: </b> ignores environment variables;</li>
- <li><b><code>--</code>: </b> stops handling options;</li>
- <li><b><code>-</code>: </b> executes <code>stdin</code> as a file and stops handling options.</li>
- </ul><p>
- After handling its options, <code>lua</code> runs the given <em>script</em>,
- passing to it the given <em>args</em> as string arguments.
- When called without arguments,
- <code>lua</code> behaves as <code>lua -v -i</code>
- when the standard input (<code>stdin</code>) is a terminal,
- and as <code>lua -</code> otherwise.
- <p>
- When called without option <code>-E</code>,
- the interpreter checks for an environment variable <a name="pdf-LUA_INIT_5_2"><code>LUA_INIT_5_2</code></a>
- (or <a name="pdf-LUA_INIT"><code>LUA_INIT</code></a> if it is not defined)
- before running any argument.
- If the variable content has the format <code>@<em>filename</em></code>,
- then <code>lua</code> executes the file.
- Otherwise, <code>lua</code> executes the string itself.
- <p>
- When called with option <code>-E</code>,
- besides ignoring <code>LUA_INIT</code>,
- Lua also ignores
- the values of <code>LUA_PATH</code> and <code>LUA_CPATH</code>,
- setting the values of
- <a href="#pdf-package.path"><code>package.path</code></a> and <a href="#pdf-package.cpath"><code>package.cpath</code></a>
- with the default paths defined in <code>luaconf.h</code>.
- <p>
- All options are handled in order, except <code>-i</code> and <code>-E</code>.
- For instance, an invocation like
- <pre>
- $ lua -e'a=1' -e 'print(a)' script.lua
- </pre><p>
- will first set <code>a</code> to 1, then print the value of <code>a</code>,
- and finally run the file <code>script.lua</code> with no arguments.
- (Here <code>$</code> is the shell prompt. Your prompt may be different.)
- <p>
- Before starting to run the script,
- <code>lua</code> collects all arguments in the command line
- in a global table called <code>arg</code>.
- The script name is stored at index 0,
- the first argument after the script name goes to index 1,
- and so on.
- Any arguments before the script name
- (that is, the interpreter name plus the options)
- go to negative indices.
- For instance, in the call
- <pre>
- $ lua -la b.lua t1 t2
- </pre><p>
- the interpreter first runs the file <code>a.lua</code>,
- then creates a table
- <pre>
- arg = { [-2] = "lua", [-1] = "-la",
- [0] = "b.lua",
- [1] = "t1", [2] = "t2" }
- </pre><p>
- and finally runs the file <code>b.lua</code>.
- The script is called with <code>arg[1]</code>, <code>arg[2]</code>, ...
- as arguments;
- it can also access these arguments with the vararg expression '<code>...</code>'.
- <p>
- In interactive mode,
- if you write an incomplete statement,
- the interpreter waits for its completion
- by issuing a different prompt.
- <p>
- In case of unprotected errors in the script,
- the interpreter reports the error to the standard error stream.
- If the error object is a string,
- the interpreter adds a stack traceback to it.
- Otherwise, if the error object has a metamethod <code>__tostring</code>,
- the interpreter calls this metamethod to produce the final message.
- Finally, if the error object is <b>nil</b>,
- the interpreter does not report the error.
- <p>
- When finishing normally,
- the interpreter closes its main Lua state
- (see <a href="#lua_close"><code>lua_close</code></a>).
- The script can avoid this step by
- calling <a href="#pdf-os.exit"><code>os.exit</code></a> to terminate.
- <p>
- To allow the use of Lua as a
- script interpreter in Unix systems,
- the standalone interpreter skips
- the first line of a chunk if it starts with <code>#</code>.
- Therefore, Lua scripts can be made into executable programs
- by using <code>chmod +x</code> and the <code>#!</code> form,
- as in
- <pre>
- #!/usr/local/bin/lua
- </pre><p>
- (Of course,
- the location of the Lua interpreter may be different in your machine.
- If <code>lua</code> is in your <code>PATH</code>,
- then
- <pre>
- #!/usr/bin/env lua
- </pre><p>
- is a more portable solution.)
- <h1>8 – <a name="8">Incompatibilities with the Previous Version</a></h1>
- <p>
- Here we list the incompatibilities that you may find when moving a program
- from Lua 5.1 to Lua 5.2.
- You can avoid some incompatibilities by compiling Lua with
- appropriate options (see file <code>luaconf.h</code>).
- However,
- all these compatibility options will be removed in the next version of Lua.
- Similarly,
- all features marked as deprecated in Lua 5.1
- have been removed in Lua 5.2.
- <h2>8.1 – <a name="8.1">Changes in the Language</a></h2>
- <ul>
- <li>
- The concept of <em>environment</em> changed.
- Only Lua functions have environments.
- To set the environment of a Lua function,
- use the variable <code>_ENV</code> or the function <a href="#pdf-load"><code>load</code></a>.
- <p>
- C functions no longer have environments.
- Use an upvalue with a shared table if you need to keep
- shared state among several C functions.
- (You may use <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a> to open a C library
- with all functions sharing a common upvalue.)
- <p>
- To manipulate the "environment" of a userdata
- (which is now called user value),
- use the new functions
- <a href="#lua_getuservalue"><code>lua_getuservalue</code></a> and <a href="#lua_setuservalue"><code>lua_setuservalue</code></a>.
- </li>
- <li>
- Lua identifiers cannot use locale-dependent letters.
- </li>
- <li>
- Doing a step or a full collection in the garbage collector
- does not restart the collector if it has been stopped.
- </li>
- <li>
- Weak tables with weak keys now perform like <em>ephemeron tables</em>.
- </li>
- <li>
- The event <em>tail return</em> in debug hooks was removed.
- Instead, tail calls generate a special new event,
- <em>tail call</em>, so that the debugger can know that
- there will not be a corresponding return event.
- </li>
- <li>
- Equality between function values has changed.
- Now, a function definition may not create a new value;
- it may reuse some previous value if there is no
- observable difference to the new function.
- </li>
- </ul>
- <h2>8.2 – <a name="8.2">Changes in the Libraries</a></h2>
- <ul>
- <li>
- Function <code>module</code> is deprecated.
- It is easy to set up a module with regular Lua code.
- Modules are not expected to set global variables.
- </li>
- <li>
- Functions <code>setfenv</code> and <code>getfenv</code> were removed,
- because of the changes in environments.
- </li>
- <li>
- Function <code>math.log10</code> is deprecated.
- Use <a href="#pdf-math.log"><code>math.log</code></a> with 10 as its second argument, instead.
- </li>
- <li>
- Function <code>loadstring</code> is deprecated.
- Use <code>load</code> instead; it now accepts string arguments
- and are exactly equivalent to <code>loadstring</code>.
- </li>
- <li>
- Function <code>table.maxn</code> is deprecated.
- Write it in Lua if you really need it.
- </li>
- <li>
- Function <code>os.execute</code> now returns <b>true</b> when command
- terminates successfully and <b>nil</b> plus error information
- otherwise.
- </li>
- <li>
- Function <code>unpack</code> was moved into the table library
- and therefore must be called as <a href="#pdf-table.unpack"><code>table.unpack</code></a>.
- </li>
- <li>
- Character class <code>%z</code> in patterns is deprecated,
- as now patterns may contain '<code>\0</code>' as a regular character.
- </li>
- <li>
- The table <code>package.loaders</code> was renamed <code>package.searchers</code>.
- </li>
- <li>
- Lua does not have bytecode verification anymore.
- So, all functions that load code
- (<a href="#pdf-load"><code>load</code></a> and <a href="#pdf-loadfile"><code>loadfile</code></a>)
- are potentially insecure when loading untrusted binary data.
- (Actually, those functions were already insecure because
- of flaws in the verification algorithm.)
- When in doubt,
- use the <code>mode</code> argument of those functions
- to restrict them to loading textual chunks.
- </li>
- <li>
- The standard paths in the official distribution may
- change between versions.
- </li>
- </ul>
- <h2>8.3 – <a name="8.3">Changes in the API</a></h2>
- <ul>
- <li>
- Pseudoindex <code>LUA_GLOBALSINDEX</code> was removed.
- You must get the global environment from the registry
- (see <a href="#4.5">§4.5</a>).
- </li>
- <li>
- Pseudoindex <code>LUA_ENVIRONINDEX</code>
- and functions <code>lua_getfenv</code>/<code>lua_setfenv</code>
- were removed,
- as C functions no longer have environments.
- </li>
- <li>
- Function <code>luaL_register</code> is deprecated.
- Use <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a> so that your module does not create globals.
- (Modules are not expected to set global variables anymore.)
- </li>
- <li>
- The <code>osize</code> argument to the allocation function
- may not be zero when creating a new block,
- that is, when <code>ptr</code> is <code>NULL</code>
- (see <a href="#lua_Alloc"><code>lua_Alloc</code></a>).
- Use only the test <code>ptr == NULL</code> to check whether
- the block is new.
- </li>
- <li>
- Finalizers (<code>__gc</code> metamethods) for userdata are called in the
- reverse order that they were marked for finalization,
- not that they were created (see <a href="#2.5.1">§2.5.1</a>).
- (Most userdata are marked immediately after they are created.)
- Moreover,
- if the metatable does not have a <code>__gc</code> field when set,
- the finalizer will not be called,
- even if it is set later.
- </li>
- <li>
- <code>luaL_typerror</code> was removed.
- Write your own version if you need it.
- </li>
- <li>
- Function <code>lua_cpcall</code> is deprecated.
- You can simply push the function with <a href="#lua_pushcfunction"><code>lua_pushcfunction</code></a>
- and call it with <a href="#lua_pcall"><code>lua_pcall</code></a>.
- </li>
- <li>
- Functions <code>lua_equal</code> and <code>lua_lessthan</code> are deprecated.
- Use the new <a href="#lua_compare"><code>lua_compare</code></a> with appropriate options instead.
- </li>
- <li>
- Function <code>lua_objlen</code> was renamed <a href="#lua_rawlen"><code>lua_rawlen</code></a>.
- </li>
- <li>
- Function <a href="#lua_load"><code>lua_load</code></a> has an extra parameter, <code>mode</code>.
- Pass <code>NULL</code> to simulate the old behavior.
- </li>
- <li>
- Function <a href="#lua_resume"><code>lua_resume</code></a> has an extra parameter, <code>from</code>.
- Pass <code>NULL</code> or the thread doing the call.
- </li>
- </ul>
- <h1>9 – <a name="9">The Complete Syntax of Lua</a></h1>
- <p>
- Here is the complete syntax of Lua in extended BNF.
- (It does not describe operator precedences.)
- <pre>
- chunk ::= block
- block ::= {stat} [retstat]
- stat ::= ‘<b>;</b>’ |
- varlist ‘<b>=</b>’ explist |
- functioncall |
- label |
- <b>break</b> |
- <b>goto</b> Name |
- <b>do</b> block <b>end</b> |
- <b>while</b> exp <b>do</b> block <b>end</b> |
- <b>repeat</b> block <b>until</b> exp |
- <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> |
- <b>for</b> Name ‘<b>=</b>’ exp ‘<b>,</b>’ exp [‘<b>,</b>’ exp] <b>do</b> block <b>end</b> |
- <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> |
- <b>function</b> funcname funcbody |
- <b>local</b> <b>function</b> Name funcbody |
- <b>local</b> namelist [‘<b>=</b>’ explist]
- retstat ::= <b>return</b> [explist] [‘<b>;</b>’]
- label ::= ‘<b>::</b>’ Name ‘<b>::</b>’
- funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name]
- varlist ::= var {‘<b>,</b>’ var}
- var ::= Name | prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’ | prefixexp ‘<b>.</b>’ Name
- namelist ::= Name {‘<b>,</b>’ Name}
- explist ::= exp {‘<b>,</b>’ exp}
- exp ::= <b>nil</b> | <b>false</b> | <b>true</b> | Number | String | ‘<b>...</b>’ | functiondef |
- prefixexp | tableconstructor | exp binop exp | unop exp
- prefixexp ::= var | functioncall | ‘<b>(</b>’ exp ‘<b>)</b>’
- functioncall ::= prefixexp args | prefixexp ‘<b>:</b>’ Name args
- args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’ | tableconstructor | String
- functiondef ::= <b>function</b> funcbody
- funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b>
- parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] | ‘<b>...</b>’
- tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’
- fieldlist ::= field {fieldsep field} [fieldsep]
- field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp | Name ‘<b>=</b>’ exp | exp
- fieldsep ::= ‘<b>,</b>’ | ‘<b>;</b>’
- binop ::= ‘<b>+</b>’ | ‘<b>-</b>’ | ‘<b>*</b>’ | ‘<b>/</b>’ | ‘<b>^</b>’ | ‘<b>%</b>’ | ‘<b>..</b>’ |
- ‘<b><</b>’ | ‘<b><=</b>’ | ‘<b>></b>’ | ‘<b>>=</b>’ | ‘<b>==</b>’ | ‘<b>~=</b>’ |
- <b>and</b> | <b>or</b>
- unop ::= ‘<b>-</b>’ | <b>not</b> | ‘<b>#</b>’
- </pre>
- <p>
- <HR>
- <SMALL CLASS="footer">
- Last update:
- Mon Feb 23 22:24:44 BRT 2015
- </SMALL>
- <!--
- Last change: revised for Lua 5.2.4
- -->
- </body></html>
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