This document ============= This document is a guide how to develop GNU Midnight Commander. It's quite incomplete, but may be worth reading anyway. The document was written by Miguel de Icaza and reworked by Pavel Roskin and later from Patrick Winnertz. Some parts were taken from the messages posted in the mailing lists. Compiling from GIT ================== The full list of requirements is listed in the INSTALL file. It is recommended that all those tools are installed with the same prefix. Make sure that the tools with the right version are first in PATH. Once you have the right tools, run `autogen.sh' - it will generate everything necessary for the build `configure'. Then run 'configure' and `make' as usually. The distribution tarball is created by the command `make distcheck'. This command can take a while. Currently snapshots are made on Debian unstable and use the versions of the tools from the unstable repository. Yes, the rpm packages are made on Debian too. Note that the version of gettext doesn't affect the snapshot because the distributed files are installed by gettext from archives for the version used in the AM_GNU_GETTEXT_VERSION macro, which is 0.18.2. Working with GNU Midnight Commander =================================== Please use the GIT version. It may be quite different from the released versions. A lot of cleanup is going on. The GIT version may be easier to understand, in addition to the obvious fact that the merging is easier with the GIT version. In order to compile GNU Midnight Commander from a clean GIT checkout you should use 'autogen.sh && ./configure' instead of 'configure'. GNU Midnight Commander uses Autoconf and Automake, with make it fairly portable. However, GNU Make is strongly recommended for development because other versions of make may not track dependencies properly. This is very important for correct compilation, especially if you change any header files. If you add or remove any files, please change Makefile.am in the same directory accordingly. When doing significant changes in the tree structure, "make distcheck" is strongly recommended. GNU Autoconf allows you to test several different configurations are once. To do so, use the so called out-of-tree (or VPATH) compilation. Create separate empty directories and run configure with full path from those directories, like this: cd /usr/local/src mkdir mc-slang mkdir mc-ncurses cd mc-slang /usr/local/src/mc/configure && make all cd ../mc-ncurses /usr/local/src/mc/configure --with-screen=ncurses && make all Please use the same indentation as other developers. To indent a block, select in the internal editor and use Shift-F9 to call the external indent. For historic reasons, GNU Midnight Commander used formatting that is not default for GNU Indent. Please put following text to your ~/.indent.pro file to make GNU Indent follow the style used in GNU Midnight Commander: --gnu-style --format-first-column-comments --indent-level4 --brace-indent0 --line-length100 --no-tabs --blank-lines-after-procedures or in short notation: indent -gnu -fc1 -i4 -bli0 -nut -bap -l100 It's OK to indent the whole function if you edit it. However, please refrain from it if you are posting your patch for review. In this case you would save time of other developers if you only include significant changes. The developer applying your patch can format the code for you. Please keep in mind that the VFS subsystem is licensed under LGPL, while the rest of the code uses GPL. Code structure - outline ======================== The code is located in following directories. vfs - Virtual File System. This library provides filesystem-like access to various data, such are archives and remote filesystems. To use VFS, you should use wrappers around POSIX calls. The wrappers have names composed from "mc_" and the standard name of the function. For example, to open a file on VFS, use mc_open() instead. edit - the internal editor. This code has been contributed by Paul Sheer, the author of Cooledit. The internal editor shares some code with Cooledit, but now it's developed as part of GNU Midnight Commander. src - the main part of the code. This code includes the dialog manager written by Radek Doulik and source code of the main application. Code structure - details ======================== GNU Midnight Commander uses extensively the dialog manager written by Radek Doulik. To understand how the dialog manager works, please read the dialog.c. You will find the basic widgets in the files widget.c. Some more high-level functions, e.g. to display a message box, are located in wtools.c. This file also contains the Quick Dialog code, which makes it easier to create complex dialogs. The files util.c and utilunix.c have a lot of utility functions. Get familiar with them, they are very simple. glib is used for memory allocation and for some utility functions, such as manipulation with lists and trees. gmodule (part of the glib distribution) is used to load some libraries dynamically at the run time. Thanks to glib, the code has almost no hardcoded limits, since there are many ways to avoid them. For example, when you want to concatenate strings, use the g_strconcat() function: new_text = g_strconcat (username, " ", password, (char *)0); This allocates new memory for the string, so you should use g_free() on the result. The parent of all dialogs is called midnight_dlg. Both panels are widgets in that dialog. Other widgets include the menu, the command line and the button bar. Input handling ============== The routines for input handling on the Midnight Commander are: getch, get_key_code, mi_getch and get_event. getch is an interface to the low level system input mechanism. It does not deal with the mouse. In the case of ncurses, this is a function implemented in the ncurses library that translates key sequences to key codes (\E[A to something like KEY_UP and so on). In the case of S-Lang there is no such conversion, that's why we load a set of extra definitions. The get_key_code routine converts the data from getch to the constants the Midnight Commander uses. In the case of S-Lang, it will actually do all the jobs that getch does for curses. In the case of curses it patches a couple of sequences that are not available on some terminal databases. This routine is the one you want to use if you want a character without the mouse support. get_event is the routine you want to use if you want to handle mouse events, it will return 0 on a mouse event, -1 if no input is available or a key code if there is some input available. This routine in turn uses get_key_code to decode the input stream and convert it to useful constants. mi_getch is just a wrapper around get_event that ignores all the mouse events. It's used only in a couple of places, this routine may return -1 if no input is available (if you have set the nodelay option of ncurses or S-Lang with nodelay) or a character code if no such option is available. Mouse support ============= The mouse support in the Midnight Commander is based on the get_event routine. The core of the mouse event dispatching is in the dlg.c:run_dlg routine. ncurses ======= Although S-Lang is now used by default, we still support ncurses. We basically are using a small subset of ncurses because we want to be compatible with Slang. The Dialog manager and the Widgets ================================== The Dialog manager and the Widget structure are implemented in src/dialog.c. Everything shown on screen is a dialog. Dialogs contain widgets, but not everything on screen is a widget. Dialogs can draw themselves. Dialogs are connected into a singly linked list using "parent" field. Currently active dialog is saved in current_dlg variable. The toplevel dialog has parent NULL. Usually it's midnight_dlg. parent parent current_dlg ------->another dialog-- ... -->midnight_dlg When the screen needs to be refreshed, every dialog asks its parent to refresh first, and then refreshes itself. A dialog is created by create_dlg(). Then it's populated by widgets using add_widget(). Then the dialog is run by calling run_dlg(), which returns the id of the button selected by the user. Finally, the dialog is destroyed by calling destroy_dlg(). Widgets are placed to a doubly linked circular list. Each widget has previous and next widget. prev next prev next widget1 <---------> widget2 <---------> widget3 ^ ^ ----------------------------------------- next prev Pressing Tab moves focus to the "next" widget, pressing Shift-Tab moves focus to "prev". The tab order is equal to the add order except some old code that use the reverse order by setting DLG_REVERSE flag in create_dlg() call. Please don't use reverse order in the new code. The initial widget to get focus can be selected by calling dlg_select_widget(). When creating a dialog, you may want to use a callback that would intercept some dialog events. However, many widgets will do the right thing by default, so some dialogs can work just fine without callbacks. There are also widget events, which are sent by the dialog to individual widgets. Some widgets also have user callbacks. To create your own widget, use init_widget(). In this case, you must provide a callback function. Please note that it's not the same as the user callback in some widgets. Where to Find Bug Reports and Patches ===================================== The official place for bug reports is: https://www.midnight-commander.org/ There are various unofficial sources where bug reports and patches can be found (NOT maintained by the MC team). http://bugs.debian.org/mc The bug tracking system for Debian, a package collection mainly for GNU/Linux and the Hurd. http://bugzilla.redhat.com/bugzilla/buglist.cgi?component=mc Bugs reported in Redhat Linux. http://www.openbsd.org/cgi-bin/cvsweb/ports/misc/mc/patches/ The patches that are applied for the OpenBSD version of MC. http://www.freebsd.org/cgi/cvsweb.cgi/ports/misc/mc/files/ The patches that are applied for the FreeBSD version of MC. http://cvsweb.netbsd.org/bsdweb.cgi/pkgsrc/sysutils/mc/patches/ The patches that are applied for the NetBSD version of MC. http://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-x86/app-misc/mc/files/?hideattic=1 The patches that are applied for the Gentoo Linux version of MC. Programming Tips ================ (This list should be sorted alphabetically.) ?: This operator has a precedence that is easy to use the wrong way. You might think that int right = 25 + have_frame() ? 1 : 0; /* WRONG */ results in either 25 or 26. This is not the case. The C compiler sees this as: int right = (25 + have_frame()) ? 1 : 0; /* WRONG */ To avoid this, put the ?: in parentheses, like this int right = 25 + (have_frame() ? 1 : 0); /* RIGHT */ If the condition is more complicated, put it in additional parentheses: int right = 25 + ((have_frame()) ? 1 : 0); /* RIGHT */ const: For every function taking a string argument, decide whether you (as a user of the function) would expect that the string is modi- fied by the function. If not, declare the string argument as "const char *". If your implementation needs to modify the string, use g_strdup to create a local copy. const_cast: Has been replaced by str_unconst. g_free: g_free handles NULL argument too, no need for the comparison. Bad way: if (old_dir) g_free (old_dir); Right way: g_free (old_dir); g_strdup: When you use g_strdup to create a local copy of a string, use the following pattern to keep the reference. char * const pathref = g_strdup(argument); /* ... */ g_free (pathref); The "const" will make the pointer unmodifiable (pathref++ is not possible), but you can still modify the string contents. NULL: When you pass NULL as an argument of a varargs function, cast the 0 to the appropriate data type. If a system #defines NULL to be 0 (at least NetBSD and OpenBSD do), and the sizes of int and a pointer are different, the argument will be passed as int 0, not as a pointer. This tip applies at least to catstrs (edit/edit.h), execl(3), execle(3), execlp(3), g_strconcat (glib), parent_call (src/background.h), parent_call_string (src/background.h). example: char *path = g_strconcat("dir", "/", "file", (char *)0); size_t: This data type is suitable for expressing sizes of memory or the length of strings. This type is unsigned, so you need not check if the value is >= 0. strncpy: Don't use this function in newly created code. It is slow, insecure and hard to use. A much better alternative is g_strlcpy (see there). str_unconst: We use many libraries that do not know about "const char *" and thus declare their functions to require "char *". If you know for sure that an external function does not modify the string, you can "unconst" a string using the function str_unconst(). If you are not sure whether the function modifies the string, you should use g_strdup() to pass a copy of a string to the function. Don't forget to call g_free() after work is done. unused: Unused arguments of a function can be marked like this: void do_nothing(int data) { (void) &data; } This tells the GNU C Compiler not to emit a warning, and has no side effects for other compilers.