Version 21 (modified by martinl, 6 years ago) (diff)


Please improve this list...

Dear (new) GRASS developer,

when submitting C code to GRASS SVN repository, please take care of following rules:

  1. Get and read the GRASS Programmer's Manual here:

Or generate it from this source code (the programmer's manual is integrated in the source code in doxygen style):

      make htmldocs
      make pdfdocs
  1. Use the directory structure to place your module appropriately into the source tree
  • libraries go into lib/
  • raster modules go into raster/
  • vector modules go into vector/
  • ...

Consider to take a look at "GNU Coding Standards":

  1. Add a header section to each file you submit and make sure you

include the copyright. The purpose section is meant to contain a general overview of the code in the file to assist other programmers that will need to make changes to your code. If you are modifying an existing file you may under no circumstances remove prior copyright or licensing text that is not your own, even for a major rewrite. If any original code or code that is in part derived from another's original work remains, it must be properly cited.

Example (ficticious header for a file called color.c) :

 * AUTHOR(S):    John Doe <jdoe at somewhere org>
 * PURPOSE:      Provide short description of module here...
 * COPYRIGHT:    (C) 2010 by John Doe, and the GRASS Development Team
 *               This program is free software under the GNU General Public
 *               License (>=v2). Read the COPYING file that comes with GRASS
 *               for details.

The copyright protects your rights according to GNU General Public License (

  1. We don't want the $ID$ in source code any more as it causes problems

for the SVN branches.

  1. To ensure that the software system continues to work, please include
    	#include <grass/config.h>

in your files and make use of the various system dependencies contained therein. As one example of this, see source:grass/trunk/lib/gmath/fft.c. Please refrain from declaring system functions within the software; include the proper header files (conditionally dependent on config.h macros if necessary) instead.

  1. Order of include headers

In general, headers should be included in the order:

  1. Core system headers (stdio.h, ctype.h, ...)
  2. Headers for non-core system components (X11, libraries).
  3. Headers for core systems of the package being compiled (grass/gis.h, grass/glocale.h, ...)
  4. Headers for the specific library/program being compiled (geodesic.h, ...)

Each class of header has an obligation to be compatible with those above it in the list, but not those below it.

  1. Always specify the return type for ALL functions including those that

return type "void", and insert return statements for any function which returns a value.

Also, use ANSI C prototypes to declare your functions. For module return values, see "Exit status" below.


    void G_something(void);
    int G_something_else(int, int);
    void G_something(void)
    	/* Snipped out code */
    int G_something_else(int x, int y)
    	/* Snipped out code */
	return 0;
  1. Module exit status is defined as EXIT_SUCCESS or EXIT_FAILURE

(declared in stdlib.h), e.g.

      if (G_parser (argc, argv))
          exit (EXIT_FAILURE);

      exit (EXIT_SUCCESS);
  1. Use fprintf() instead of printf()

For errors and warnings please use the G_fatal_error() and G_warning() functions. General messages for the user should use G_message() while debug messages should use G_debug() whenever

possible. There are two variants to G_message(): G_verbose_message() which will only display the message if in --verbose mode, and G_important_message() which will always show the message unless the module is running in --quiet mode. G_fatal_error() and G_warning() will always be displayed regardless of verbosity setting. Messages sent to any of these functions will be printed to stderr.

G_message() output is not expected to be sent to pipe or file.

Always use the gettext macros with _("") for user messages, example:

      G_fatal_error(_("Vector map <%s> not found"), name); 

It is suggested to add a comment line before translatable user message to give a hint to translators about meaning or use of cumbersome or obscure message. First word in the comment must be GTC - GRASS translation comment,


        /* GTC A name of a projection */
        G_message(_("State Plane"));

Any message with a noun in plural form has to pass _n() macro,

even if for the English language it is not required!

       G_message(_n("One map", "%d maps", number), number);

See [src:grass/trunk/locale/README] for details.

Pipe/file data output: For data output redirected to pipe or file, please use fprintf() and specify the stdout stream as follows:

      fprintf(stdout, ...);

      fflush(stdout) /* always required when using fprintf(stdout, ...). */
  1. Use the GRASS library function G_asprintf() instead of the standard C functions asprintf(), vsnprintf() and snprintf(). These functions are not portable or have other issues. Example:
        char *msg;
        G_asprintf(&msg, "%s", parameters);

Note that you should free memory when G_asprintf() is used.

  1. Use the following GRASS library functions instead of the standard C functions. The reason for this is that the following functions ensure good programming practice (e.g. always checking if memory was allocated)

and/or improves portability. PLEASE refer to the programmers manual for the proper use (e.g. determining if any casts are needed for arguments or return values) of these library functions. They may perform a task slightly different from their corresponding C library function, and thus, their use may not be the same.

    	G_malloc() instead of malloc()
	G_calloc() instead of calloc()
	G_realloc() instead of realloc()
	G_free() instead of free()
	G_getenv() instead of getenv()
	G_setenv() instead of setenv()
	G_unsetenv() instead of unsetenv()
	G_sleep() instead of sleep()

Could somebody please add others (please verify that they are useful and safe first)

  1. Use function names which fulfill the official GNU naming convention:

Instead of naming a function like: MyNewFunction() use underscores for seperation and lower case letters: my_new_function()`.

  1. Don't use the C++ comment style! This confuses several compilers.

Use instead:

       /* C-comments */

If you want to comment code portions, use

       #ifdef notdef 

This is safe comparing to nested /* comments */

Functions in the library must be documented in doxygen style to get them into the programmer's manual (generate with make pdfdocs or make htmldocs). See [src:grass/trunk/lib/gis/] for examples.

  1. PLEASE take the time to add comments throughout your code explaining what the code is doing. It will save a HUGE amount of time and frustration for other programmers that may have to change your code in the future.
  1. To promote a consistent coding style, please use the "indent" program on all new C modules using the following switches:
         $ indent -bad -bap -bbb -br -bli0 -bls -cli0 -ncs -fc1 -hnl -i4 \
          -nbbo -nbc -nbfda -nbfde -ncdb -ncdw -nce -nfca -npcs -nprs \
          -npsl -nsc -nsob -saf -sai -saw -sbi0 -ss -ts8 -ut main.c

Existing code should not be re-indented except in extreme cases, as this will make "diff" comparisons with older versions impossible. If indent is needed, do not check in any changes other than the indentation in the same commit! Do add the indent switches and any indent warning messages to the SVN log. Any change or fix mixed in with an indent is very hard to track

making it hard for others to follow the change or fix any new bugs. For your convenience use the src:grass/trunk/tools/ script.

  1. Platform dependent code:

Do not remove #ifdef __CYGWIN__ and/or #ifndef __CYGWIN__ lines and their encapsulated lines from source code (one example was that someone removed drand48 definition.)

  1. Suggested compiler flags:

We suggest to use very strict compiler flags to capture errors at the very beginning. Here our list of flags, please use them to configure you development version of GRASS:


       MYCFLAGS="-g -Wall -Werror-implicit-function-declaration -fno-common"
       MYCXXFLAGS="-g -Wall"
       CFLAGS="$MYCFLAGS" CXXFLAGS="$MYCXXFLAGS" ./configure ... 

MacOSX: [to be suggested]

MS-Windows: [to be suggested]

  1. Make sure a new line is at the end of each file and UNIX style newlines are used (\n).
  1. When writing Makefiles, use the current standard.

If you have to use commands, please check for:

            avoid     | use instead
    make target       | $(MAKE) target
    mkdir target      | $(MKDIR) target
    cp  (executable)  | $(INSTALL) -m 755 file target
    cp  (normal file) | $(INSTALL) -m 644 file target
    ar                | $(AR)

rm: be VERY careful with recursive remove. Also beware of removing $(FOO)* if $(FOO) has any chance of being empty.

Examples: see below examples or others

src:grass/trunk/raster/[[BR]] src:grass/trunk/vector/v.edit/Makefile

If you are unsure, please ask on the GRASS Developers list.

  1. Have a look at [src:grass/trunk/INSTALL]
  1. Have a function included in your module which writes to the history file of the map (e.g. command line, parameters etc.). See e.g. source:grass/raster/r.patch/main.c

(the same applies to vector and raster3d modules!)

  1. Standard parser options: use G_define_standard_option() whenever possible to define standard module command line options. This will save you time, create fewer bugs, and make things easier on the translators.

See source:grass/trunklib/gis/parser.c for details of the function definition.

  1. Add/update, if required the related GUI menus:
  1. For consistency, use README rather than README.txt for any README files.
  1. GRASS/Environment variables: If you add a new variable, please follow the naming convention. All variables are described in src:grass/trunk/lib/init/variables.html
  1. Be sure to develop on top of the LATEST GRASS code (which is in our SVN repository). You can re-check before submission with svn diff:

Be sure to create unified (diff -u) format. "Plain" diffs (the default format) are risky, because they will apply without warning to code which has been substantially changed; they are also harder to read than unified.

Such diffs should be made from the top-level directory, e.g. svn diff display/d.vect/main.c; that way, the diff will include the pathname rather than just an ambiguous main.c.

  1. Try to use module names which describe shortly the intended purpose of the module.

The first letters for module name should be:

	d. 	- display commands
	db. 	- database commands
	g. 	- general GIS management commands
	i. 	- imagery commands
	m.	- miscellaneous tool commands
	ps. 	- postscript commands
	r. 	- raster commands
	r3. 	- raster3D commands
	v. 	- vector commands

Some additional naming conventions

  • export modules: (type).out.(format) eg: r.out.arc, v.out.ascii
  • import module: (type).in.(format) eg:,
  • conversion modules: (type).to.(type) eg:,,

Avoid module names with more than two dots in the name. Example:

instead of use

  1. Use the grass test suite to test your modules.

You can easily write specific tests for your modules.

If your module is part of GRASS and you created some standard test cases, please contact the developers to add your tests to the default test suite. This will automatize complex test scenarios and assure to find bugs much faster, if changes were made to your modules or to the grass library.

Consider to subscribe to the GRASS Quality Assessment System to get immediate notification about the code quality:

  1. When submitting new files to the repository set SVN properties,

usually for directory

      svn:ignore : *.tmp.html

or e.g. for C-file

      svn:mime-type : text/x-csrc
      svn:keywords : Author Date Id
      svn:eol-style : native


To set a property:

      svn propset svn:keywords 'Author Date Id' <file>
      svn propset svn:mime-type text/x-sh

To edit the svn:ignore property using your default text editor:

      svn propedit svn:ignore <directory>

To set the svn:ignore property non-interactively, first create a

file containing the value:

      echo "*.tmp.html" > ignore.txt
      echo "*OBJ*" >> ignore.txt

then use:

      svn propset -F ignore.txt svn:ignore <directory>

List of mime-type:

      C++ files (.cpp): text/x-c++src
      C files (.c): text/x-csrc
      DTD files (.dtd): text/xml-dtd
      GIF files (.gif): image/gif
      Header files (.h): text/x-chdr
      HTML files (.html): text/html
      JPEG files (.jpg): image/jpeg
      Makefiles: text/x-makefile
      PNG files (.png): image/png
      Python files (.py): text/x-python
      Shell scripts (.sh): text/x-sh
      Text files (.txt): text/plain
      XML files (.xml): text/xml

(please update the list...)

For your convenience use the src:grass/trunk/tools/ script.

  1. Use doxygen style for source code documentation. It is required for GRASS libraries, but also recommended for GRASS modules.

Do not use structural command inside documentation block since it leads to some duplication of information (e.g. do not use \fn command in comment blocks). The exception is \file command for documenting a file, in this case structural command is required.

For files

       \file snap.c
       \brief Vector library - Clean vector map (snap lines)

       (C) 2001-2008 by the GRASS Development Team
       This program is free software under the GNU General Public
       License (>=v2).  Read the file COPYING that comes with GRASS
       for details.
       \author Radim Blazek

For functions

       \brief Snap lines in vector map to existing vertex in threshold

       For details see Vect_snap_lines_list()

       \param Map pointer to input vector map 
       \param type filter features of given type to be snap
       \param thresh threshold value for snapping
       \param[out] Err pointer to vector map where lines representing snap are written or NULL
       \param[out] msgout file pointer where messages will be written or NULL
       \return 1	   
  1. If you need to add support for a different library in the 'configure' script, you should first seek consent in the grass-dev mailing list (see below), then you need to expand '' and run subsequently autoconf-2.13 (later versions will not work) to re-generate 'configure'.
  1. Tell the other developers about the new code using the following e-mail:


To subscribe to this mailing list, see

  1. In case of questions feel free to contact the developers at the above

mailing list.


[please add further hints if required]

Your attention to detail is appreciated.