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GNU Info File | 1994-10-21 | 49KB | 937 lines

This is Info file standards.info, produced by Makeinfo-1.55 from the input file ./standards.texi. START-INFO-DIR-ENTRY * Standards: (standards). GNU coding standards. END-INFO-DIR-ENTRY GNU Coding Standards Copyright (C) 1992, 1993, 1994 Free Software Foundation Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Free Software Foundation. File: standards.info, Node: Top, Next: Reading Non-Free Code, Prev: (dir), Up: (dir) Version ******* Last updated 28 March 1994. * Menu: * Reading Non-Free Code:: Referring to Proprietary Programs * Contributions:: Accepting Contributions * Change Logs:: Recording Changes * Compatibility:: Compatibility with Other Implementations * Makefile Conventions:: Makefile Conventions * Configuration:: How Configuration Should Work * Source Language:: Using Languages Other Than C * Formatting:: Formatting Your Source Code * Comments:: Commenting Your Work * Syntactic Conventions:: Clean Use of C Constructs * Names:: Naming Variables and Functions * Using Extensions:: Using Non-standard Features * System Functions:: Portability and "standard" library functions * Semantics:: Program Behavior for All Programs * Errors:: Formatting Error Messages * Libraries:: Library Behavior * Portability:: Portability As It Applies to GNU * User Interfaces:: Standards for Command Line Interfaces * Documentation:: Documenting Programs * Releases:: Making Releases File: standards.info, Node: Reading Non-Free Code, Next: Contributions, Prev: Top, Up: Top Referring to Proprietary Programs ********************************* Don't in any circumstances refer to Unix source code for or during your work on GNU! (Or to any other proprietary programs.) If you have a vague recollection of the internals of a Unix program, this does not absolutely mean you can't write an imitation of it, but do try to organize the imitation internally along different lines, because this is likely to make the details of the Unix version irrelevant and dissimilar to your results. For example, Unix utilities were generally optimized to minimize memory use; if you go for speed instead, your program will be very different. You could keep the entire input file in core and scan it there instead of using stdio. Use a smarter algorithm discovered more recently than the Unix program. Eliminate use of temporary files. Do it in one pass instead of two (we did this in the assembler). Or, on the contrary, emphasize simplicity instead of speed. For some applications, the speed of today's computers makes simpler algorithms adequate. Or go for generality. For example, Unix programs often have static tables or fixed-size strings, which make for arbitrary limits; use dynamic allocation instead. Make sure your program handles NULs and other funny characters in the input files. Add a programming language for extensibility and write part of the program in that language. Or turn some parts of the program into independently usable libraries. Or use a simple garbage collector instead of tracking precisely when to free memory, or use a new GNU facility such as obstacks. File: standards.info, Node: Contributions, Next: Change Logs, Prev: Reading Non-Free Code, Up: Top Accepting Contributions *********************** If someone else sends you a piece of code to add to the program you are working on, we need legal papers to use it--the same sort of legal papers we will need to get from you. *Each* significant contributor to a program must sign some sort of legal papers in order for us to have clear title to the program. The main author alone is not enough. So, before adding in any contributions from other people, tell us so we can arrange to get the papers. Then wait until we tell you that we have received the signed papers, before you actually use the contribution. This applies both before you release the program and afterward. If you receive diffs to fix a bug, and they make significant change, we need legal papers for it. You don't need papers for changes of a few lines here or there, since they are not significant for copyright purposes. Also, you don't need papers if all you get from the suggestion is some ideas, not actual code which you use. For example, if you write a different solution to the problem, you don't need to get papers. I know this is frustrating; it's frustrating for us as well. But if you don't wait, you are going out on a limb--for example, what if the contributor's employer won't sign a disclaimer? You might have to take that code out again! The very worst thing is if you forget to tell us about the other contributor. We could be very embarrassed in court some day as a result. File: standards.info, Node: Change Logs, Next: Compatibility, Prev: Contributions, Up: Top Change Logs *********** Keep a change log for each directory, describing the changes made to source files in that directory. The purpose of this is so that people investigating bugs in the future will know about the changes that might have introduced the bug. Often a new bug can be found by looking at what was recently changed. More importantly, change logs can help eliminate conceptual inconsistencies between different parts of a program; they can give you a history of how the conflicting concepts arose. Use the Emacs command `M-x add-change' to start a new entry in the change log. An entry should have an asterisk, the name of the changed file, and then in parentheses the name of the changed functions, variables or whatever, followed by a colon. Then describe the changes you made to that function or variable. Separate unrelated entries with blank lines. When two entries represent parts of the same change, so that they work together, then don't put blank lines between them. Then you can omit the file name and the asterisk when successive entries are in the same file. Here are some examples: * register.el (insert-register): Return nil. (jump-to-register): Likewise. * sort.el (sort-subr): Return nil. * tex-mode.el (tex-bibtex-file, tex-file, tex-region): Restart the tex shell if process is gone or stopped. (tex-shell-running): New function. * expr.c (store_one_arg): Round size up for move_block_to_reg. (expand_call): Round up when emitting USE insns. * stmt.c (assign_parms): Round size up for move_block_from_reg. It's important to name the changed function or variable in full. Don't abbreviate them; don't combine them. Subsequent maintainers will often search for a function name to find all the change log entries that pertain to it; if you abbreviate the name, they won't find it when they search. For example, some people are tempted to abbreviate groups of function names by writing `* register.el ({insert,jump-to}-register)'; this is not a good idea, since searching for `jump-to-register' or `insert-register' would not find the entry. There's no need to describe the full purpose of the changes or how they work together. It is better to put such explanations in comments in the code. That's why just "New function" is enough; there is a comment with the function in the source to explain what it does. However, sometimes it is useful to write one line to describe the overall purpose of a large batch of changes. You can think of the change log as a conceptual "undo list" which explains how earlier versions were different from the current version. People can see the current version; they don't need the change log to tell them what is in it. What they want from a change log is a clear explanation of how the earlier version differed. When you change the calling sequence of a function in a simple fashion, and you change all the callers of the function, there is no need to make individual entries for all the callers. Just write in the entry for the function being called, "All callers changed." When you change just comments or doc strings, it is enough to write an entry for the file, without mentioning the functions. Write just, "Doc fix." There's no need to keep a change log for documentation files. This is because documentation is not susceptible to bugs that are hard to fix. Documentation does not consist of parts that must interact in a precisely engineered fashion; to correct an error, you need not know the history of the erroneous passage. File: standards.info, Node: Compatibility, Next: Makefile Conventions, Prev: Change Logs, Up: Top Compatibility with Other Implementations **************************************** With certain exceptions, utility programs and libraries for GNU should be upward compatible with those in Berkeley Unix, and upward compatible with ANSI C if ANSI C specifies their behavior, and upward compatible with POSIX if POSIX specifies their behavior. When these standards conflict, it is useful to offer compatibility modes for each of them. ANSI C and POSIX prohibit many kinds of extensions. Feel free to make the extensions anyway, and include a `--ansi' or `--compatible' option to turn them off. However, if the extension has a significant chance of breaking any real programs or scripts, then it is not really upward compatible. Try to redesign its interface. Many GNU programs suppress extensions that conflict with POSIX if the environment variable `POSIXLY_CORRECT' is defined (even if it is defined with a null value). Please make your program recognize this variable if appropriate. When a feature is used only by users (not by programs or command files), and it is done poorly in Unix, feel free to replace it completely with something totally different and better. (For example, vi is replaced with Emacs.) But it is nice to offer a compatible feature as well. (There is a free vi clone, so we offer it.) Additional useful features not in Berkeley Unix are welcome. Additional programs with no counterpart in Unix may be useful, but our first priority is usually to duplicate what Unix already has. File: standards.info, Node: Makefile Conventions, Next: Configuration, Prev: Compatibility, Up: Top Makefile Conventions ******************** This chapter describes conventions for writing the Makefiles for GNU programs. * Menu: * Makefile Basics:: * Utilities in Makefiles:: * Standard Targets:: * Command Variables:: * Directory Variables:: File: standards.info, Node: Makefile Basics, Next: Utilities in Makefiles, Up: Makefile Conventions General Conventions for Makefiles ================================= Every Makefile should contain this line: SHELL = /bin/sh to avoid trouble on systems where the `SHELL' variable might be inherited from the environment. (This is never a problem with GNU `make'.) Don't assume that `.' is in the path for command execution. When you need to run programs that are a part of your package during the make, please make sure that it uses `./' if the program is built as part of the make or `$(srcdir)/' if the file is an unchanging part of the source code. Without one of these prefixes, the current search path is used. The distinction between `./' and `$(srcdir)/' is important when using the `--srcdir' option to `configure'. A rule of the form: foo.1 : foo.man sedscript sed -e sedscript foo.man > foo.1 will fail when the current directory is not the source directory, because `foo.man' and `sedscript' are not in the current directory. When using GNU `make', relying on `VPATH' to find the source file will work in the case where there is a single dependency file, since the `make' automatic variable `$<' will represent the source file wherever it is. (Many versions of `make' set `$<' only in implicit rules.) A makefile target like foo.o : bar.c $(CC) -I. -I$(srcdir) $(CFLAGS) -c bar.c -o foo.o should instead be written as foo.o : bar.c $(CC) $(CFLAGS) $< -o $@ in order to allow `VPATH' to work correctly. When the target has multiple dependencies, using an explicit `$(srcdir)' is the easiest way to make the rule work well. For example, the target above for `foo.1' is best written as: foo.1 : foo.man sedscript sed -s $(srcdir)/sedscript $(srcdir)/foo.man > foo.1 File: standards.info, Node: Utilities in Makefiles, Next: Standard Targets, Prev: Makefile Basics, Up: Makefile Conventions Utilities in Makefiles ====================== Write the Makefile commands (and any shell scripts, such as `configure') to run in `sh', not in `csh'. Don't use any special features of `ksh' or `bash'. The `configure' script and the Makefile rules for building and installation should not use any utilities directly except these: cat cmp cp echo egrep expr grep ln mkdir mv pwd rm rmdir sed test touch Stick to the generally supported options for these programs. For example, don't use `mkdir -p', convenient as it may be, because most systems don't support it. The Makefile rules for building and installation can also use compilers and related programs, but should do so via `make' variables so that the user can substitute alternatives. Here are some of the programs we mean: ar bison cc flex install ld lex make makeinfo ranlib texi2dvi yacc When you use `ranlib', you should test whether it exists, and run it only if it exists, so that the distribution will work on systems that don't have `ranlib'. If you use symbolic links, you should implement a fallback for systems that don't have symbolic links. It is ok to use other utilities in Makefile portions (or scripts) intended only for particular systems where you know those utilities to exist. File: standards.info, Node: Standard Targets, Next: Command Variables, Prev: Utilities in Makefiles, Up: Makefile Conventions Standard Targets for Users ========================== All GNU programs should have the following targets in their Makefiles: `all' Compile the entire program. This should be the default target. This target need not rebuild any documentation files; Info files should normally be included in the distribution, and DVI files should be made only when explicitly asked for. `install' Compile the program and copy the executables, libraries, and so on to the file names where they should reside for actual use. If there is a simple test to verify that a program is properly installed, this target should run that test. The commands should create all the directories in which files are to be installed, if they don't already exist. This includes the directories specified as the values of the variables `prefix' and `exec_prefix', as well as all subdirectories that are needed. One way to do this is by means of an `installdirs' target as described below. Use `-' before any command for installing a man page, so that `make' will ignore any errors. This is in case there are systems that don't have the Unix man page documentation system installed. The way to install Info files is to copy them into `$(infodir)' with `$(INSTALL_DATA)' (*note Command Variables::.), and then run the `install-info' program if it is present. `install-info' is a script that edits the Info `dir' file to add or update the menu entry for the given Info file; it will be part of the Texinfo package. Here is a sample rule to install an Info file: $(infodir)/foo.info: foo.info # There may be a newer info file in . than in srcdir. -if test -f foo.info; then d=.; \ else d=$(srcdir); fi; \ $(INSTALL_DATA) $$d/foo.info $@; \ # Run install-info only if it exists. # Use `if' instead of just prepending `-' to the # line so we notice real errors from install-info. # We use `$(SHELL) -c' because some shells do not # fail gracefully when there is an unknown command. if $(SHELL) -c 'install-info --version' \ >/dev/null 2>&1; then \ install-info --infodir=$(infodir) $$d/foo.info; \ else true; fi `uninstall' Delete all the installed files that the `install' target would create (but not the noninstalled files such as `make all' would create). `clean' Delete all files from the current directory that are normally created by building the program. Don't delete the files that record the configuration. Also preserve files that could be made by building, but normally aren't because the distribution comes with them. Delete `.dvi' files here if they are not part of the distribution. `distclean' Delete all files from the current directory that are created by configuring or building the program. If you have unpacked the source and built the program without creating any other files, `make distclean' should leave only the files that were in the distribution. `mostlyclean' Like `clean', but may refrain from deleting a few files that people normally don't want to recompile. For example, the `mostlyclean' target for GCC does not delete `libgcc.a', because recompiling it is rarely necessary and takes a lot of time. `realclean' Delete everything from the current directory that can be reconstructed with this Makefile. This typically includes everything deleted by `distclean', plus more: C source files produced by Bison, tags tables, Info files, and so on. One exception, however: `make realclean' should not delete `configure' even if `configure' can be remade using a rule in the Makefile. More generally, `make realclean' should not delete anything that needs to exist in order to run `configure' and then begin to build the program. `TAGS' Update a tags table for this program. `info' Generate any Info files needed. The best way to write the rules is as follows: info: foo.info foo.info: foo.texi chap1.texi chap2.texi $(MAKEINFO) $(srcdir)/foo.texi You must define the variable `MAKEINFO' in the Makefile. It should run the `makeinfo' program, which is part of the Texinfo distribution. `dvi' Generate DVI files for all TeXinfo documentation. For example: dvi: foo.dvi foo.dvi: foo.texi chap1.texi chap2.texi $(TEXI2DVI) $(srcdir)/foo.texi You must define the variable `TEXI2DVI' in the Makefile. It should run the program `texi2dvi', which is part of the Texinfo distribution. Alternatively, write just the dependencies, and allow GNU Make to provide the command. `dist' Create a distribution tar file for this program. The tar file should be set up so that the file names in the tar file start with a subdirectory name which is the name of the package it is a distribution for. This name can include the version number. For example, the distribution tar file of GCC version 1.40 unpacks into a subdirectory named `gcc-1.40'. The easiest way to do this is to create a subdirectory appropriately named, use `ln' or `cp' to install the proper files in it, and then `tar' that subdirectory. The `dist' target should explicitly depend on all non-source files that are in the distribution, to make sure they are up to date in the distribution. *Note Making Releases: (standards)Releases. `check' Perform self-tests (if any). The user must build the program before running the tests, but need not install the program; you should write the self-tests so that they work when the program is built but not installed. The following targets are suggested as conventional names, for programs in which they are useful. `installcheck' Perform installation tests (if any). The user must build and install the program before running the tests. You should not assume that `$(bindir)' is in the search path. `installdirs' It's useful to add a target named `installdirs' to create the directories where files are installed, and their parent directories. There is a script called `mkinstalldirs' which is convenient for this; find it in the Texinfo package.You can use a rule like this: # Make sure all installation directories (e.g. $(bindir)) # actually exist by making them if necessary. installdirs: mkinstalldirs $(srcdir)/mkinstalldirs $(bindir) $(datadir) \ $(libdir) $(infodir) \ $(mandir) File: standards.info, Node: Command Variables, Next: Directory Variables, Prev: Standard Targets, Up: Makefile Conventions Variables for Specifying Commands ================================= Makefiles should provide variables for overriding certain commands, options, and so on. In particular, you should run most utility programs via variables. Thus, if you use Bison, have a variable named `BISON' whose default value is set with `BISON = bison', and refer to it with `$(BISON)' whenever you need to use Bison. File management utilities such as `ln', `rm', `mv', and so on, need not be referred to through variables in this way, since users don't need to replace them with other programs. Each program-name variable should come with an options variable that is used to supply options to the program. Append `FLAGS' to the program-name variable name to get the options variable name--for example, `BISONFLAGS'. (The name `CFLAGS' is an exception to this rule, but we keep it because it is standard.) Use `CPPFLAGS' in any compilation command that runs the preprocessor, and use `LDFLAGS' in any compilation command that does linking as well as in any direct use of `ld'. If there are C compiler options that *must* be used for proper compilation of certain files, do not include them in `CFLAGS'. Users expect to be able to specify `CFLAGS' freely themselves. Instead, arrange to pass the necessary options to the C compiler independently of `CFLAGS', by writing them explicitly in the compilation commands or by defining an implicit rule, like this: CFLAGS = -g ALL_CFLAGS = -I. $(CFLAGS) .c.o: $(CC) -c $(CPPFLAGS) $(ALL_CFLAGS) $< Do include the `-g' option in `CFLAGS', because that is not *required* for proper compilation. You can consider it a default that is only recommended. If the package is set up so that it is compiled with GCC by default, then you might as well include `-O' in the default value of `CFLAGS' as well. Put `CFLAGS' last in the compilation command, after other variables containing compiler options, so the user can use `CFLAGS' to override the others. Every Makefile should define the variable `INSTALL', which is the basic command for installing a file into the system. Every Makefile should also define the variables `INSTALL_PROGRAM' and `INSTALL_DATA'. (The default for each of these should be `$(INSTALL)'.) Then it should use those variables as the commands for actual installation, for executables and nonexecutables respectively. Use these variables as follows: $(INSTALL_PROGRAM) foo $(bindir)/foo $(INSTALL_DATA) libfoo.a $(libdir)/libfoo.a Always use a file name, not a directory name, as the second argument of the installation commands. Use a separate command for each file to be installed. File: standards.info, Node: Directory Variables, Prev: Command Variables, Up: Makefile Conventions Variables for Installation Directories ====================================== Installation directories should always be named by variables, so it is easy to install in a nonstandard place. The standard names for these variables are: `prefix' A prefix used in constructing the default values of the variables listed below. The default value of `prefix' should be `/usr/local' (at least for now). `exec_prefix' A prefix used in constructing the default values of some of the variables listed below. The default value of `exec_prefix' should be `$(prefix)'. Generally, `$(exec_prefix)' is used for directories that contain machine-specific files (such as executables and subroutine libraries), while `$(prefix)' is used directly for other directories. `bindir' The directory for installing executable programs that users can run. This should normally be `/usr/local/bin', but write it as `$(exec_prefix)/bin'. `libdir' The directory for installing executable files to be run by the program rather than by users. Object files and libraries of object code should also go in this directory. The idea is that this directory is used for files that pertain to a specific machine architecture, but need not be in the path for commands. The value of `libdir' should normally be `/usr/local/lib', but write it as `$(exec_prefix)/lib'. `datadir' The directory for installing read-only data files which the programs refer to while they run. This directory is used for files which are independent of the type of machine being used. This should normally be `/usr/local/lib', but write it as `$(prefix)/lib'. `statedir' The directory for installing data files which the programs modify while they run. These files should be independent of the type of machine being used, and it should be possible to share them among machines at a network installation. This should normally be `/usr/local/lib', but write it as `$(prefix)/lib'. `includedir' The directory for installing header files to be included by user programs with the C `#include' preprocessor directive. This should normally be `/usr/local/include', but write it as `$(prefix)/include'. Most compilers other than GCC do not look for header files in `/usr/local/include'. So installing the header files this way is only useful with GCC. Sometimes this is not a problem because some libraries are only really intended to work with GCC. But some libraries are intended to work with other compilers. They should install their header files in two places, one specified by `includedir' and one specified by `oldincludedir'. `oldincludedir' The directory for installing `#include' header files for use with compilers other than GCC. This should normally be `/usr/include'. The Makefile commands should check whether the value of `oldincludedir' is empty. If it is, they should not try to use it; they should cancel the second installation of the header files. A package should not replace an existing header in this directory unless the header came from the same package. Thus, if your Foo package provides a header file `foo.h', then it should install the header file in the `oldincludedir' directory if either (1) there is no `foo.h' there or (2) the `foo.h' that exists came from the Foo package. To tell whether `foo.h' came from the Foo package, put a magic string in the file--part of a comment--and grep for that string. `mandir' The directory for installing the man pages (if any) for this package. It should include the suffix for the proper section of the manual--usually `1' for a utility. It will normally be `/usr/local/man/man1', but you should write it as `$(prefix)/man/man1'. `man1dir' The directory for installing section 1 man pages. `man2dir' The directory for installing section 2 man pages. `...' Use these names instead of `mandir' if the package needs to install man pages in more than one section of the manual. *Don't make the primary documentation for any GNU software be a man page. Write a manual in Texinfo instead. Man pages are just for the sake of people running GNU software on Unix, which is a secondary application only.* `manext' The file name extension for the installed man page. This should contain a period followed by the appropriate digit; it should normally be `.1'. `man1ext' The file name extension for installed section 1 man pages. `man2ext' The file name extension for installed section 2 man pages. `...' Use these names instead of `manext' if the package needs to install man pages in more than one section of the manual. `infodir' The directory for installing the Info files for this package. By default, it should be `/usr/local/info', but it should be written as `$(prefix)/info'. `srcdir' The directory for the sources being compiled. The value of this variable is normally inserted by the `configure' shell script. For example: # Common prefix for installation directories. # NOTE: This directory must exist when you start the install. prefix = /usr/local exec_prefix = $(prefix) # Where to put the executable for the command `gcc'. bindir = $(exec_prefix)/bin # Where to put the directories used by the compiler. libdir = $(exec_prefix)/lib # Where to put the Info files. infodir = $(prefix)/info If your program installs a large number of files into one of the standard user-specified directories, it might be useful to group them into a subdirectory particular to that program. If you do this, you should write the `install' rule to create these subdirectories. Do not expect the user to include the subdirectory name in the value of any of the variables listed above. The idea of having a uniform set of variable names for installation directories is to enable the user to specify the exact same values for several different GNU packages. In order for this to be useful, all the packages must be designed so that they will work sensibly when the user does so. File: standards.info, Node: Configuration, Next: Source Language, Prev: Makefile Conventions, Up: Top How Configuration Should Work ***************************** Each GNU distribution should come with a shell script named `configure'. This script is given arguments which describe the kind of machine and system you want to compile the program for. The `configure' script must record the configuration options so that they affect compilation. One way to do this is to make a link from a standard name such as `config.h' to the proper configuration file for the chosen system. If you use this technique, the distribution should *not* contain a file named `config.h'. This is so that people won't be able to build the program without configuring it first. Another thing that `configure' can do is to edit the Makefile. If you do this, the distribution should *not* contain a file named `Makefile'. Instead, include a file `Makefile.in' which contains the input used for editing. Once again, this is so that people won't be able to build the program without configuring it first. If `configure' does write the `Makefile', then `Makefile' should have a target named `Makefile' which causes `configure' to be rerun, setting up the same configuration that was set up last time. The files that `configure' reads should be listed as dependencies of `Makefile'. All the files which are output from the `configure' script should have comments at the beginning explaining that they were generated automatically using `configure'. This is so that users won't think of trying to edit them by hand. The `configure' script should write a file named `config.status' which describes which configuration options were specified when the program was last configured. This file should be a shell script which, if run, will recreate the same configuration. The `configure' script should accept an option of the form `--srcdir=DIRNAME' to specify the directory where sources are found (if it is not the current directory). This makes it possible to build the program in a separate directory, so that the actual source directory is not modified. If the user does not specify `--srcdir', then `configure' should check both `.' and `..' to see if it can find the sources. If it finds the sources in one of these places, it should use them from there. Otherwise, it should report that it cannot find the sources, and should exit with nonzero status. Usually the easy way to support `--srcdir' is by editing a definition of `VPATH' into the Makefile. Some rules may need to refer explicitly to the specified source directory. To make this possible, `configure' can add to the Makefile a variable named `srcdir' whose value is precisely the specified directory. The `configure' script should also take an argument which specifies the type of system to build the program for. This argument should look like this: CPU-COMPANY-SYSTEM For example, a Sun 3 might be `m68k-sun-sunos4.1'. The `configure' script needs to be able to decode all plausible alternatives for how to describe a machine. Thus, `sun3-sunos4.1' would be a valid alias. So would `sun3-bsd4.2', since SunOS is basically BSD and no other BSD system is used on a Sun. For many programs, `vax-dec-ultrix' would be an alias for `vax-dec-bsd', simply because the differences between Ultrix and BSD are rarely noticeable, but a few programs might need to distinguish them. There is a shell script called `config.sub' that you can use as a subroutine to validate system types and canonicalize aliases. Other options are permitted to specify in more detail the software or hardware present on the machine, and include or exclude optional parts of the package: `--enable-FEATURE[=PARAMETER]' Configure the package to build and install an optional user-level facility called FEATURE. This allows users to choose which optional features to include. Giving an optional PARAMETER of `no' should omit FEATURE, if it is built by default. No `--enable' option should *ever* cause one feature to replace another. No `--enable' option should ever substitute one useful behavior for another useful behavior. The only proper use for `--enable' is for questions of whether to build part of the program or exclude it. `--with-PACKAGE' The package PACKAGE will be installed, so configure this package to work with PACKAGE. Possible values of PACKAGE include `x', `x-toolkit', `gnu-as' (or `gas'), `gnu-ld', `gnu-libc', and `gdb'. Do not use a `--with' option to specify the file name to use to find certain files. That is outside the scope of what `--with' options are for. `--nfp' The target machine has no floating point processor. `--gas' The target machine assembler is GAS, the GNU assembler. This is obsolete; users should use `--with-gnu-as' instead. `--x' The target machine has the X Window System installed. This is obsolete; users should use `--with-x' instead. All `configure' scripts should accept all of these "detail" options, whether or not they make any difference to the particular package at hand. In particular, they should accept any option that starts with `--with-' or `--enable-'. This is so users will be able to configure an entire GNU source tree at once with a single set of options. You will note that the categories `--with-' and `--enable-' are narrow: they *do not* provide a place for any sort of option you might think of. That is deliberate. We want to limit the possible configuration options in GNU software. We do not want GNU programs to have idiosyncratic configuration options. Packages that perform part of compilation may support cross-compilation. In such a case, the host and target machines for the program may be different. The `configure' script should normally treat the specified type of system as both the host and the target, thus producing a program which works for the same type of machine that it runs on. The way to build a cross-compiler, cross-assembler, or what have you, is to specify the option `--host=HOSTTYPE' when running `configure'. This specifies the host system without changing the type of target system. The syntax for HOSTTYPE is the same as described above. Bootstrapping a cross-compiler requires compiling it on a machine other than the host it will run on. Compilation packages accept a configuration option `--build=HOSTTYPE' for specifying the configuration on which you will compile them, in case that is different from the host. Programs for which cross-operation is not meaningful need not accept the `--host' option, because configuring an entire operating system for cross-operation is not a meaningful thing. Some programs have ways of configuring themselves automatically. If your program is set up to do this, your `configure' script can simply ignore most of its arguments. File: standards.info, Node: Source Language, Next: Formatting, Prev: Configuration, Up: Top Using Languages Other Than C **************************** Using a language other than C is like using a non-standard feature: it will cause trouble for users. Even if GCC supports the other language, users may find it inconvenient to have to install the compiler for that other language in order to build your program. So please write in C. There are three exceptions for this rule: * It is okay to use a special language if the same program contains an interpreter for that language. Thus, it is not a problem that GNU Emacs contains code written in Emacs Lisp, because it comes with a Lisp interpreter. * It is okay to use another language in a tool specifically intended for use with that language. This is okay because the only people who want to build the tool will be those who have installed the other language anyway. * If an application is not of extremely widespread interest, then perhaps it's not important if the application is inconvenient to install. File: standards.info, Node: Formatting, Next: Comments, Prev: Source Language, Up: Top Formatting Your Source Code *************************** It is important to put the open-brace that starts the body of a C function in column zero, and avoid putting any other open-brace or open-parenthesis or open-bracket in column zero. Several tools look for open-braces in column zero to find the beginnings of C functions. These tools will not work on code not formatted that way. It is also important for function definitions to start the name of the function in column zero. This helps people to search for function definitions, and may also help certain tools recognize them. Thus, the proper format is this: static char * concat (s1, s2) /* Name starts in column zero here */ char *s1, *s2; { /* Open brace in column zero here */ ... } or, if you want to use ANSI C, format the definition like this: static char * concat (char *s1, char *s2) { ... } In ANSI C, if the arguments don't fit nicely on one line, split it like this: int lots_of_args (int an_integer, long a_long, short a_short, double a_double, float a_float) ... For the body of the function, we prefer code formatted like this: if (x < foo (y, z)) haha = bar[4] + 5; else { while (z) { haha += foo (z, z); z--; } return ++x + bar (); } We find it easier to read a program when it has spaces before the open-parentheses and after the commas. Especially after the commas. When you split an expression into multiple lines, split it before an operator, not after one. Here is the right way: if (foo_this_is_long && bar > win (x, y, z) && remaining_condition) Try to avoid having two operators of different precedence at the same level of indentation. For example, don't write this: mode = (inmode[j] == VOIDmode || GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j]) ? outmode[j] : inmode[j]); Instead, use extra parentheses so that the indentation shows the nesting: mode = ((inmode[j] == VOIDmode || (GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j]))) ? outmode[j] : inmode[j]); Insert extra parentheses so that Emacs will indent the code properly. For example, the following indentation looks nice if you do it by hand, but Emacs would mess it up: v = rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000 + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000; But adding a set of parentheses solves the problem: v = (rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000 + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000); Format do-while statements like this: do { a = foo (a); } while (a > 0); Please use formfeed characters (control-L) to divide the program into pages at logical places (but not within a function). It does not matter just how long the pages are, since they do not have to fit on a printed page. The formfeeds should appear alone on lines by themselves. File: standards.info, Node: Comments, Next: Syntactic Conventions, Prev: Formatting, Up: Top Commenting Your Work ******************** Every program should start with a comment saying briefly what it is for. Example: `fmt - filter for simple filling of text'. Please put a comment on each function saying what the function does, what sorts of arguments it gets, and what the possible values of arguments mean and are used for. It is not necessary to duplicate in words the meaning of the C argument declarations, if a C type is being used in its customary fashion. If there is anything nonstandard about its use (such as an argument of type `char *' which is really the address of the second character of a string, not the first), or any possible values that would not work the way one would expect (such as, that strings containing newlines are not guaranteed to work), be sure to say so. Also explain the significance of the return value, if there is one. Please put two spaces after the end of a sentence in your comments, so that the Emacs sentence commands will work. Also, please write complete sentences and capitalize the first word. If a lower-case identifer comes at the beginning of a sentence, don't capitalize it! Changing the spelling makes it a different identifier. If you don't like starting a sentence with a lower case letter, write the sentence differently (e.g., "The identifier lower-case is ..."). The comment on a function is much clearer if you use the argument names to speak about the argument values. The variable name itself should be lower case, but write it in upper case when you are speaking about the value rather than the variable itself. Thus, "the inode number NODE_NUM" rather than "an inode". There is usually no purpose in restating the name of the function in the comment before it, because the reader can see that for himself. There might be an exception when the comment is so long that the function itself would be off the bottom of the screen. There should be a comment on each static variable as well, like this: /* Nonzero means truncate lines in the display; zero means continue them. */ int truncate_lines; Every `#endif' should have a comment, except in the case of short conditionals (just a few lines) that are not nested. The comment should state the condition of the conditional that is ending, *including its sense*. `#else' should have a comment describing the condition *and sense* of the code that follows. For example: #ifdef foo ... #else /* not foo */ ... #endif /* not foo */ but, by contrast, write the comments this way for a `#ifndef': #ifndef foo ... #else /* foo */ ... #endif /* foo */ File: standards.info, Node: Syntactic Conventions, Next: Names, Prev: Comments, Up: Top Clean Use of C Constructs ************************* Please explicitly declare all arguments to functions. Don't omit them just because they are `int's. Declarations of external functions and functions to appear later in the source file should all go in one place near the beginning of the file (somewhere before the first function definition in the file), or else should go in a header file. Don't put `extern' declarations inside functions. It used to be common practice to use the same local variables (with names like `tem') over and over for different values within one function. Instead of doing this, it is better declare a separate local variable for each distinct purpose, and give it a name which is meaningful. This not only makes programs easier to understand, it also facilitates optimization by good compilers. You can also move the declaration of each local variable into the smallest scope that includes all its uses. This makes the program even cleaner. Don't use local variables or parameters that shadow global identifiers. Don't declare multiple variables in one declaration that spans lines. Start a new declaration on each line, instead. For example, instead of this: int foo, bar; write either this: int foo, bar; or this: int foo; int bar; (If they are global variables, each should have a comment preceding it anyway.) When you have an `if'-`else' statement nested in another `if' statement, always put braces around the `if'-`else'. Thus, never write like this: if (foo) if (bar) win (); else lose (); always like this: if (foo) { if (bar) win (); else lose (); } If you have an `if' statement nested inside of an `else' statement, either write `else if' on one line, like this, if (foo) ... else if (bar) ... with its `then'-part indented like the preceding `then'-part, or write the nested `if' within braces like this: if (foo) ... else { if (bar) ... } Don't declare both a structure tag and variables or typedefs in the same declaration. Instead, declare the structure tag separately and then use it to declare the variables or typedefs. Try to avoid assignments inside `if'-conditions. For example, don't write this: if ((foo = (char *) malloc (sizeof *foo)) == 0) fatal ("virtual memory exhausted"); instead, write this: foo = (char *) malloc (sizeof *foo); if (foo == 0) fatal ("virtual memory exhausted"); Don't make the program ugly to placate `lint'. Please don't insert any casts to `void'. Zero without a cast is perfectly fine as a null pointer constant. File: standards.info, Node: Names, Next: Using Extensions, Prev: Syntactic Conventions, Up: Top Naming Variables and Functions ****************************** Please use underscores to separate words in a name, so that the Emacs word commands can be useful within them. Stick to lower case; reserve upper case for macros and `enum' constants, and for name-prefixes that follow a uniform convention. For example, you should use names like `ignore_space_change_flag'; don't use names like `iCantReadThis'. Variables that indicate whether command-line options have been specified should be named after the meaning of the option, not after the option-letter. A comment should state both the exact meaning of the option and its letter. For example, /* Ignore changes in horizontal whitespace (-b). */ int ignore_space_change_flag; When you want to define names with constant integer values, use `enum' rather than `#define'. GDB knows about enumeration constants. Use file names of 14 characters or less, to avoid creating gratuitous problems on System V. You can use the program `doschk' to test for this. `doschk' also tests for potential name conflicts if the files were loaded onto an MS-DOS file system--something you may or may not care about.