This is Info file standards.info, produced by Makeinfo-1.64 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, 1995, 1996 Free Software Foundation, Inc. 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: Syntactic Conventions, Next: Names, Prev: Comments, Up: Writing C 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, except when calling a varargs function.  File: standards.info, Node: Names, Next: System Portability, Prev: Syntactic Conventions, Up: Writing C Naming Variables and Functions ============================== The names of global variables and functions in a program serve as comments of a sort. So don't choose terse names--instead, look for names that give useful information about the meaning of the variable or function. In a GNU program, names should be English, like other comments. Local variable names can be shorter, because they are used only within one context, where (presumably) comments explain their purpose. 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 older System V systems. 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.  File: standards.info, Node: System Portability, Next: CPU Portability, Prev: Names, Up: Writing C Portability between System Types ================================ In the Unix world, "portability" refers to porting to different Unix versions. For a GNU program, this kind of portability is desirable, but not paramount. The primary purpose of GNU software is to run on top of the GNU kernel, compiled with the GNU C compiler, on various types of CPU. The amount and kinds of variation among GNU systems on different CPUs will be comparable to the variation among Linux-based GNU systems or among BSD systems today. So the kinds of portability that are absolutely necessary are quite limited. But many users do run GNU software on non-GNU Unix or Unix-like systems. So supporting a variety of Unix-like systems is desirable, although not paramount. The easiest way to achieve portability to most Unix-like systems is to use Autoconf. It's unlikely that your program needs to know more information about the host platform than Autoconf can provide, simply because most of the programs that need such knowledge have already been written. Avoid using the format of semi-internal data bases (e.g., directories) when there is a higher-level alternative (`readdir'). As for systems that are not like Unix, such as MSDOS, Windows, the Macintosh, VMS, and MVS, supporting them is usually so much work that it is better if you don't. The planned GNU kernel is not finished yet, but you can tell which facilities it will provide by looking at the GNU C Library Manual. The GNU kernel is based on Mach, so the features of Mach will also be available. However, if you use Mach features, you'll probably have trouble debugging your program today.  File: standards.info, Node: CPU Portability, Next: System Functions, Prev: System Portability, Up: Writing C Portability between CPUs ======================== Even GNU systems will differ because of differences among CPU types--for example, difference in byte ordering and alignment requirements. It is absolutely essential to handle these differences. However, don't make any effort to cater to the possibility that an `int' will be less than 32 bits. We don't support 16-bit machines in GNU. Don't assume that the address of an `int' object is also the address of its least-significant byte. This is false on big-endian machines. Thus, don't make the following mistake: int c; ... while ((c = getchar()) != EOF) write(file_descriptor, &c, 1); When calling functions, you need not worry about the difference between pointers of various types, or between pointers and integers. On most machines, there's no difference anyway. As for the few machines where there is a difference, all of them support ANSI C, so you can use prototypes (conditionalized to be active only in ANSI C) to make the code work on those systems. In certain cases, it is ok to pass integer and pointer arguments indiscriminately to the same function, and use no prototype on any system. For example, many GNU programs have error-reporting functions that pass their arguments along to `printf' and friends: error (s, a1, a2, a3) char *s; int a1, a2, a3; { fprintf (stderr, "error: "); fprintf (stderr, s, a1, a2, a3); } In practice, this works on all machines, and it is much simpler than any "correct" alternative. Be sure *not* to use a prototype for such functions. However, avoid casting pointers to integers unless you really need to. These assumptions really reduce portability, and in most programs they are easy to avoid. In the cases where casting pointers to integers is essential--such as, a Lisp interpreter which stores type information as well as an address in one word--it is ok to do so, but you'll have to make explicit provisions to handle different word sizes.  File: standards.info, Node: System Functions, Next: Internationalization, Prev: CPU Portability, Up: Writing C Calling System Functions ======================== C implementations differ substantially. ANSI C reduces but does not eliminate the incompatibilities; meanwhile, many users wish to compile GNU software with pre-ANSI compilers. This chapter gives recommendations for how to use the more or less standard C library functions to avoid unnecessary loss of portability. * Don't use the value of `sprintf'. It returns the number of characters written on some systems, but not on all systems. * `main' should be declared to return type `int'. It should terminate either by calling `exit' or by returning the integer status code; make sure it cannot ever return an undefined value. * Don't declare system functions explicitly. Almost any declaration for a system function is wrong on some system. To minimize conflicts, leave it to the system header files to declare system functions. If the headers don't declare a function, let it remain undeclared. While it may seem unclean to use a function without declaring it, in practice this works fine for most system library functions on the systems where this really happens; thus, the disadvantage is only theoretical. By contrast, actual declarations have frequently caused actual conflicts. * If you must declare a system function, don't specify the argument types. Use an old-style declaration, not an ANSI prototype. The more you specify about the function, the more likely a conflict. * In particular, don't unconditionally declare `malloc' or `realloc'. Most GNU programs use those functions just once, in functions conventionally named `xmalloc' and `xrealloc'. These functions call `malloc' and `realloc', respectively, and check the results. Because `xmalloc' and `xrealloc' are defined in your program, you can declare them in other files without any risk of type conflict. On most systems, `int' is the same length as a pointer; thus, the calls to `malloc' and `realloc' work fine. For the few exceptional systems (mostly 64-bit machines), you can use *conditionalized* declarations of `malloc' and `realloc'--or put these declarations in configuration files specific to those systems. * The string functions require special treatment. Some Unix systems have a header file `string.h'; others have `strings.h'. Neither file name is portable. There are two things you can do: use Autoconf to figure out which file to include, or don't include either file. * If you don't include either strings file, you can't get declarations for the string functions from the header file in the usual way. That causes less of a problem than you might think. The newer ANSI string functions should be avoided anyway because many systems still don't support them. The string functions you can use are these: strcpy strncpy strcat strncat strlen strcmp strncmp strchr strrchr The copy and concatenate functions work fine without a declaration as long as you don't use their values. Using their values without a declaration fails on systems where the width of a pointer differs from the width of `int', and perhaps in other cases. It is trivial to avoid using their values, so do that. The compare functions and `strlen' work fine without a declaration on most systems, possibly all the ones that GNU software runs on. You may find it necessary to declare them *conditionally* on a few systems. The search functions must be declared to return `char *'. Luckily, there is no variation in the data type they return. But there is variation in their names. Some systems give these functions the names `index' and `rindex'; other systems use the names `strchr' and `strrchr'. Some systems support both pairs of names, but neither pair works on all systems. You should pick a single pair of names and use it throughout your program. (Nowadays, it is better to choose `strchr' and `strrchr' for new programs, since those are the standard ANSI names.) Declare both of those names as functions returning `char *'. On systems which don't support those names, define them as macros in terms of the other pair. For example, here is what to put at the beginning of your file (or in a header) if you want to use the names `strchr' and `strrchr' throughout: #ifndef HAVE_STRCHR #define strchr index #endif #ifndef HAVE_STRRCHR #define strrchr rindex #endif char *strchr (); char *strrchr (); Here we assume that `HAVE_STRCHR' and `HAVE_STRRCHR' are macros defined in systems where the corresponding functions exist. One way to get them properly defined is to use Autoconf.  File: standards.info, Node: Internationalization, Next: Mmap, Prev: System Functions, Up: Writing C Internationalization ==================== GNU has a library called GNU gettext that makes it easy to translate the messages in a program into various languages. You should use this library in every program. Use English for the messages as they appear in the program, and let gettext provide the way to translate them into other languages. Using GNU gettext involves putting a call to the `gettext' macro around each string that might need translation--like this: printf (gettext ("Processing file `%s'...")); This permits GNU gettext to replace the string `"Processing file `%s'..."' with a translated version. Once a program uses gettext, please make a point of writing calls to `gettext' when you add new strings that call for translation. Using GNU gettext in a package involves specifying a "text domain name" for the package. The text domain name is used to separate the translations for this package from the translations for other packages. Normally, the text domain name should be the same as the name of the package--for example, `fileutils' for the GNU file utilities. To enable gettext to work well, avoid writing code that makes assumptions about the structure of words or sentences. When you want the precise text of a sentence to vary depending on the data, use two or more alternative string constants each containing a complete sentences, rather than inserting conditionalized words or phrases into a single sentence framework. Here is an example of what not to do: printf ("%d file%s processed", nfiles, nfiles != 1 ? "s" : ""); The problem with that example is that it assumes that plurals are made by adding `s'. If you apply gettext to the format string, like this, printf (gettext ("%d file%s processed"), nfiles, nfiles != 1 ? "s" : ""); the message can use different words, but it will still be forced to use `s' for the plural. Here is a better way: printf ((nfiles != 1 ? "%d files processed" : "%d file processed"), nfiles); This way, you can apply gettext to each of the two strings independently: printf ((nfiles != 1 ? gettext ("%d files processed") : gettext ("%d file processed")), nfiles); This can any method of forming the plural of the word for "file", and also handles languages that require agreement in the word for "processed". A similar problem appears at the level of sentence structure with this code: printf ("# Implicit rule search has%s been done.\n", f->tried_implicit ? "" : " not"); Adding `gettext' calls to this code cannot give correct results for all languages, because negation in some languages requires adding words at more than one place in the sentence. By contrast, adding `gettext' calls does the job straightfowardly if the code starts out like this: printf (f->tried_implicit ? "# Implicit rule search has been done.\n", : "# Implicit rule search has not been done.\n");  File: standards.info, Node: Mmap, Prev: Internationalization, Up: Writing C Mmap ==== Don't assume that `mmap' either works on all files or fails for all files. It may work on some files and fail on others. The proper way to use `mmap' is to try it on the specific file for which you want to use it--and if `mmap' doesn't work, fall back on doing the job in another way using `read' and `write'. The reason this precaution is needed is that the GNU kernel (the HURD) provides a user-extensible file system, in which there can be many different kinds of "ordinary files." Many of them support `mmap', but some do not. It is important to make programs handle all these kinds of files.  File: standards.info, Node: Documentation, Next: Managing Releases, Prev: Writing C, Up: Top Documenting Programs ******************** * Menu: * GNU Manuals:: Writing proper manuals. * Manual Structure Details:: Specific structure conventions. * NEWS File:: NEWS files supplement manuals. * Change Logs:: Recording Changes * Man Pages:: Man pages are secondary. * Reading other Manuals:: How far you can go in learning from other manuals.  File: standards.info, Node: GNU Manuals, Next: Manual Structure Details, Up: Documentation GNU Manuals =========== The preferred way to document part of the GNU system is to write a manual in the Texinfo formatting language. See the Texinfo manual, either the hardcopy, or the on-line version available through `info' or the Emacs Info subsystem (`C-h i'). Programmers often find it most natural to structure the documentation following the structure of the implementation, which they know. But this structure is not necessarily good for explaining how to use the program; it may be irrelevant and confusing for a user. At every level, from the sentences in a paragraph to the grouping of topics into separate manuals, the right way to structure documentation is according to the concepts and questions that a user will have in mind when reading it. Sometimes this structure of ideas matches the structure of the implementation of the software being documented--but often they are different. Often the most important part of learning to write good documentation is learning to notice when you are structuring the documentation like the implementation, and think about better alternatives. For example, each program in the GNU system probably ought to be documented in one manual; but this does not mean each program should have its own manual. That would be following the structure of the implementation, rather than the structure that helps the user understand. Instead, each manual should cover a coherent *topic*. For example, instead of a manual for `diff' and a manual for `diff3', we have one manual for "comparison of files" which covers both of those programs, as well as `cmp'. By documenting these programs together, we can make the whole subject clearer. The manual which discusses a program should document all of the program's command-line options and all of its commands. It should give examples of their use. But don't organize the manual as a list of features. Instead, organize it logically, by subtopics. Address the questions that a user will ask when thinking about the job that the program does. In general, a GNU manual should serve both as tutorial and reference. It should be set up for convenient access to each topic through Info, and for reading straight through (appendixes aside). A GNU manual should give a good introduction to a beginner reading through from the start, and should also provide all the details that hackers want. That is not as hard as it first sounds. Arrange each chapter as a logical breakdown of its topic, but order the sections, and write their text, so that reading the chapter straight through makes sense. Do likewise when structuring the book into chapters, and when structuring a section into paragraphs. The watchword is, *at each point, address the most fundamental and important issue raised by the preceding text.* If necessary, add extra chapters at the beginning of the manual which are purely tutorial and cover the basics of the subject. These provide the framework for a beginner to understand the rest of the manual. The Bison manual provides a good example of how to do this. Don't use Unix man pages as a model for how to write GNU documentation; most of them are terse, badly structured, and give inadequate explanation of the underlying concepts. (There are, of course exceptions.) Also Unix man pages use a particular format which is different from what we use in GNU manuals. Please do not use the term "pathname" that is used in Unix documentation; use "file name" (two words) instead. We use the term "path" only for search paths, which are lists of file names. Please do not use the term "illegal" to refer to erroneous input to a computer program. Please use "invalid" for this, and reserve the term "illegal" for violations of law.  File: standards.info, Node: Manual Structure Details, Next: NEWS File, Prev: GNU Manuals, Up: Documentation Manual Structure Details ======================== The title page of the manual should state the version of the programs or packages documented in the manual. The Top node of the manual should also contain this information. If the manual is changing more frequently than or independent of the program, also state a version number for the manual in both of these places. Each program documented in the manual should should have a node named `PROGRAM Invocation' or `Invoking PROGRAM'. This node (together with its subnodes, if any) should describe the program's command line arguments and how to run it (the sort of information people would look in a man page for). Start with an `@example' containing a template for all the options and arguments that the program uses. Alternatively, put a menu item in some menu whose item name fits one of the above patterns. This identifies the node which that item points to as the node for this purpose, regardless of the node's actual name. There will be automatic features for specifying a program name and quickly reading just this part of its manual. If one manual describes several programs, it should have such a node for each program described.  File: standards.info, Node: NEWS File, Next: Change Logs, Prev: Manual Structure Details, Up: Documentation The NEWS File ============= In addition to its manual, the package should have a file named `NEWS' which contains a list of user-visible changes worth mentioning. In each new release, add items to the front of the file and identify the version they pertain to. Don't discard old items; leave them in the file after the newer items. This way, a user upgrading from any previous version can see what is new. If the `NEWS' file gets very long, move some of the older items into a file named `ONEWS' and put a note at the end referring the user to that file.  File: standards.info, Node: Change Logs, Next: Man Pages, Prev: NEWS File, Up: Documentation Change Logs =========== Keep a change log to describe all the changes made to program source files. 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 you eliminate conceptual inconsistencies between different parts of a program, by giving you a history of how the conflicting concepts arose and who they came from. * Menu: * Change Log Concepts:: * Style of Change Logs:: * Simple Changes:: * Conditional Changes::  File: standards.info, Node: Change Log Concepts, Next: Style of Change Logs, Up: Change Logs Change Log Concepts ------------------- 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. The change log file is normally called `ChangeLog' and covers an entire directory. Each directory can have its own change log, or a directory can use the change log of its parent directory-it's up to you. Another alternative is to record change log information with a version control system such as RCS or CVS. This can be converted automatically to a `ChangeLog' file. There's no need to describe the full purpose of the changes or how they work together. If you think that a change calls for explanation, you're probably right. Please do explain it--but please put the explanation in comments in the code, where people will see it whenever they see the code. For example, "New function" is enough for the change log when you add a function, because there should be a comment before the function definition to explain what it does. However, sometimes it is useful to write one line to describe the overall purpose of a batch of changes. The easiest way to add an entry to `ChangeLog' is with the Emacs command `M-x add-change-log-entry'. 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.  File: standards.info, Node: Style of Change Logs, Next: Simple Changes, Prev: Change Log Concepts, Up: Change Logs Style of Change Logs -------------------- Here are some examples of change log entries: * 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 function or variable names, and 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 that entry. Separate unrelated change log 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.  File: standards.info, Node: Simple Changes, Next: Conditional Changes, Prev: Style of Change Logs, Up: Change Logs Simple Changes -------------- Certain simple kinds of changes don't need much detail in the change log. 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 that you changed. Just write in the entry for the function being called, "All callers changed." * keyboard.c (Fcommand_execute): New arg SPECIAL. 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. Just "Doc fixes" is enough for the change log. There's no need to make change log entries 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; it is enough to compare what the documentation says with the way the program actually works.  File: standards.info, Node: Conditional Changes, Prev: Simple Changes, Up: Change Logs Conditional Changes ------------------- C programs often contain compile-time `#if' conditionals. Many changes are conditional; sometimes you add a new definition which is entirely contained in a conditional. It is very useful to indicate in the change log the conditions for which the change applies. Our convention for indicating conditional changes is to use square brackets around the name of the condition. Here is a simple example, describing a change which is conditional but does not have a function or entity name associated with it: * xterm.c [SOLARIS2]: Include string.h. Here is an entry describing a new definition which is entirely conditional. This new definition for the macro `FRAME_WINDOW_P' is used only when `HAVE_X_WINDOWS' is defined: * frame.h [HAVE_X_WINDOWS] (FRAME_WINDOW_P): Macro defined. Here is an entry for a change within the function `init_display', whose definition as a whole is unconditional, but the changes themselves are contained in a `#ifdef HAVE_LIBNCURSES' conditional: * dispnew.c (init_display) [HAVE_LIBNCURSES]: If X, call tgetent. Here is an entry for a change that takes affect only when a certain macro is *not* defined: (gethostname) [!HAVE_SOCKETS]: Replace with winsock version.  File: standards.info, Node: Man Pages, Next: Reading other Manuals, Prev: Change Logs, Up: Documentation Man Pages ========= In the GNU project, man pages are secondary. It is not necessary or expected for every GNU program to have a man page, but some of them do. It's your choice whether to include a man page in your program. When you make this decision, consider that supporting a man page requires continual effort each time the program is changed. The time you spend on the man page is time taken away from more useful work. For a simple program which changes little, updating the man page may be a small job. Then there is little reason not to include a man page, if you have one. For a large program that changes a great deal, updating a man page may be a substantial burden. If a user offers to donate a man page, you may find this gift costly to accept. It may be better to refuse the man page unless the same person agrees to take full responsibility for maintaining it--so that you can wash your hands of it entirely. If this volunteer later ceases to do the job, then don't feel obliged to pick it up yourself; it may be better to withdraw the man page from the distribution until someone else agrees to update it. When a program changes only a little, you may feel that the discrepancies are small enough that the man page remains useful without updating. If so, put a prominent note near the beginning of the man page explaining that you don't maintain it and that the Texinfo manual is more authoritative. The note should say how to access the Texinfo documentation.  File: standards.info, Node: Reading other Manuals, Prev: Man Pages, Up: Documentation Reading other Manuals ===================== There may be non-free books or documentation files that describe the program you are documenting. It is ok to use these documents for reference, just as the author of a new algebra textbook can read other books on algebra. A large portion of any non-fiction book consists of facts, in this case facts about how a certain program works, and these facts are necessarily the same for everyone who writes about the subject. But be careful not to copy your outline structure, wording, tables or examples from preexisting non-free documentation. Copying from free documentation may be ok; please check with the FSF about the individual case.  File: standards.info, Node: Managing Releases, Prev: Documentation, Up: Top The Release Process ******************* Making a release is more than just bundling up your source files in a tar file and putting it up for FTP. You should set up your software so that it can be configured to run on a variety of systems. Your Makefile should conform to the GNU standards described below, and your directory layout should also conform to the standards discussed below. Doing so makes it easy to include your package into the larger framework of all GNU software. * Menu: * Configuration:: How Configuration Should Work * Makefile Conventions:: Makefile Conventions * Releases:: Making Releases  File: standards.info, Node: Configuration, Next: Makefile Conventions, Up: Managing Releases 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, it should 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. 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 the compilation process 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: Makefile Conventions, Next: Releases, Prev: Configuration, Up: Managing Releases Makefile Conventions ==================== This node describes conventions for writing the Makefiles for GNU programs. * Menu: * Makefile Basics:: General Conventions for Makefiles * Utilities in Makefiles:: Utilities in Makefiles * Command Variables:: Variables for Specifying Commands * Directory Variables:: Variables for Installation Directories * Standard Targets:: Standard Targets for Users * Install Command Categories:: Three categories of commands in the `install' rule: normal, pre-install and post-install.  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'.) Different `make' programs have incompatible suffix lists and implicit rules, and this sometimes creates confusion or misbehavior. So it is a good idea to set the suffix list explicitly using only the suffixes you need in the particular Makefile, like this: .SUFFIXES: .SUFFIXES: .c .o The first line clears out the suffix list, the second introduces all suffixes which may be subject to implicit rules in this Makefile. 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 `$(srcdir)/' if the file is an unchanging part of the source code. Without one of these prefixes, the current search path is used. The distinction between `./' (the "build directory") and `$(srcdir)/' (the "source directory") is important because users can build in a separate directory 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 build directory is not the source directory, because `foo.man' and `sedscript' are in the the source 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 $(CC) -I. -I$(srcdir) $(CFLAGS) -c $< -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 -e $(srcdir)/sedscript $(srcdir)/foo.man > $@ GNU distributions usually contain some files which are not source files--for example, Info files, and the output from Autoconf, Automake, Bison or Flex. Since these files normally appear in the source directory, they should always appear in the source directory, not in the build directory. So Makefile rules to update them should put the updated files in the source directory. However, if a file does not appear in the distribution, then the Makefile should not put it in the source directory, because building a program in ordinary circumstances should not modify the source directory in any way. Try to make the build and installation targets, at least (and all their subtargets) work correctly with a parallel `make'.  File: standards.info, Node: Utilities in Makefiles, Next: Command Variables, 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 diff echo egrep expr false grep install-info ln ls mkdir mv pwd rm rmdir sed sleep sort tar test touch true The compression program `gzip' can be used in the `dist' rule. 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. It is a good idea to avoid creating symbolic links in makefiles, since a few systems don't support them. 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 ldconfig lex make makeinfo ranlib texi2dvi yacc Use the following `make' variables to run those programs: $(AR) $(BISON) $(CC) $(FLEX) $(INSTALL) $(LD) $(LDCONFIG) $(LEX) $(MAKE) $(MAKEINFO) $(RANLIB) $(TEXI2DVI) $(YACC) When you use `ranlib' or `ldconfig', you should make sure nothing bad happens if the system does not have the program in question. Arrange to ignore an error from that command, and print a message before the command to tell the user that failure of this command does not mean a problem. (The Autoconf `AC_PROG_RANLIB' macro can help with this.) If you use symbolic links, you should implement a fallback for systems that don't have symbolic links. Additional utilities that can be used via Make variables are: chgrp chmod chown mknod It is ok to use other utilities in Makefile portions (or scripts) intended only for particular systems where you know those utilities exist.  File: standards.info, Node: Command Variables, Next: Directory Variables, Prev: Utilities in Makefiles, Up: Makefile Conventions Variables for Specifying Commands --------------------------------- Makefiles should provide variables for overriding certain commands, options, and so on. In particular, you should run most utility programs via variables. Thus, if you use Bison, have a variable named `BISON' whose default value is set with `BISON = bison', and refer to it with `$(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.