(M-40132'): Unify GT-53970.

[chise/xemacs-chise.git-] / info / standards.info-2

This is ../info/standards.info, produced by makeinfo version 4.0 from
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,
1997, 1998, 1999 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.

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File: standards.info,  Node: Comments,  Next: Syntactic Conventions,  Prev: Formatting,  Up: Writing C

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 write the comments in a GNU program in English, because
English is the one language that nearly all programmers in all
countries can read.  If you do not write English well, please write
comments in English as well as you can, then ask other people to help
rewrite them.  If you can't write comments in English, please find
someone to work with you and translate your comments into English.

   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
identifier 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 */
     #ifdef foo
       ...
     #endif /* foo */

but, by contrast, write the comments this way for a `#ifndef':

     #ifndef foo
       ...
     #else /* foo */
       ...
     #endif /* foo */
     #ifndef foo
       ...
     #endif /* not foo */

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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.

\1f
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.

   Try to limit your use of abbreviations in symbol names.  It is ok to
make a few abbreviations, explain what they mean, and then use them
frequently, but don't use lots of obscure abbreviations.

   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.

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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 often a lot of work.  When
that is the case, it is better to spend your time adding features that
will be useful on GNU and GNU/Linux, rather than on supporting other
incompatible systems.

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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;
          char *a1, *a2, *a3;
     {
       fprintf (stderr, "error: ");
       fprintf (stderr, s, a1, a2, a3);
     }

In practice, this works on all machines, since a pointer is generally
the widest possible kind of argument, 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.  Outside of special situations, such casts greatly 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 it, but you'll have to make explicit provisions to
handle different word sizes.

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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.

\1f
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 be 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");

\1f
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.

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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.
* License for Manuals::         Writing the distribution terms for a manual.
* 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.

\1f
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.  This makes it possible to
produce a good quality formatted book, using TeX, and to generate an
Info file.  It is also possible to generate HTML output from Texinfo
source.  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.  The
Bison manual is a good example of this--please take a look at it to see
what we mean.

   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 include an email address in the manual for where to report
bugs _in the manual_.

   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 directory 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.

\1f
File: standards.info,  Node: Manual Structure Details,  Next: License for Manuals,  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 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.

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File: standards.info,  Node: License for Manuals,  Next: NEWS File,  Prev: Manual Structure Details,  Up: Documentation

License for Manuals
===================

   If the manual contains a copy of the GNU GPL or GNU LGPL, or if it
contains chapters that make political or personal statements, please
copy the distribution terms of the GNU Emacs Manual, and adapt it by
modifying appropriately the list of special chapters that may not be
modified or deleted.

   If the manual does not contain any such chapters, then imitate the
simpler distribution terms of the Texinfo manual.

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File: standards.info,  Node: NEWS File,  Next: Change Logs,  Prev: License for Manuals,  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.

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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::

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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 using `rcs2log'; in Emacs, the
command `C-x v a' (`vc-update-change-log') does the job.

   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.

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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.

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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.

\1f
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.

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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.

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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.

\1f
File: standards.info,  Node: Managing Releases,  Next: References,  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

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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 `gnu-as' (or `gas'), `gnu-ld',
     `gnu-libc', `gdb', `x', and `x-toolkit'.

     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.

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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.  Using Automake will help you write a Makefile that follows
these conventions.

* 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.

\1f
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'.