hda000000085.bin

em off.  However, if the extension has
a significant chance of breaking any real programs or scripts, then it
is not really upward compatible.  So you should try to redesign its
interface to make it upward compatible.

   Many GNU programs suppress extensions that conflict with POSIX if the
environment variable `POSIXLY_CORRECT' is defined (even if it is
defined with a null value).  Please make your program recognize this
variable if appropriate.

   When a feature is used only by users (not by programs or command
files), and it is done poorly in Unix, feel free to replace it
completely with something totally different and better.  (For example,
`vi' is replaced with Emacs.)  But it is nice to offer a compatible
feature as well.  (There is a free `vi' clone, so we offer it.)

   Additional useful features are welcome regardless of whether there
is any precedent for them.


File: standards.info,  Node: Using Extensions,  Next: Standard C,  Prev: Compatibility,  Up: Design Advice

3.3 Using Non-standard Features
===============================

Many GNU facilities that already exist support a number of convenient
extensions over the comparable Unix facilities.  Whether to use these
extensions in implementing your program is a difficult question.

   On the one hand, using the extensions can make a cleaner program.
On the other hand, people will not be able to build the program unless
the other GNU tools are available.  This might cause the program to
work on fewer kinds of machines.

   With some extensions, it might be easy to provide both alternatives.
For example, you can define functions with a "keyword" `INLINE' and
define that as a macro to expand into either `inline' or nothing,
depending on the compiler.

   In general, perhaps it is best not to use the extensions if you can
straightforwardly do without them, but to use the extensions if they
are a big improvement.

   An exception to this rule are the large, established programs (such
as Emacs) which run on a great variety of systems.  Using GNU
extensions in such programs would make many users unhappy, so we don't
do that.

   Another exception is for programs that are used as part of
compilation: anything that must be compiled with other compilers in
order to bootstrap the GNU compilation facilities.  If these require
the GNU compiler, then no one can compile them without having them
installed already.  That would be extremely troublesome in certain
cases.


File: standards.info,  Node: Standard C,  Next: Conditional Compilation,  Prev: Using Extensions,  Up: Design Advice

3.4 Standard C and Pre-Standard C
=================================

1989 Standard C is widespread enough now that it is ok to use its
features in new programs.  There is one exception: do not ever use the
"trigraph" feature of Standard C.

   1999 Standard C is not widespread yet, so please do not require its
features in programs.  It is ok to use its features if they are present.

   However, it is easy to support pre-standard compilers in most
programs, so if you know how to do that, feel free.  If a program you
are maintaining has such support, you should try to keep it working.

   To support pre-standard C, instead of writing function definitions in
standard prototype form,

     int
     foo (int x, int y)
     ...

write the definition in pre-standard style like this,

     int
     foo (x, y)
          int x, y;
     ...

and use a separate declaration to specify the argument prototype:

     int foo (int, int);

   You need such a declaration anyway, in a header file, to get the
benefit of prototypes in all the files where the function is called.
And once you have the declaration, you normally lose nothing by writing
the function definition in the pre-standard style.

   This technique does not work for integer types narrower than `int'.
If you think of an argument as being of a type narrower than `int',
declare it as `int' instead.

   There are a few special cases where this technique is hard to use.
For example, if a function argument needs to hold the system type
`dev_t', you run into trouble, because `dev_t' is shorter than `int' on
some machines; but you cannot use `int' instead, because `dev_t' is
wider than `int' on some machines.  There is no type you can safely use
on all machines in a non-standard definition.  The only way to support
non-standard C and pass such an argument is to check the width of
`dev_t' using Autoconf and choose the argument type accordingly.  This
may not be worth the trouble.

   In order to support pre-standard compilers that do not recognize
prototypes, you may want to use a preprocessor macro like this:

     /* Declare the prototype for a general external function.  */
     #if defined (__STDC__) || defined (WINDOWSNT)
     #define P_(proto) proto
     #else
     #define P_(proto) ()
     #endif


File: standards.info,  Node: Conditional Compilation,  Prev: Standard C,  Up: Design Advice

3.5 Conditional Compilation
===========================

When supporting configuration options already known when building your
program we prefer using `if (... )' over conditional compilation, as in
the former case the compiler is able to perform more extensive checking
of all possible code paths.

   For example, please write

       if (HAS_FOO)
         ...
       else
         ...

instead of:

       #ifdef HAS_FOO
         ...
       #else
         ...
       #endif

   A modern compiler such as GCC will generate exactly the same code in
both cases, and we have been using similar techniques with good success
in several projects.  Of course, the former method assumes that
`HAS_FOO' is defined as either 0 or 1.

   While this is not a silver bullet solving all portability problems,
and is not always appropriate, following this policy would have saved
GCC developers many hours, or even days, per year.

   In the case of function-like macros like `REVERSIBLE_CC_MODE' in GCC
which cannot be simply used in `if (...)' statements, there is an easy
workaround.  Simply introduce another macro `HAS_REVERSIBLE_CC_MODE' as
in the following example:

       #ifdef REVERSIBLE_CC_MODE
       #define HAS_REVERSIBLE_CC_MODE 1
       #else
       #define HAS_REVERSIBLE_CC_MODE 0
       #endif


File: standards.info,  Node: Program Behavior,  Next: Writing C,  Prev: Design Advice,  Up: Top

4 Program Behavior for All Programs
***********************************

This chapter describes conventions for writing robust software.  It
also describes general standards for error messages, the command line
interface, and how libraries should behave.

* Menu:

* Non-GNU Standards::           We consider standards such as POSIX;
                                  we don't "obey" them.
* Semantics::                   Writing robust programs.
* Libraries::                   Library behavior.
* Errors::                      Formatting error messages.
* User Interfaces::             Standards about interfaces generally.
* Graphical Interfaces::        Standards for graphical interfaces.
* Command-Line Interfaces::     Standards for command line interfaces.
* Option Table::                Table of long options.
* OID Allocations::             Table of OID slots for GNU.
* Memory Usage::                When and how to care about memory needs.
* File Usage::                  Which files to use, and where.


File: standards.info,  Node: Non-GNU Standards,  Next: Semantics,  Up: Program Behavior

4.1 Non-GNU Standards
=====================

The GNU Project regards standards published by other organizations as
suggestions, not orders.  We consider those standards, but we do not
"obey" them.  In developing a GNU program, you should implement an
outside standard's specifications when that makes the GNU system better
overall in an objective sense.  When it doesn't, you shouldn't.

   In most cases, following published standards is convenient for
users--it means that their programs or scripts will work more portably.
For instance, GCC implements nearly all the features of Standard C as
specified by that standard.  C program developers would be unhappy if
it did not.  And GNU utilities mostly follow specifications of POSIX.2;
shell script writers and users would be unhappy if our programs were
incompatible.

   But we do not follow either of these specifications rigidly, and
there are specific points on which we decided not to follow them, so as
to make the GNU system better for users.

   For instance, Standard C says that nearly all extensions to C are
prohibited.  How silly!  GCC implements many extensions, some of which
were later adopted as part of the standard.  If you want these
constructs to give an error message as "required" by the standard, you
must specify `--pedantic', which was implemented only so that we can
say "GCC is a 100% implementation of the standard," not because there
is any reason to actually use it.

   POSIX.2 specifies that `df' and `du' must output sizes by default in
units of 512 bytes.  What users want is units of 1k, so that is what we
do by default.  If you want the ridiculous behavior "required" by
POSIX, you must set the environment variable `POSIXLY_CORRECT' (which
was originally going to be named `POSIX_ME_HARDER').

   GNU utilities also depart from the letter of the POSIX.2
specification when they support long-named command-line options, and
intermixing options with ordinary arguments.  This minor
incompatibility with POSIX is never a problem in practice, and it is
very useful.

   In particular, don't reject a new feature, or remove an old one,
merely because a standard says it is "forbidden" or "deprecated."


File: standards.info,  Node: Semantics,  Next: Libraries,  Prev: Non-GNU Standards,  Up: Program Behavior

4.2 Writing Robust Programs
===========================

Avoid arbitrary limits on the length or number of _any_ data structure,
including file names, lines, files, and symbols, by allocating all data
structures dynamically.  In most Unix utilities, "long lines are
silently truncated".  This is not acceptable in a GNU utility.

   Utilities reading files should not drop NUL characters, or any other
nonprinting characters _including those with codes above 0177_.  The
only sensible exceptions would be utilities specifically intended for
interface to certain types of terminals or printers that can't handle
those characters.  Whenever possible, try to make programs work
properly with sequences of bytes that represent multibyte characters,
using encodings such as UTF-8 and others.

   Check every system call for an error return, unless you know you
wish to ignore errors.  Include the system error text (from `perror' or
equivalent) in _every_ error message resulting from a failing system
call, as well as the name of the file if any and the name of the
utility.  Just "cannot open foo.c" or "stat failed" is not sufficient.

   Check every call to `malloc' or `realloc' to see if it returned
zero.  Check `realloc' even if you are making the block smaller; in a
system that rounds block sizes to a power of 2, `realloc' may get a
different block if you ask for less space.

   In Unix, `realloc' can destroy the storage block if it returns zero.
GNU `realloc' does not have this bug: if it fails, the original block
is unchanged.  Feel free to assume the bug is fixed.  If you wish to
run your program on Unix, and wish to avoid lossage in this case, you
can use the GNU `malloc'.

   You must expect `free' to alter the contents of the block that was
freed.  Anything you want to fetch from the block, you must fetch before
calling `free'.

   If `malloc' fails in a noninteractive program, make that a fatal
error.  In an interactive program (one that reads commands from the
user), it is better to abort the command and return to the command
reader loop.  This allows the user to kill other processes to free up
virtual memory, and then try the command again.

   Use `getopt_long' to decode arguments, unless the argument syntax
makes this unreasonable.

   When static storage is to be written in during program execution, use
explicit C code to initialize it.  Reserve C initialized declarations
for data that will not be changed.

   Try to avoid low-level interfaces to obscure Unix data structures
(such as file directories, utmp, or the layout of kernel memory), since
these are less likely to work compatibly.  If you need to find all the
files in a directory, use `readdir' or some other high-level interface.
These are supported compatibly by GNU.

   The preferred signal handling facilities are the BSD variant of
`signal', and the POSIX `sigaction' function; the alternative USG
`signal' interface is an inferior design.

   Nowadays, using the POSIX signal functions may be the easiest way to
make a program portable.  If you use `signal', then on GNU/Linux
systems running GNU libc version 1, you should include `bsd/signal.h'
instead of `signal.h', so as to get BSD behavior.  It is up to you
whether to support systems where `signal' has only the USG behavior, or
give up on them.

   In error checks that detect "impossible" conditions, just abort.
There is usually no point in printing any message.  These checks
indicate the existence of bugs.  Whoever wants to fix the bugs will have
to read the source code and run a debugger.  So explain the problem with
comments in the source.  The relevant data will be in variables, which
are easy to examine with the debugger, so there is no point moving them
elsewhere.

   Do not use a count of errors as the exit status for a program.
_That does not work_, because exit status values are limited to 8 bits
(0 through 255).  A single run of the program might have 256 errors; if
you try to return 256 as the exit status, the parent process will see 0
as the status, and it will appear that the program succeeded.

   If you make temporary files, check the `TMPDIR' environment
variable; if that variable is defined, use the specified directory
instead of `/tmp'.

   In addition, be aware that there is a possible security problem when
creating temporary files in world-writable directories.  In C, you can
avoid this problem by creating temporary files in this manner:

     fd = open (filename, O_WRONLY | O_CREAT | O_EXCL, 0600);

or by using the `mkstemps' function from libiberty.

   In bash, use `set -C' to avoid this problem.


File: standards.info,  Node: Libraries,  Next: Errors,  Prev: Semantics,  Up: Program Behavior

4.3 Library Behavior
====================

Try to make library functions reentrant.  If they need to do dynamic
storage allocation, at least try to avoid any nonreentrancy aside from
that of `malloc' itself.

   Here are certain name conventions for libraries, to avoid name
conflicts.

   Choose a name prefix for the library, more than two characters long.
All external function and variable names should start with this prefix.
In addition, there should only be one of these in any given library
member.  This usually means putting each one in a separate source file.

   An exception can be made when two external symbols are always used
together, so that no reasonable program could use one without the
other; then they can both go in the same file.

   External symbols that are not documented entry points for the user
should have names beginning with `_'.  The `_' should be followed by
the chosen name prefix for the library, to prevent collisions with
other libraries.  These can go in the same files with user entry points
if you like.

   Static functions and variables can be used as you like and need not
fit any naming convention.


File: standards.info,  Node: Errors,  Next: User Interfaces,  Prev: Libraries,  Up: Program Behavior

4.4 Formatting Error Messages
=============================

Error messages from compilers should look like this:

     SOURCE-FILE-NAME:LINENO: MESSAGE

If you want to mention the column number, use one of these formats:

     SOURCE-FILE-NAME:LINENO:COLUMN: MESSAGE
     SOURCE-FILE-NAME:LINENO.COLUMN: MESSAGE

Line numbers should start from 1 at the beginning of the file, and
column numbers should start from 1 at the beginning of the line.  (Both
of these conventions are chosen for compatibility.)  Calculate column
numbers assuming that space and all ASCII printing characters have
equal width, and assuming tab stops every 8 columns.

   The error message can also give both the starting and ending
positions of the erroneous text.  There are several formats so that you
can avoid redundant information such as a duplicate line number.  Here
are the possible formats:

     SOURCE-FILE-NAME:LINENO-1.COLUMN-1-LINENO-2.COLUMN-2: MESSAGE
     SOURCE-FILE-NAME:LINENO-1.COLUMN-1-COLUMN-2: MESSAGE
     SOURCE-FILE-NAME:LINENO-1-LINENO-2: MESSAGE

When an error is spread over several files, you can use this format:

     FILE-1:LINENO-1.COLUMN-1-FILE-2:LINENO-2.COLUMN-2: MESSAGE

   Error messages from other noninteractive programs should look like
this:

     PROGRAM:SOURCE-FILE-NAME:LINENO: MESSAGE

when there is an appropriate source file, or like this:

     PROGRAM: MESSAGE

when there is no relevant source file.

   If you want to mention the column number, use this format:

     PROGRAM:SOURCE-FILE-NAME:LINENO:COLUMN: MESSAGE

   In an interactive program (one that is reading commands from a
terminal), it is better not to include the program name in an error
message.  The place to indicate which program is running is in the
prompt or with the screen layout.  (When the same program runs with
input from a source other than a terminal, it is not interactive and
would do best to print error messages using the noninteractive style.)

   The string MESSAGE should not begin with a capital letter when it
follows a program name and/or file name, because that isn't the
beginning of a sentence.  (The sentence conceptually starts at the
beginning of the line.)  Also, it should not end with a period.

   Error messages from interactive programs, and other messages such as
usage messages, should start with a capital letter.  But they should not
end with a period.


File: standards.info,  Node: User Interfaces,  Next: Graphical Interfaces,  Prev: Errors,  Up: Program Behavior

4.5 Standards for Interfaces Generally
======================================

Please don't make the behavior of a utility depend on the name used to
invoke it.  It is useful sometimes to make a link to a utility with a
different name, and that should not change what it does.

   Instead, use a run time option or a compilation switch or both to
select among the alternate behaviors.

   Likewise, please don't make the behavior of the program depend on the
type of output device it is used with.  Device independence is an
important principle of the system's design; do not compromise it merely
to save someone from typing an option now and then.  (Variation in error
message syntax when using a terminal is ok, because that is a side issue
that people do not depend on.)

   If you think one behavior is most useful when the output is to a
terminal, and another is most useful when the output is a file or a
pipe, then it is usually best to make the default behavior the one that
is useful with output to a terminal, and have an option for the other
behavior.

   Compatibility requires certain programs to depend on the type of
output device.  It would be disastrous if `ls' or `sh' did not do so in
the way all users expect.  In some of these cases, we supplement the
program with a preferred alternate version that does not depend on the
output device type.  For example, we provide a `dir' program much like
`ls' except that its default output format is always multi-column
format.


File: standards.info,  Node: Graphical Interfaces,  Next: Command-Line Interfaces,  Prev: User Interfaces,  Up: Program Behavior

4.6 Standards for Graphical Interfaces
======================================

When you write a program that provides a graphical user interface,
please make it work with the X Window System and the GTK+ toolkit
unless the functionality specifically requires some alternative (for
example, "displaying jpeg images while in console mode").

   In addition, please provide a command-line interface to control the
functionality.  (In many cases, the graphical user interface can be a
separate program which invokes the command-line program.)  This is so
that the same jobs can be done from scripts.

   Please also consider providing a D-bus interface for use from other
running programs, such as within GNOME.  (GNOME used to use CORBA for
this, but that is being phased out.)  In addition, consider providing a
library interface (for use from C), and perhaps a keyboard-driven
console interface (for use by users from console mode).  Once you are
doing the work to provide the functionality and the graphical
interface, these won't be much extra work.


File: standards.info,  Node: Command-Line Interfaces,  Next: Option Table,  Prev: Graphical Interfaces,  Up: Program Behavior

4.7 Standards for Command Line Interfaces
=========================================

It is a good idea to follow the POSIX guidelines for the command-line
options of a program.  The easiest way to do this is to use `getopt' to
parse them.  Note that the GNU version of `getopt' will normally permit
options anywhere among the arguments unless the special argument `--'
is used.  This is not what POSIX specifies; it is a GNU extension.

   Please define long-named options that are equivalent to the
single-letter Unix-style options.  We hope to make GNU more user
friendly this way.  This is easy to do with the GNU function
`getopt_long'.

   One of the advantages of long-named options is that they can be
consistent from program to program.  For example, users should be able
to expect the "verbose" option of any GNU program which has one, to be
spelled precisely `--verbose'.  To achieve this uniformity, look at the
table of common long-option names when you choose the option names for
your program (*note Option Table::).

   It is usually a good idea for file names given as ordinary arguments
to be input files only; any output files would be specified using
options (preferably `-o' or `--output').  Even if you allow an output
file name as an ordinary argument for compatibility, try to provide an
option as another way to specify it.  This will lead to more consistency
among GNU utilities, and fewer idiosyncrasies for users to remember.

   All programs should support two standard options: `--version' and
`--help'.  CGI programs should accept these as command-line options,
and also if given as the `PATH_INFO'; for instance, visiting
`http://example.org/p.cgi/--help' in a browser should output the same
information as invoking `p.cgi --help' from the command line.

* Menu:

* --version::       The standard output for --version.
* --help::          The standard output for --help.


File: standards.info,  Node: --version,  Next: --help,  Up: Command-Line Interfaces

4.7.1 `--version'
-----------------

The standard `--version' option should direct the program to print
information about its name, version, origin and legal status, all on
standard output, and then exit successfully.  Other options and
arguments should be ignored once this is seen, and the program should
not perform its normal function.

   The first line is meant to be easy for a program to parse; the
version number proper starts after the last space.  In addition, it
contains the canonical name for this program, in this format:

     GNU Emacs 19.30

The program's name should be a constant string; _don't_ compute it from
`argv[0]'.  The idea is to state the standard or canonical name for the
program, not its file name.  There are other ways to find out the
precise file name where a command is found in `PATH'.

   If the program is a subsidiary part of a larger package, mention the
package name in parentheses, like this:

     emacsserver (GNU Emacs) 19.30

If the package has a version number which is different from this
program's version number, you can mention the package version number
just before the close-parenthesis.

   If you _need_ to mention the version numbers of libraries which are
distributed separately from the package which contains this program,
you can do so by printing an additional line of version info for each
library you want to mention.  Use the same format for these lines as for
the first line.

   Please do not mention all of the libraries that the program uses
"just for completeness"--that would produce a lot of unhelpful clutter.
Please mention library version numbers only if you find in practice that
they are very important to you in debugging.

   The following line, after the version number line or lines, should
be a copyright notice.  If more than one copyright notice is called
for, put each on a separate line.

   Next should follow a line stating the license, preferably using one
of abbrevations below, and a brief statement that the program is free
software, and that users are free to copy and change it.  Also mention
that there is no warranty, to the extent permitted by law.  See
recommended wording below.

   It is ok to finish the output with a list of the major authors of the
program, as a way of giving credit.

   Here's an example of output that follows these rules:

     GNU hello 2.3
     Copyright (C) 2007 Free Software Foundation, Inc.
     License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
     This is free software: you are free to change and redistribute it.
     There is NO WARRANTY, to the extent permitted by law.

   You should adapt this to your program, of course, filling in the
proper year, copyright holder, name of program, and the references to
distribution terms, and changing the rest of the wording as necessary.

   This copyright notice only needs to mention the most recent year in
which changes were made--there's no need to list the years for previous
versions' changes.  You don't have to mention the name of the program in
these notices, if that is inconvenient, since it appeared in the first
line.  (The rules are different for copyright notices in source files;
*note Copyright Notices: (maintain)Copyright Notices.)

   Translations of the above lines must preserve the validity of the
copyright notices (*note Internationalization::).  If the translation's
character set supports it, the `(C)' should be replaced with the
copyright symbol, as follows:

   (the official copyright symbol, which is the letter C in a circle);

   Write the word "Copyright" exactly like that, in English.  Do not
translate it into another language.  International treaties recognize
the English word "Copyright"; translations into other languages do not
have legal significance.

   Finally, here is the table of our suggested license abbreviations.
Any abbreviation can be followed by `vVERSION[+]', meaning that
particular version, or later versions with the `+', as shown above.

   In the case of exceptions for extra permissions with the GPL, we use
`/' for a separator; the version number can follow the license
abbreviation as usual, as in the examples below.

GPL
     GNU General Public License, `http://www.gnu.org/licenses/gpl.html'.

LGPL
     GNU Lesser General Public License,
     `http://www.gnu.org/licenses/lgpl.html'.

GPL/Ada
     GNU GPL with the exception for Ada.

Apache
     The Apache Software Foundation license,
     `http://www.apache.org/licenses'.

Artistic
     The Artistic license used for Perl,
     `http://www.perlfoundation.org/legal'.

Expat
     The Expat license, `http://www.jclark.com/xml/copying.txt'.

MPL
     The Mozilla Public License, `http://www.mozilla.org/MPL/'.

OBSD
     The original (4-clause) BSD license, incompatible with the GNU GPL
     `http://www.xfree86.org/3.3.6/COPYRIGHT2.html#6'.

PHP
     The license used for PHP, `http://www.php.net/license/'.

public domain
     The non-license that is being in the public domain,
     `http://www.gnu.org/licenses/license-list.html#PublicDomain'.

Python
     The license for Python, `http://www.python.org/2.0.1/license.html'.

RBSD
     The revised (3-clause) BSD, compatible with the GNU GPL,
     `http://www.xfree86.org/3.3.6/COPYRIGHT2.html#5'.

X11
     The simple non-copyleft license used for most versions of the X
     Window System, `http://www.xfree86.org/3.3.6/COPYRIGHT2.html#3'.

Zlib
     The license for Zlib, `http://www.gzip.org/zlib/zlib_license.html'.


   More information about these licenses and many more are on the GNU
licensing web pages, `http://www.gnu.org/licenses/license-list.html'.


File: standards.info,  Node: --help,  Prev: --version,  Up: Command-Line Interfaces

4.7.2 `--help'
--------------

The standard `--help' option should output brief documentation for how
to invoke the program, on standard output, then exit successfully.
Other options and arguments should be ignored once this is seen, and
the program should not perform its normal function.

   Near the end of the `--help' option's output, please place lines
giving the email address for bug reports, the package's home page
(normally <http://www.gnu.org/software/PKG>, and the general page for
help using GNU programs.  The format should be like this:

     Report bugs to: MAILING-ADDRESS
     PKG home page: <http://www.gnu.org/software/PKG/>
     General help using GNU software: <http://www.gnu.org/gethelp/>

   It is ok to mention other appropriate mailing lists and web pages.


File: standards.info,  Node: Option Table,  Next: OID Allocations,  Prev: Command-Line Interfaces,  Up: Program Behavior

4.8 Table of Long Options
=========================

Here is a table of long options used by GNU programs.  It is surely
incomplete, but we aim to list all the options that a new program might
want to be compatible with.  If you use names not already in the table,
please send <bug-standards@gnu.org> a list of them, with their
meanings, so we can update the table.

`after-date'
     `-N' in `tar'.

`all'
     `-a' in `du', `ls', `nm', `stty', `uname', and `unexpand'.

`all-text'
     `-a' in `diff'.

`almost-all'
     `-A' in `ls'.

`append'
     `-a' in `etags', `tee', `time'; `-r' in `tar'.

`archive'
     `-a' in `cp'.

`archive-name'
     `-n' in `shar'.

`arglength'
     `-l' in `m4'.

`ascii'
     `-a' in `diff'.

`assign'
     `-v' in `gawk'.

`assume-new'
     `-W' in `make'.

`assume-old'
     `-o' in `make'.

`auto-check'
     `-a' in `recode'.

`auto-pager'
     `-a' in `wdiff'.

`auto-reference'
     `-A' in `ptx'.

`avoid-wraps'
     `-n' in `wdiff'.

`background'
     For server programs, run in the background.

`backward-search'
     `-B' in `ctags'.

`basename'
     `-f' in `shar'.

`batch'
     Used in GDB.

`baud'
     Used in GDB.

`before'
     `-b' in `tac'.

`binary'
     `-b' in `cpio' and `diff'.

`bits-per-code'
     `-b' in `shar'.

`block-size'
     Used in `cpio' and `tar'.

`blocks'
     `-b' in `head' and `tail'.

`break-file'
     `-b' in `ptx'.

`brief'
     Used in various programs to make output shorter.

`bytes'
     `-c' in `head', `split', and `tail'.

`c++'
     `-C' in `etags'.

`catenate'
     `-A' in `tar'.

`cd'
     Used in various programs to specify the directory to use.

`changes'
     `-c' in `chgrp' and `chown'.

`classify'
     `-F' in `ls'.

`colons'
     `-c' in `recode'.

`command'
     `-c' in `su'; `-x' in GDB.

`compare'
     `-d' in `tar'.

`compat'
     Used in `gawk'.

`compress'
     `-Z' in `tar' and `shar'.

`concatenate'
     `-A' in `tar'.

`confirmation'
     `-w' in `tar'.

`context'
     Used in `diff'.

`copyleft'
     `-W copyleft' in `gawk'.

`copyright'
     `-C' in `ptx', `recode', and `wdiff'; `-W copyright' in `gawk'.

`core'
     Used in GDB.

`count'
     `-q' in `who'.

`count-links'
     `-l' in `du'.

`create'
     Used in `tar' and `cpio'.

`cut-mark'
     `-c' in `shar'.

`cxref'
     `-x' in `ctags'.

`date'
     `-d' in `touch'.

`debug'
     `-d' in `make' and `m4'; `-t' in Bison.

`define'
     `-D' in `m4'.

`defines'
     `-d' in Bison and `ctags'.

`delete'
     `-D' in `tar'.

`dereference'
     `-L' in `chgrp', `chown', `cpio', `du', `ls', and `tar'.

`dereference-args'
     `-D' in `du'.

`device'
     Specify an I/O device (special file name).

`diacritics'
     `-d' in `recode'.

`dictionary-order'
     `-d' in `look'.

`diff'
     `-d' in `tar'.

`digits'
     `-n' in `csplit'.

`directory'
     Specify the directory to use, in various programs.  In `ls', it
     means to show directories themselves rather than their contents.
     In `rm' and `ln', it means to not treat links to directories
     specially.

`discard-all'
     `-x' in `strip'.

`discard-locals'
     `-X' in `strip'.

`dry-run'
     `-n' in `make'.

`ed'
     `-e' in `diff'.

`elide-empty-files'
     `-z' in `csplit'.

`end-delete'
     `-x' in `wdiff'.

`end-insert'
     `-z' in `wdiff'.

`entire-new-file'
     `-N' in `diff'.

`environment-overrides'
     `-e' in `make'.

`eof'
     `-e' in `xargs'.

`epoch'
     Used in GDB.

`error-limit'
     Used in `makeinfo'.

`error-output'
     `-o' in `m4'.

`escape'
     `-b' in `ls'.

`exclude-from'
     `-X' in `tar'.

`exec'
     Used in GDB.

`exit'
     `-x' in `xargs'.

`exit-0'
     `-e' in `unshar'.

`expand-tabs'
     `-t' in `diff'.

`expression'
     `-e' in `sed'.

`extern-only'
     `-g' in `nm'.

`extract'
     `-i' in `cpio'; `-x' in `tar'.

`faces'
     `-f' in `finger'.

`fast'
     `-f' in `su'.

`fatal-warnings'
     `-E' in `m4'.

`file'
     `-f' in `gawk', `info', `make', `mt', `sed', and `tar'.

`field-separator'
     `-F' in `gawk'.

`file-prefix'
     `-b' in Bison.

`file-type'
     `-F' in `ls'.

`files-from'
     `-T' in `tar'.

`fill-column'
     Used in `makeinfo'.

`flag-truncation'
     `-F' in `ptx'.

`fixed-output-files'
     `-y' in Bison.

`follow'
     `-f' in `tail'.

`footnote-style'
     Used in `makeinfo'.

`force'
     `-f' in `cp', `ln', `mv', and `rm'.

`force-prefix'
     `-F' in `shar'.

`foreground'
     For server programs, run in the foreground; in other words, don't
     do anything special to run the server in the background.

`format'
     Used in `ls', `time', and `ptx'.

`freeze-state'
     `-F' in `m4'.

`fullname'
     Used in GDB.

`gap-size'
     `-g' in `ptx'.

`get'
     `-x' in `tar'.

`graphic'
     `-i' in `ul'.

`graphics'
     `-g' in `recode'.

`group'
     `-g' in `install'.

`gzip'
     `-z' in `tar' and `shar'.

`hashsize'
     `-H' in `m4'.

`header'
     `-h' in `objdump' and `recode'

`heading'
     `-H' in `who'.

`help'
     Used to ask for brief usage information.

`here-delimiter'
     `-d' in `shar'.

`hide-control-chars'
     `-q' in `ls'.

`html'
     In `makeinfo', output HTML.

`idle'
     `-u' in `who'.

`ifdef'
     `-D' in `diff'.

`ignore'
     `-I' in `ls'; `-x' in `recode'.

`ignore-all-space'
     `-w' in `diff'.

`ignore-backups'
     `-B' in `ls'.

`ignore-blank-lines'
     `-B' in `diff'.

`ignore-case'
     `-f' in `look' and `ptx'; `-i' in `diff' and `wdiff'.

`ignore-errors'
     `-i' in `make'.

`ignore-file'
     `-i' in `ptx'.

`ignore-indentation'
     `-I' in `etags'.

`ignore-init-file'
     `-f' in Oleo.

`ignore-interrupts'
     `-i' in `tee'.

`ignore-matching-lines'
     `-I' in `diff'.

`ignore-space-change'
     `-b' in `diff'.

`ignore-zeros'
     `-i' in `tar'.

`include'
     `-i' in `etags'; `-I' in `m4'.

`include-dir'
     `-I' in `make'.

`incremental'
     `-G' in `tar'.

`info'
     `-i', `-l', and `-m' in Finger.

`init-file'
     In some programs, specify the name of the file to read as the
     user's init file.

`initial'
     `-i' in `expand'.

`initial-tab'
     `-T' in `diff'.

`inode'
     `-i' in `ls'.

`interactive'
     `-i' in `cp', `ln', `mv', `rm'; `-e' in `m4'; `-p' in `xargs';
     `-w' in `tar'.

`intermix-type'
     `-p' in `shar'.

`iso-8601'
     Used in `date'

`jobs'
     `-j' in `make'.

`just-print'
     `-n' in `make'.

`keep-going'
     `-k' in `make'.

`keep-files'
     `-k' in `csplit'.

`kilobytes'
     `-k' in `du' and `ls'.

`language'
     `-l' in `etags'.

`less-mode'
     `-l' in `wdiff'.

`level-for-gzip'
     `-g' in `shar'.

`line-bytes'
     `-C' in `split'.

`lines'
     Used in `split', `head', and `tail'.

`link'
     `-l' in `cpio'.

`lint'
`lint-old'
     Used in `gawk'.

`list'
     `-t' in `cpio'; `-l' in `recode'.

`list'
     `-t' in `tar'.

`literal'
     `-N' in `ls'.

`load-average'
     `-l' in `make'.

`login'
     Used in `su'.

`machine'
     Used in `uname'.

`macro-name'
     `-M' in `ptx'.

`mail'
     `-m' in `hello' and `uname'.

`make-directories'
     `-d' in `cpio'.

`makefile'
     `-f' in `make'.

`mapped'
     Used in GDB.

`max-args'
     `-n' in `xargs'.

`max-chars'
     `-n' in `xargs'.

`max-lines'
     `-l' in `xargs'.

`max-load'
     `-l' in `make'.

`max-procs'
     `-P' in `xargs'.

`mesg'
     `-T' in `who'.

`message'
     `-T' in `who'.

`minimal'
     `-d' in `diff'.

`mixed-uuencode'
     `-M' in `shar'.

`mode'
     `-m' in `install', `mkdir', and `mkfifo'.

`modification-time'
     `-m' in `tar'.

`multi-volume'
     `-M' in `tar'.

`name-prefix'
     `-a' in Bison.

`nesting-limit'
     `-L' in `m4'.

`net-headers'
     `-a' in `shar'.

`new-file'
     `-W' in `make'.

`no-builtin-rules'
     `-r' in `make'.

`no-character-count'
     `-w' in `shar'.

`no-check-existing'
     `-x' in `shar'.

`no-common'
     `-3' in `wdiff'.

`no-create'
     `-c' in `touch'.

`no-defines'
     `-D' in `etags'.

`no-deleted'
     `-1' in `wdiff'.

`no-dereference'
     `-d' in `cp'.

`no-inserted'
     `-2' in `wdiff'.

`no-keep-going'
     `-S' in `make'.

`no-lines'
     `-l' in Bison.

`no-piping'
     `-P' in `shar'.

`no-prof'
     `-e' in `gprof'.

`no-regex'
     `-R' in `etags'.

`no-sort'
     `-p' in `nm'.

`no-splash'
     Don't print a startup splash screen.

`no-split'
     Used in `makeinfo'.

`no-static'
     `-a' in `gprof'.

`no-time'
     `-E' in `gprof'.

`no-timestamp'
     `-m' in `shar'.

`no-validate'
     Used in `makeinfo'.

`no-wait'
     Used in `emacsclient'.

`no-warn'
     Used in various programs to inhibit warnings.

`node'
     `-n' in `info'.

`nodename'
     `-n' in `uname'.

`nonmatching'
     `-f' in `cpio'.

`nstuff'
     `-n' in `objdump'.

`null'
     `-0' in `xargs'.

`number'
     `-n' in `cat'.

`number-nonblank'
     `-b' in `cat'.

`numeric-sort'
     `-n' in `nm'.

`numeric-uid-gid'
     `-n' in `cpio' and `ls'.

`nx'
     Used in GDB.

`old-archive'
     `-o' in `tar'.

`old-file'
     `-o' in `make'.

`one-file-system'
     `-l' in `tar', `cp', and `du'.

`only-file'
     `-o' in `ptx'.

`only-prof'
     `-f' in `gprof'.

`only-time'
     `-F' in `gprof'.

`options'
     `-o' in `getopt', `fdlist', `fdmount', `fdmountd', and `fdumount'.

`output'
     In various programs, specify the output file name.

`output-prefix'
     `-o' in `shar'.

`override'
     `-o' in `rm'.

`overwrite'
     `-c' in `unshar'.

`owner'
     `-o' in `install'.

`paginate'
     `-l' in `diff'.

`paragraph-indent'
     Used in `makeinfo'.

`parents'
     `-p' in `mkdir' and `rmdir'.

`pass-all'
     `-p' in `ul'.

`pass-through'
     `-p' in `cpio'.

`port'
     `-P' in `finger'.

`portability'
     `-c' in `cpio' and `tar'.

`posix'
     Used in `gawk'.

`prefix-builtins'
     `-P' in `m4'.

`prefix'
     `-f' in `csplit'.

`preserve'
     Used in `tar' and `cp'.

`preserve-environment'
     `-p' in `su'.

`preserve-modification-time'
     `-m' in `cpio'.

`preserve-order'
     `-s' in `tar'.

`preserve-permissions'
     `-p' in `tar'.

`print'
     `-l' in `diff'.

`print-chars'
     `-L' in `cmp'.

`print-data-base'
     `-p' in `make'.

`print-directory'
     `-w' in `make'.

`print-file-name'
     `-o' in `nm'.

`print-symdefs'
     `-s' in `nm'.

`printer'
     `-p' in `wdiff'.

`prompt'
     `-p' in `ed'.

`proxy'
     Specify an HTTP proxy.

`query-user'
     `-X' in `shar'.

`question'
     `-q' in `make'.

`quiet'
     Used in many programs to inhibit the usual output.  Every program
     accepting `--quiet' should accept `--silent' as a synonym.

`quiet-unshar'
     `-Q' in `shar'

`quote-name'
     `-Q' in `ls'.

`rcs'
     `-n' in `diff'.

`re-interval'
     Used in `gawk'.

`read-full-blocks'
     `-B' in `tar'.

`readnow'
     Used in GDB.

`recon'
     `-n' in `make'.

`record-number'
     `-R' in `tar'.

`recursive'
     Used in `chgrp', `chown', `cp', `ls', `diff', and `rm'.

`reference'
     `-r' in `touch'.

`references'
     `-r' in `ptx'.

`regex'
     `-r' in `tac' and `etags'.

`release'
     `-r' in `uname'.

`reload-state'
     `-R' in `m4'.

`relocation'
     `-r' in `objdump'.

`rename'
     `-r' in `cpio'.

`replace'
     `-i' in `xargs'.

`report-identical-files'
     `-s' in `diff'.

`reset-access-time'
     `-a' in `cpio'.

`reverse'
     `-r' in `ls' and `nm'.

`reversed-ed'
     `-f' in `diff'.

`right-side-defs'
     `-R' in `ptx'.

`same-order'
     `-s' in `tar'.

`same-permissions'
     `-p' in `tar'.

`save'
     `-g' in `stty'.

`se'
     Used in GDB.

`sentence-regexp'
     `-S' in `ptx'.

`separate-dirs'
     `-S' in `du'.

`separator'
     `-s' in `tac'.

`sequence'
     Used by `recode' to chose files or pipes for sequencing passes.

`shell'
     `-s' in `su'.

`show-all'
     `-A' in `cat'.

`show-c-function'
     `-p' in `diff'.

`show-ends'
     `-E' in `cat'.

`show-function-line'
     `-F' in `diff'.

`show-tabs'
     `-T' in `cat'.

`silent'
     Used in many programs to inhibit the usual output.  Every program
     accepting `--silent' should accept `--quiet' as a synonym.

`size'
     `-s' in `ls'.

`socket'
     Specify a file descriptor for a network server to use for its
     socket, instead of opening and binding a new socket.  This
     provides a way to run, in a non-privileged process, a server that
     normally needs a reserved port number.

`sort'
     Used in `ls'.

`source'
     `-W source' in `gawk'.

`sparse'
     `-S' in `tar'.

`speed-large-files'
     `-H' in `diff'.

`split-at'
     `-E' in `unshar'.

`split-size-limit'
     `-L' in `shar'.

`squeeze-blank'
     `-s' in `cat'.

`start-delete'
     `-w' in `wdiff'.

`start-insert'
     `-y' in `wdiff'.

`starting-file'
     Used in `tar' and `diff' to specify which file within a directory
     to start processing with.

`statistics'
     `-s' in `wdiff'.

`stdin-file-list'
     `-S' in `shar'.

`stop'
     `-S' in `make'.

`strict'
     `-s' in `recode'.

`strip'
     `-s' in `install'.

`strip-all'
     `-s' in `strip'.

`strip-debug'
     `-S' in `strip'.

`submitter'
     `-s' in `shar'.

`suffix'
     `-S' in `cp', `ln', `mv'.

`suffix-format'
     `-b' in `csplit'.

`sum'
     `-s' in `gprof'.

`summarize'
     `-s' in `du'.

`symbolic'
     `-s' in `ln'.

`symbols'
     Used in GDB and `objdump'.

`synclines'
     `-s' in `m4'.

`sysname'
     `-s' in `uname'.

`tabs'
     `-t' in `expand' and `unexpand'.

`tabsize'
     `-T' in `ls'.

`terminal'
     `-T' in `tput' and `ul'.  `-t' in `wdiff'.

`text'
     `-a' in `diff'.

`text-files'
     `-T' in `shar'.

`time'
     Used in `ls' and `touch'.

`timeout'
     Specify how long to wait before giving up on some operation.

`to-stdout'
     `-O' in `tar'.

`total'
     `-c' in `du'.

`touch'
     `-t' in `make', `ranlib', and `recode'.

`trace'
     `-t' in `m4'.

`traditional'
     `-t' in `hello'; `-W traditional' in `gawk'; `-G' in `ed', `m4',
     and `ptx'.

`tty'
     Used in GDB.

`typedefs'
     `-t' in `ctags'.

`typedefs-and-c++'
     `-T' in `ctags'.

`typeset-mode'
     `-t' in `ptx'.

`uncompress'
     `-z' in `tar'.

`unconditional'
     `-u' in `cpio'.

`undefine'
     `-U' in `m4'.

`undefined-only'
     `-u' in `nm'.

`update'
     `-u' in `cp', `ctags', `mv', `tar'.

`usage'
     Used in `gawk'; same as `--help'.

`uuencode'
     `-B' in `shar'.

`vanilla-operation'
     `-V' in `shar'.

`verbose'
     Print more information about progress.  Many programs support this.

`verify'
     `-W' in `tar'.

`version'
     Print the version number.

`version-control'
     `-V' in `cp', `ln', `mv'.

`vgrind'
     `-v' in `ctags'.

`volume'
     `-V' in `tar'.

`what-if'
     `-W' in `make'.

`whole-size-limit'
     `-l' in `shar'.

`width'
     `-w' in `ls' and `ptx'.

`word-regexp'
     `-W' in `ptx'.

`writable'
     `-T' in `who'.

`zeros'
     `-z' in `gprof'.


File: standards.info,  Node: OID Allocations,  Next: Memory Usage,  Prev: Option Table,  Up: Program Behavior

4.9 OID Allocations
===================

The OID (object identifier) 1.3.6.1.4.1.11591 has been assigned to the
GNU Project (thanks to Werner Koch).  These are used for SNMP, LDAP,
X.509 certificates, and so on.  The web site
`http://www.alvestrand.no/objectid' has a (voluntary) listing of many
OID assignments.

   If you need a new slot for your GNU package, write
<maintainers@gnu.org>.  Here is a list of arcs currently assigned:


     1.3.6.1.4.1.11591 GNU

     1.3.6.1.4.1.11591.1 GNU Radius

     1.3.6.1.4.1.11591.2 GnuPG
       1.3.6.1.4.1.11591.2.1   notation
       1.3.6.1.4.1.11591.2.1.1 pkaAddress

     1.3.6.1.4.1.11591.3 GNU Radar

     1.3.6.1.4.1.11591.4 GNU GSS

     1.3.6.1.4.1.11591.5 GNU Mailutils

     1.3.6.1.4.1.11591.6 GNU Shishi

     1.3.6.1.4.1.11591.7 GNU Radio

     1.3.6.1.4.1.11591.12 digestAlgorithm
       1.3.6.1.4.1.11591.12.2 TIGER/192
       1.3.6.1.4.1.11591.13 encryptionAlgorithm
         1.3.6.1.4.1.11591.13.2 Serpent
           1.3.6.1.4.1.11591.13.2.1 Serpent-128-ECB
           1.3.6.1.4.1.11591.13.2.2 Serpent-128-CBC
           1.3.6.1.4.1.11591.13.2.3 Serpent-128-OFB
           1.3.6.1.4.1.11591.13.2.4 Serpent-128-CFB
           1.3.6.1.4.1.11591.13.2.21 Serpent-192-ECB
           1.3.6.1.4.1.11591.13.2.22 Serpent-192-CBC
           1.3.6.1.4.1.11591.13.2.23 Serpent-192-OFB
           1.3.6.1.4.1.11591.13.2.24 Serpent-192-CFB
           1.3.6.1.4.1.11591.13.2.41 Serpent-256-ECB
           1.3.6.1.4.1.11591.13.2.42 Serpent-256-CBC
           1.3.6.1.4.1.11591.13.2.43 Serpent-256-OFB
           1.3.6.1.4.1.11591.13.2.44 Serpent-256-CFB
       1.3.6.1.4.1.11591.14 CRC algorithms
         1.3.6.1.4.1.11591.14.1 CRC 32


File: standards.info,  Node: Memory Usage,  Next: File Usage,  Prev: OID Allocations,  Up: Program Behavior

4.10 Memory Usage
=================

If a program typically uses just a few meg of memory, don't bother
making any effort to reduce memory usage.  For example, if it is
impractical for other reasons to operate on files more than a few meg
long, it is reasonable to read entire input files into memory to
operate on them.

   However, for programs such as `cat' or `tail', that can usefully
operate on very large files, it is important to avoid using a technique
that would artificially limit the size of files it can handle.  If a
program works by lines and could be applied to arbitrary user-supplied
input files, it should keep only a line in memory, because this is not
very hard and users will want to be able to operate on input files that
are bigger than will fit in memory all at once.

   If your program creates complicated data structures, just make them
in memory and give a fatal error if `malloc' returns zero.


File: standards.info,  Node: File Usage,  Prev: Memory Usage,  Up: Program Behavior

4.11 File Usage
===============

Programs should be prepared to operate when `/usr' and `/etc' are
read-only file systems.  Thus, if the program manages log files, lock
files, backup files, score files, or any other files which are modified
for internal purposes, these files should not be stored in `/usr' or
`/etc'.

   There are two exceptions.  `/etc' is used to store system
configuration information; it is reasonable for a program to modify
files in `/etc' when its job is to update the system configuration.
Also, if the user explicitly asks to modify one file in a directory, it
is reasonable for the program to store other files in the same
directory.


File: standards.info,  Node: Writing C,  Next: Documentation,  Prev: Program Behavior,  Up: Top

5 Making The Best Use of C
**************************

This chapter provides advice on how best to use the C language when
writing GNU software.

* Menu:

* Formatting::                  Formatting your source code.
* Comments::                    Commenting your work.
* Syntactic Conventions::       Clean use of C constructs.
* Names::                       Naming variables, functions, and files.
* System Portability::          Portability among different operating systems.
* CPU Portability::             Supporting the range of CPU types.
* System Functions::            Portability and ``standard'' library functions.
* Internationalization::        Techniques for internationalization.
* Character Set::               Use ASCII by default.
* Quote Characters::            Use `...' in the C locale.
* Mmap::                        How you can safely use `mmap'.


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

5.1 Formatting Your Source Code
===============================

It is important to put the open-brace that starts the body of a C
function in column one, so that they will start a defun.  Several tools
look for open-braces in column one to find the beginnings of C
functions.  These tools will not work on code not formatted that way.

   Avoid putting open-brace, open-parenthesis or open-bracket in column
one when they are inside a function, so that they won't start a defun.
The open-brace that starts a `struct' body can go in column one if you
find it useful to treat that definition as a defun.

   It is also important for function definitions to start the name of
the function in column one.  This helps people to search for function
definitions, and may also help certain tools recognize them.  Thus,
using Standard C syntax, the format is this:

     static char *
     concat (char *s1, char *s2)
     {
       ...
     }

or, if you want to use traditional C syntax, format the definition like
this:

     static char *
     concat (s1, s2)        /* Name starts in column one here */
          char *s1, *s2;
     {                     /* Open brace in column one here */
       ...
     }

   In Standard C, if the arguments don't fit nicely on one line, split
it like this:

     int
     lots_of_args (int an_integer, long a_long, short a_short,
                   double a_double, float a_float)
     ...

   The rest of this section gives our recommendations for other aspects
of C formatting style, which is also the default style of the `indent'
program in version 1.2 and newer.  It corresponds to the options

     -nbad -bap -nbc -bbo -bl -bli2 -bls -ncdb -nce -cp1 -cs -di2
     -ndj -nfc1 -nfca -hnl -i2 -ip5 -lp -pcs -psl -nsc -nsob

   We don't think of these recommendations as requirements, because it
causes no problems for users if two different programs have different
formatting styles.

   But whatever style you use, please use it consistently, since a
mixture of styles within one program tends to look ugly.  If you are
contributing changes to an existing program, please follow the style of
that program.

   For the body of the function, our recommended style looks like this:

     if (x < foo (y, z))
       haha = bar[4] + 5;
     else
       {
         while (z)
           {
             haha += foo (z, z);
             z--;
           }
         return ++x + bar ();
       }

   We find it easier to read a program when it has spaces before the
open-parentheses and after the commas.  Especially after the commas.

   When you split an expression into multiple lines, split it before an
operator, not after one.  Here is the right way:

     if (foo_this_is_long && bar > win (x, y, z)
         && remaining_condition)

   Try to avoid having two operators of different precedence at the same
level of indentation.  For example, don't write this:

     mode = (inmode[j] == VOIDmode
             || GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j])
             ? outmode[j] : inmode[j]);

   Instead, use extra parentheses so that the indentation shows the
nesting:

     mode = ((inmode[j] == VOIDmode
              || (GET_MODE_SIZE (outmode[j]) > GET_MODE_SIZE (inmode[j])))
             ? outmode[j] : inmode[j]);

   Insert extra parentheses so that Emacs will indent the code properly.
For example, the following indentation looks nice if you do it by hand,

     v = rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000
         + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000;

but Emacs would alter it.  Adding a set of parentheses produces
something that looks equally nice, and which Emacs will preserve:

     v = (rup->ru_utime.tv_sec*1000 + rup->ru_utime.tv_usec/1000
          + rup->ru_stime.tv_sec*1000 + rup->ru_stime.tv_usec/1000);

   Format do-while statements like this:

     do
       {
         a = foo (a);
       }
     while (a > 0);

   Please use formfeed characters (control-L) to divide the program into
pages at logical places (but not within a function).  It does not matter
just how long the pages are, since they do not have to fit on a printed
page.  The formfeeds should appear alone on lines by themselves.


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

5.2 Commenting Your Work
========================

Every program should start with a comment saying briefly what it is for.
Example: `fmt - filter for simple filling of text'.  This comment
should be at the top of the source file containing the `main' function
of the program.

   Also, please write a brief comment at the start of each source file,
with the file name and a line or two about the overall purpose of the
file.

   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 */


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

5.3 Clean Use of C Constructs
=============================

Please explicitly declare the types of all objects.  For example, you
should explicitly declare all arguments to functions, and you should
declare functions to return `int' rather than omitting the `int'.

   Some programmers like to use the GCC `-Wall' option, and change the
code whenever it issues a warning.  If you want to do this, then do.
Other programmers prefer not to use `-Wall', because it gives warnings
for valid and legitimate code which they do not want to change.  If you
want to do this, then do.  The compiler should be your servant, not
your master.

   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 to 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 (assignments inside
`while'-conditions are ok).  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

5.4 Naming Variables, Functions, and Files
==========================================

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.

   You might want to make sure that none of the file names would
conflict if the files were loaded onto an MS-DOS file system which
shortens the names.  You can use the program `doschk' to test for this.

   Some GNU programs were designed to limit themselves to file names of
14 characters or less, to avoid file name conflicts if they are read
into older System V systems.  Please preserve this feature in the
existing GNU programs that have it, but there is no need to do this in
new GNU programs.  `doschk' also reports file names longer than 14
characters.


File: standards.info,  Node: System Portability,  Next: CPU Portability,  Prev: Names,  Up: Writing C

5.5 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.  So
the kinds of portability that are absolutely necessary are quite
limited.  But it is important to support Linux-based GNU systems, since
they are the form of GNU that is popular.

   Beyond that, it is good to support the other free operating systems
(*BSD), and it is nice to support other Unix-like systems if you want
to.  Supporting a variety of Unix-like systems is desirable, although
not paramount.  It is usually not too hard, so you may as well do it.
But you don't have to consider it an obligation, if it does turn out to
be hard.

   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, VMS,
MVS, and older Macintosh systems, 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.

   If you do support Windows, please do not abbreviate it as "win".  In
hacker terminology, calling something a "win" is a form of praise.
You're free to praise Microsoft Windows on your own if you want, but
please don't do this in GNU packages.  Instead of abbreviating
"Windows" to "win", you can write it in full or abbreviate it to "woe"
or "w".  In GNU Emacs, for instance, we use `w32' in file names of
Windows-specific files, but the macro for Windows conditionals is
called `WINDOWSNT'.

   It is a good idea to define the "feature test macro" `_GNU_SOURCE'
when compiling your C files.  When you compile on GNU or GNU/Linux,
this will enable the declarations of GNU library extension functions,
and that will usually give you a compiler error message if you define
the same function names in some other way in your program.  (You don't
have to actually _use_ these functions, if you prefer to make the
program more portable to other systems.)

   But whether or not you use these GNU extensions, you should avoid
using their names for any other meanings.  Doing so would make it hard
to move your code into other GNU programs.


File: standards.info,  Node: CPU Portability,  Next: System Functions,