standards.texi

早期freebsd实现

int ignore_space_change_flag;
@end example

When you want to define names with constant integer values, use
@code{enum} rather than @samp{#define}.  GDB knows about enumeration
constants.

Use file names of 14 characters or less, to avoid creating gratuitous
problems on System V.


@node Using Extensions
@chapter 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'' @code{INLINE}
and define that as a macro to expand into either @code{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.  Such programs would
be broken by use of GNU extensions.

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 no good.

Since most computer systems do not yet implement @sc{ANSI} C, using the
@sc{ANSI} C features is effectively using a GNU extension, so the
same considerations apply.  (Except for @sc{ANSI} features that we
discourage, such as trigraphs---don't ever use them.)

@node Semantics
@chapter Program Behaviour for All Programs

Avoid arbitrary limits on the length or number of @emph{any} data
structure, including filenames, 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 @emph{including those with codes above 0177}.  The
only sensible exceptions would be utilities specifically intended for
interface to certain types of printers that can't handle those characters.

Check every system call for an error return, unless you know you wish to
ignore errors.  Include the system error text (from @code{perror} or
equivalent) in @emph{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 @code{malloc} or @code{realloc} to see if it
returned zero.  Check @code{realloc} even if you are making the block
smaller; in a system that rounds block sizes to a power of 2,
@code{realloc} may get a different block if you ask for less space.

In Unix, @code{realloc} can destroy the storage block if it returns
zero.  GNU @code{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 @code{malloc}.

You must expect @code{free} to alter the contents of the block that was
freed.  Anything you want to fetch from the block, you must fetch before
calling @code{free}.

Use @code{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 @code{readdir} or some other high-level interface.
These will be supported compatibly by GNU.

By default, the GNU system will provide the signal handling functions of
@sc{BSD} and of @sc{POSIX}.  So GNU software should be written to use
these.

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.


@node Errors
@chapter Formatting Error Messages

Error messages from compilers should look like this:

@example
@var{source-file-name}:@var{lineno}: @var{message}
@end example

Error messages from other noninteractive programs should look like this:

@example
@var{program}:@var{source-file-name}:@var{lineno}: @var{message}
@end example

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

@example
@var{program}: @var{message}
@end example

@noindent
when there is no relevant source file.

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 @var{message} should not begin with a capital letter when
it follows a program name and/or filename.  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.


@node Libraries
@chapter Library Behaviour

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 @code{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 @samp{_}.  They should also contain
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.


@node Portability
@chapter Portability As It Applies to GNU

Much of what is called ``portability'' in the Unix world refers to
porting to different Unix versions.  This is a secondary consideration
for GNU software, because its primary purpose is to run on top of one
and only one kernel, the GNU kernel, compiled with one and only one C
compiler, the GNU C compiler.  The amount and kinds of variation among
GNU systems on different cpu's will be like the variation among Berkeley
4.3 systems on different cpu's.

All users today run GNU software on non-GNU systems.  So supporting a
variety of non-GNU systems is desirable; simply not paramount.
The easiest way to achieve portability to a reasonable range of systems
is to use Autoconf.  It's unlikely that your program needs to know more
information about the host machine than Autoconf can provide, simply
because most of the programs that need such knowledge have already been
written.

It is difficult to be sure exactly what facilities the GNU kernel
will provide, since it isn't finished yet.  Therefore, assume you can
use anything in 4.3; just avoid using the format of semi-internal data
bases (e.g., directories) when there is a higher-level alternative
(readdir).

You can freely assume any reasonably standard facilities in the C
language, libraries or kernel, because we will find it necessary to
support these facilities in the full GNU system, whether or not we
have already done so.  The fact that there may exist kernels or C
compilers that lack these facilities is irrelevant as long as the GNU
kernel and C compiler support them.

It remains necessary to worry about differences among cpu types, such
as the difference in byte ordering and alignment restrictions.  It's
unlikely that 16-bit machines will ever be supported by GNU, so there
is no point in spending any time to consider the possibility that an
int will be less than 32 bits.

You can assume that all pointers have the same format, regardless
of the type they point to, and that this is really an integer.
There are some weird machines where this isn't true, but they aren't
important; don't waste time catering to them.  Besides, eventually
we will put function prototypes into all GNU programs, and that will
probably make your program work even on weird machines.

Since some important machines (including the 68000) are big-endian,
it is important not to assume that the address of an int object
is also the address of its least-significant byte.  Thus, don't
make the following mistake:

@example
int c;
@dots{}
while ((c = getchar()) != EOF)
        write(file_descriptor, &c, 1);
@end example

You can assume that it is reasonable to use a meg of memory.  Don't
strain to reduce memory usage unless it can get to that level.  If
your program creates complicated data structures, just make them in
core and give a fatal error if malloc returns zero.

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 core all at once.


@node User Interfaces
@chapter Standards for Command Line Interfaces

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.

It is a good idea to follow the @sc{POSIX} guidelines for the
command-line options of a program.  The easiest way to do this is to use
@code{getopt} to parse them.  Note that the GNU version of @code{getopt}
will normally permit options anywhere among the arguments unless the
special argument @samp{--} is used.  This is not what @sc{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
@code{getopt_long}.

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 @samp{-o}).  Even if you allow an output file name
as an ordinary argument for compatibility, try to provide a suitable
option as well.  This will lead to more consistency among GNU
utilities, so that there are fewer idiosyncracies for users to
remember.

Programs should support an option @samp{--version} which prints the
program's version number, and an option @samp{--help} which prints
option usage information.


@node Documentation
@chapter Documenting Programs

Please use Texinfo for documenting GNU programs.  See the Texinfo
manual, either the hardcopy or the version in the GNU Emacs Info
subsystem (@kbd{C-h i}).  See existing GNU Texinfo files (e.g. those
under the @file{man/} directory in the GNU Emacs Distribution) for
examples.

The title page of the manual should state the version of the program
which the manual applies to.  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.

The manual should document all command-line arguments and all
commands.  It should give examples of their use.  But don't organize
the manual as a list of features.  Instead, organize it by the
concepts a user will have before reaching that point in the manual.
Address the goals that a user will have in mind, and explain how to
accomplish them.

In addition to its manual, the package should have a file named
@file{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.
This way, a user upgrading from any previous version can see what
is new.

@node Releases
@chapter Making Releases

Package the distribution of Foo version 69.96 in a tar file named
@file{foo-69.96.tar}.  It should unpack into a subdirectory named
@file{foo-69.96}.

Building and installing the program should never modify any of the files
contained in the distribution.  This means that all the files that form
part of the program in any way must be classified into @dfn{source
files} and @dfn{non-source files}.  Source files are written by humans
and never changed automatically; non-source files are produced from
source files by programs under the control of the Makefile.

Naturally, all the source files must be in the distribution.  It is okay
to include non-source files in the distribution, provided they are
up-to-date and machine-independent, so that building the distribution
normally will never modify them.  We commonly included non-source files
produced by Bison, Lex, @TeX{}, and Makeinfo; this helps avoid
unnecessary dependencies between our distributions, so that users can
install whichever packages they want to install.

Non-source files that might actually be modified by building and
installing the program should @strong{never} be included in the
distribution.  So if you do distribute non-source files, always make
sure they are up to date when you make a new distribution.

Make sure that no file name in the distribution is no more than 14
characters long.  Nowadays, there are systems that adhere to a foolish
interpretation of the POSIX standard which holds that they should refuse
to open a longer name, rather than truncating as they did in the past.

Try to make sure that all the file names will be unique on MS-DOG.  A
name on MS-DOG consists of up to 8 characters, optionally followed by a
period and up to three characters.  MS-DOG will truncate extra
characters both before and after the period.  Thus,
@file{foobarhacker.c} and @file{foobarhacker.o} are not ambiguous; they
are truncated to @file{foobarha.c} and @file{foobarha.o}, which are
distinct.

Include in your distribution a copy of the @file{texinfo.tex} you used
to test print any @file{*.texinfo} files.

Likewise, if your program uses small GNU software packages like regex,
getopt, obstack, or termcap, include them in the distribution file.
Leaving them out would make the distribution file a little smaller at
the expense of possible inconvenience to a user who doesn't know what
other files to get.
@bye