autoconf.texi

这是一个自动生成MAKEFILE的工具。在LINUX工程项目里是很好的帮手。希望对大家有点帮助。

Alternately, if your code tests for configuration options using
@code{#ifdef} instead of @code{#if}, a default value can be to
@code{#undef} the variable instead of to define it to a value.  On
systems that have @file{unistd.h}, @code{configure} will change the
second line to read @samp{#define HAVE_UNISTD_H 1}.  On other systems,
it will comment that line out (in case the system predefines that
symbol).

@example
@group
/* Define if you have unistd.h.  */
#undef HAVE_UNISTD_H
@end group
@end example

@node Invoking autoheader,  , Header Templates, Configuration Headers
@subsection Using @code{autoheader} to Create @file{config.h.in}

The @code{autoheader} program can create a template file of C
@samp{#define} statements for @code{configure} to use.  If
@file{configure.in} invokes @code{AC_CONFIG_HEADER(@var{file})},
@code{autoheader} creates @file{@var{file}.in}; if multiple file
arguments are given, the first one is used.  Otherwise,
@code{autoheader} creates @file{config.h.in}.

If you give @code{autoheader} an argument, it uses that file instead of
@file{configure.in} and writes the header file to the standard output
instead of to @file{config.h.in}.  If you give @code{autoheader} an
argument of @samp{-}, it reads the standard input instead of
@file{configure.in} and writes the header file to the standard output.

@code{autoheader} scans @file{configure.in} and figures out which C
preprocessor symbols it might define.  It copies comments and
@code{#define} and @code{#undef} statements from a file called
@file{acconfig.h}, which comes with and is installed with Autoconf.  It
also uses a file called @file{acconfig.h} in the current directory, if
present.  If you @code{AC_DEFINE} any additional symbols, you must
create that file with entries for them.  For symbols defined by
@code{AC_CHECK_HEADERS}, @code{AC_CHECK_FUNCS}, @code{AC_CHECK_SIZEOF},
or @code{AC_CHECK_LIB}, @code{autoheader} generates comments and
@code{#undef} statements itself rather than copying them from a file,
since the possible symbols are effectively limitless.

The file that @code{autoheader} creates contains mainly @code{#define}
and @code{#undef} statements and their accompanying comments.  If
@file{./acconfig.h} contains the string @samp{@@TOP@@},
@code{autoheader} copies the lines before the line containing
@samp{@@TOP@@} into the top of the file that it generates.  Similarly,
if @file{./acconfig.h} contains the string @samp{@@BOTTOM@@},
@code{autoheader} copies the lines after that line to the end of the
file it generates.  Either or both of those strings may be omitted.

An alternate way to produce the same effect is to create the files
@file{@var{file}.top} (typically @file{config.h.top}) and/or
@file{@var{file}.bot} in the current directory.  If they exist,
@code{autoheader} copies them to the beginning and end, respectively, of
its output.  Their use is discouraged because they have file names that
contain two periods, and so can not be stored on MS-DOS; also, they are
two more files to clutter up the directory.  But if you use the
@samp{--localdir=@var{dir}} option to use an @file{acconfig.h} in another
directory, they give you a way to put custom boilerplate in each
individual @file{config.h.in}.

@code{autoheader} accepts the following options:

@table @code
@item --help
@itemx -h
Print a summary of the command line options and exit.

@item --localdir=@var{dir}
@itemx -l @var{dir}
Look for the package files @file{aclocal.m4} and @file{acconfig.h} (but
not @file{@var{file}.top} and @file{@var{file}.bot}) in directory
@var{dir} instead of in the current directory.

@item --macrodir=@var{dir}
@itemx -m @var{dir}
@evindex AC_MACRODIR
Look for the installed macro files and @file{acconfig.h} in directory
@var{dir}.  You can also set the @code{AC_MACRODIR} environment variable
to a directory; this option overrides the environment variable.

@item --version
Print the version number of Autoconf and exit.
@end table

@node Subdirectories, Default Prefix, Configuration Headers, Setup
@section Configuring Other Packages in Subdirectories

In most situations, calling @code{AC_OUTPUT} is sufficient to produce
@file{Makefile}s in subdirectories.  However, @code{configure} scripts
that control more than one independent package can use
@code{AC_CONFIG_SUBDIRS} to run @code{configure} scripts for other
packages in subdirectories.

@defmac AC_CONFIG_SUBDIRS (@var{dir} @dots{})
@maindex CONFIG_SUBDIRS
@ovindex subdirs
Make @code{AC_OUTPUT} run @code{configure} in each subdirectory
@var{dir} in the given whitespace-separated list.  If a given @var{dir}
is not found, no error is reported, so a @code{configure} script can
configure whichever parts of a large source tree are present.  If a
given @var{dir} contains @file{configure.in} but no @code{configure},
the Cygnus @code{configure} script found by @code{AC_CONFIG_AUXDIR} is
used.

The subdirectory @code{configure} scripts are given the same
command line options that were given to this @code{configure} script,
with minor changes if needed (e.g., to adjust a relative path for the
cache file or source directory).  This macro also sets the output
variable @code{subdirs} to the list of directories @samp{@var{dir}
@dots{}}.  @file{Makefile} rules can use this variable to determine
which subdirectories to recurse into.  This macro may be called multiple
times.
@end defmac

@node Default Prefix, Versions, Subdirectories, Setup
@section Default Prefix

By default, @code{configure} sets the prefix for files it installs to
@file{/usr/local}.  The user of @code{configure} can select a different
prefix using the @samp{--prefix} and @samp{--exec-prefix} options.
There are two ways to change the default: when creating
@code{configure}, and when running it.

Some software packages might want to install in a directory besides
@file{/usr/local} by default.  To accomplish that, use the
@code{AC_PREFIX_DEFAULT} macro.

@defmac AC_PREFIX_DEFAULT (@var{prefix})
Set the default installation prefix to @var{prefix} instead of @file{/usr/local}.
@end defmac

It may be convenient for users to have @code{configure} guess the
installation prefix from the location of a related program that they
have already installed.  If you wish to do that, you can call
@code{AC_PREFIX_PROGRAM}.

@defmac AC_PREFIX_PROGRAM (@var{program})
@maindex PREFIX_PROGRAM
If the user did not specify an installation prefix (using the
@samp{--prefix} option), guess a value for it by looking for
@var{program} in @code{PATH}, the way the shell does.  If @var{program}
is found, set the prefix to the parent of the directory containing
@var{program}; otherwise leave the prefix specified in
@file{Makefile.in} unchanged.  For example, if @var{program} is
@code{gcc} and the @code{PATH} contains @file{/usr/local/gnu/bin/gcc},
set the prefix to @file{/usr/local/gnu}.
@end defmac

@node Versions,  , Default Prefix, Setup
@section Version Numbers in @code{configure}

The following macros manage version numbers for @code{configure}
scripts.  Using them is optional.

@defmac AC_PREREQ (@var{version})
@maindex PREREQ
Ensure that a recent enough version of Autoconf is being used.  If the
version of Autoconf being used to create @code{configure} is earlier
than @var{version}, print an error message on the standard error output
and do not create @code{configure}.  For example:

@example
AC_PREREQ(1.8)
@end example

This macro is useful if your @file{configure.in} relies on non-obvious
behavior that changed between Autoconf releases.  If it merely needs
recently added macros, then @code{AC_PREREQ} is less useful, because the
@code{autoconf} program already tells the user which macros are not
found.  The same thing happens if @file{configure.in} is processed by a
version of Autoconf older than when @code{AC_PREREQ} was added.
@end defmac

@defmac AC_REVISION (@var{revision-info})
@maindex REVISION
Copy revision stamp @var{revision-info} into the @code{configure}
script, with any dollar signs or double-quotes removed.  This macro lets
you put a revision stamp from @file{configure.in} into @code{configure}
without RCS or CVS changing it when you check in @code{configure}.  That
way, you can determine easily which revision of @file{configure.in} a
particular @code{configure} corresponds to.

It is a good idea to call this macro before @code{AC_INIT} so that the
revision number is near the top of both @file{configure.in} and
@code{configure}.  To support doing that, the @code{AC_REVISION} output
begins with @samp{#! /bin/sh}, like the normal start of a
@code{configure} script does.

For example, this line in @file{configure.in}:

@c The asis prevents RCS from changing the example in the manual.
@example
AC_REVISION($@asis{Revision: 1.30 }$)dnl
@end example

@noindent
produces this in @code{configure}:

@example
#! /bin/sh
# From configure.in Revision: 1.30
@end example
@end defmac

@node Existing Tests, Writing Tests, Setup, Top
@chapter Existing Tests

These macros test for particular system features that packages
might need or want to use.  If you need to test for a kind of feature
that none of these macros check for, you can probably do it by calling
primitive test macros with appropriate arguments (@pxref{Writing Tests}).

These tests print messages telling the user which feature they're
checking for, and what they find.  They cache their results for future
@code{configure} runs (@pxref{Caching Results}).

Some of these macros set output variables.  @xref{Makefile
Substitutions}, for how to get their values.  The phrase ``define
@var{name}'' is used below as a shorthand to mean ``define C
preprocessor symbol @var{name} to the value 1''.  @xref{Defining
Symbols}, for how to get those symbol definitions into your program.

@menu
* Alternative Programs::        Selecting between alternative programs.
* Libraries::                   Library archives that might be missing.
* Library Functions::           C library functions that might be missing.
* Header Files::                Header files that might be missing.
* Structures::                  Structures or members that might be missing.
* Typedefs::                    @code{typedef}s that might be missing.
* C Compiler Characteristics::  
* Fortran 77 Compiler Characteristics::  
* System Services::             Operating system services.
* UNIX Variants::               Special kludges for specific UNIX variants.
@end menu

@node Alternative Programs, Libraries, Existing Tests, Existing Tests
@section Alternative Programs

These macros check for the presence or behavior of particular programs.
They are used to choose between several alternative programs and to
decide what to do once one has been chosen.
If there is no macro specifically defined to check for a program you need,
and you don't need to check for any special properties of
it, then you can use one of the general program check macros.

@menu
* Particular Programs::         Special handling to find certain programs.
* Generic Programs::            How to find other programs.
@end menu

@node Particular Programs, Generic Programs, Alternative Programs, Alternative Programs
@subsection Particular Program Checks

These macros check for particular programs---whether they exist, and
in some cases whether they support certain features.

@defmac AC_DECL_YYTEXT
@maindex DECL_YYTEXT
@cvindex YYTEXT_POINTER
@ovindex LEX_OUTPUT_ROOT
Define @code{YYTEXT_POINTER} if @code{yytext} is a @samp{char *} instead
of a @samp{char []}.  Also set output variable @code{LEX_OUTPUT_ROOT} to
the base of the file name that the lexer generates; usually
@file{lex.yy}, but sometimes something else.  These results vary
according to whether @code{lex} or @code{flex} is being used.
@end defmac

@defmac AC_PROG_AWK
@maindex PROG_AWK
@ovindex AWK
Check for @code{mawk}, @code{gawk}, @code{nawk}, and @code{awk}, in that
order, and set output variable @code{AWK} to the first one that it
finds.  It tries @code{mawk} first because that is reported to be the
fastest implementation.
@end defmac

@defmac AC_PROG_CC
@maindex PROG_CC
@ovindex CC
@ovindex CFLAGS
Determine a C compiler to use.  If @code{CC} is not already set in the
environment, check for @code{gcc}, and use @code{cc} if that's not found.
Set output variable @code{CC} to the name of the compiler found.

If using the GNU C compiler, set shell variable @code{GCC} to
@samp{yes}, empty otherwise.  If output variable @code{CFLAGS} was
not already set, set it to @samp{-g -O2} for the GNU C compiler
(@samp{-O2} on systems where GCC does not accept @samp{-g}), or @samp{-g}
for other compilers.

If the C compiler being used does not produce executables that can run
on the system where @code{configure} is being run, set the shell
variable @code{cross_compiling} to @samp{yes}, otherwise @samp{no}.
In other words, this tests whether the build system type is different
from the host system type (the target system type is irrelevant to this
test).  @xref{Manual Configuration}, for more on support for cross compiling.
@end defmac

@defmac AC_PROG_CC_C_O
@maindex PROG_CC_C_O
@cvindex NO_MINUS_C_MINUS_O
If the C compiler does not accept the @samp{-c} and @samp{-o} options
simultaneously, define @code{NO_MINUS_C_MINUS_O}.
@end defmac

@defmac AC_PROG_CPP
@maindex PROG_CPP
@ovindex CPP
Set output variable @code{CPP} to a command that runs the
C preprocessor.  If @samp{$CC -E} doesn't