configure Scripts
configure Scripts
A physicist, an engineer, and a computer scientist were discussing the nature of God. Surely a Physicist, said the physicist, because early in the Creation, God made Light; and you know, Maxwell's equations, the dual nature of electro-magnetic waves, the relativist consequences... An Engineer!, said the engineer, because before making Light, God split the Chaos into Land and Water; it takes a hell of an engineer to handle that big amount of mud, and orderly separation of solids from liquids... The computer scientist shouted: And the Chaos, where do you think it was coming from, hmm? ---Anonymous
Autoconf is a tool for producing shell scripts that automatically configure software source code packages to adapt to many kinds of UNIX-like systems. The configuration scripts produced by Autoconf are independent of Autoconf when they are run, so their users do not need to have Autoconf.
The configuration scripts produced by Autoconf require no manual user intervention when run; they do not normally even need an argument specifying the system type. Instead, they test for the presence of each feature that the software package they are for might need individually. (Before each check, they print a one-line message stating what they are checking for, so the user doesn't get too bored while waiting for the script to finish.) As a result, they deal well with systems that are hybrids or customized from the more common UNIX variants. There is no need to maintain files that list the features supported by each release of each variant of UNIX.
For each software package that Autoconf is used with, it creates a configuration script from a template file that lists the system features that the package needs or can use. After the shell code to recognize and respond to a system feature has been written, Autoconf allows it to be shared by many software packages that can use (or need) that feature. If it later turns out that the shell code needs adjustment for some reason, it needs to be changed in only one place; all of the configuration scripts can be regenerated automatically to take advantage of the updated code.
The Metaconfig package is similar in purpose to Autoconf, but the scripts it produces require manual user intervention, which is quite inconvenient when configuring large source trees. Unlike Metaconfig scripts, Autoconf scripts can support cross-compiling, if some care is taken in writing them.
There are several jobs related to making portable software packages that Autoconf currently does not do. Among these are automatically creating `Makefile' files with all of the standard targets, and supplying replacements for standard library functions and header files on systems that lack them. Work is in progress to add those features in the future.
Autoconf imposes some restrictions on the names of macros used with
#ifdef in C programs (see section Preprocessor Symbol Index).
Autoconf requires GNU m4 in order to generate the scripts. It
uses features that some UNIX versions of m4 do not have. It also
overflows internal limits of some versions of m4, including GNU
m4 1.0. You must use version 1.1 or later of GNU m4.
Using version 1.3 or later will be much faster than 1.1 or 1.2.
See section Upgrading From Version 1, for information about upgrading from version 1. See section History of Autoconf, for the story of Autoconf's development. See section Questions About Autoconf, for answers to some common questions about Autoconf.
Mail suggestions and bug reports for Autoconf to
bug-gnu-utils@prep.ai.mit.edu. Please include the Autoconf version
number, which you can get by running `autoconf --version'.
configure Scripts
The configuration scripts that Autoconf produces are by convention
called configure. When run, configure creates several
files, replacing configuration parameters in them with appropriate
values. The files that configure creates are:
#define directives (see section Configuration Header Files);
configure makes a mistake.
To create a configure script with Autoconf, you need to write an
Autoconf input file `configure.in' and run autoconf on it.
If you write your own feature tests to supplement those that come with
Autoconf, you might also write files called `aclocal.m4' and
`acsite.m4'. If you use a C header file to contain #define
directives, you might also write `acconfig.h', and you will
distribute the Autoconf-generated file `config.h.in' with the
package.
Here is a diagram showing how the files that can be used in
configuration are produced. Programs that are executed are suffixed by
`*'. Optional files are enclosed in square brackets (`[]').
autoconf and autoheader also read the installed Autoconf
macro files (by reading `autoconf.m4').
Files used in preparing a software package for distribution:
your source files --> [autoscan*] --> [configure.scan] --> configure.in
configure.in --. .------> autoconf* -----> configure
+---+
[aclocal.m4] --+ `---.
[acsite.m4] ---' |
+--> [autoheader*] -> [config.h.in]
[acconfig.h] ----. |
+-----'
[config.h.top] --+
[config.h.bot] --'
Makefile.in -------------------------------> Makefile.in
Files used in configuring a software package:
.-------------> config.cache
configure* ------------+-------------> config.log
|
[config.h.in] -. v .-> [config.h] -.
+--> config.status* -+ +--> make*
Makefile.in ---' `-> Makefile ---'
To produce a configure script for a software package, create a
file called `configure.in' that contains invocations of the
Autoconf macros that test the system features your package needs or can
use. Autoconf macros already exist to check for many features; see
section Existing Tests, for their descriptions. For most other
features, you can use Autoconf template macros to produce custom checks;
see section Writing Tests, for information about them. For especially
tricky or specialized features, `configure.in' might need to
contain some hand-crafted shell commands. The autoscan
program can give you a good start in writing `configure.in'
(see section Using autoscan to Create `configure.in', for more information).
The order in which `configure.in' calls the Autoconf macros
is not important, with a few exceptions. Every
`configure.in' must contain a call to AC_INIT before
the checks, and a call to AC_OUTPUT at the end
(see section Creating Output Files). Additionally, some macros rely on other macros
having been called first, because they check previously set
values of some variables to decide what to do. These macros are
noted in the individual descriptions (see section Existing Tests),
and they also warn you when creating configure if they are
called out of order.
To encourage consistency, here is a suggested order for calling the Autoconf macros. Generally speaking, the things near the end of this list could depend on things earlier in it. For example, library functions could be affected by typedefs and libraries.
AC_INIT(file)checks for programs checks for libraries checks for header files checks for typedefs checks for structures checks for compiler characteristics checks for library functions checks for system servicesAC_OUTPUT([file...])
It is best to put each macro call on its own line in
`configure.in'. Most of the macros don't add extra newlines; they
rely on the newline after the macro call to terminate the commands.
This approach makes the generated configure script a little
easier to read by not inserting lots of blank lines. It is generally
safe to set shell variables on the same line as a macro call, because
the shell allows assignments without intervening newlines.
When calling macros that take arguments, there must not be any blank
space between the macro name and the open parenthesis. Arguments can be
more than one line long if they are enclosed within the m4 quote
characters `[' and `]'. If you have a long line such as a
list of file names, you can generally use a backslash at the end of a
line to continue it logically on the next line (this is implemented by
the shell, not by anything special that Autoconf does).
Some macros handle two cases: what to do if the given condition is met, and what to do if the condition is not met. In some places you might want to do something if a condition is true but do nothing if it's false, or vice versa. To omit the true case, pass an empty value for the action-if-found argument to the macro. To omit the false case, omit the action-if-not-found argument to the macro, including the comma before it.
You can include comments in `configure.in' files by starting them
with the m4 builtin macro dnl, which discards text up
through the next newline. These comments do not appear in the generated
configure scripts. For example, it is helpful to begin
`configure.in' files with a line like this:
dnl Process this file with autoconf to produce a configure script.
autoscan to Create `configure.in'
The autoscan program can help you create a `configure.in'
file for a software package. autoscan examines source files in
the directory tree rooted at a directory given as a command line
argument, or the current directory if none is given. It searches the
source files for common portability problems and creates a file
`configure.scan' which is a preliminary `configure.in' for
that package.
You should manually examine `configure.scan' before renaming it to
`configure.in'; it will probably need some adjustments.
Occasionally autoscan outputs a macro in the wrong order relative
to another macro, so that autoconf produces a warning; you need
to move such macros manually. Also, if you want the package to use a
configuration header file, you must add a call to
AC_CONFIG_HEADER (see section Configuration Header Files). You might also
have to change or add some #if directives to your program in
order to make it work with Autoconf (see section Using ifnames to List Conditionals, for
information about a program that can help with that job).
autoscan uses several data files, which are installed along with the
distributed Autoconf macro files, to determine which macros to output
when it finds particular symbols in a package's source files. These
files all have the same format. Each line consists of a symbol,
whitespace, and the Autoconf macro to output if that symbol is
encountered. Lines starting with `#' are comments.
autoscan is only installed if you already have Perl installed.
autoscan accepts the following options:
--help
--macrodir=dir
AC_MACRODIR
environment variable to a directory; this option overrides the
environment variable.
--verbose
--version
ifnames to List Conditionals
ifnames can help when writing a `configure.in' for a
software package. It prints the identifiers that the package already
uses in C preprocessor conditionals. If a package has already been set
up to have some portability, this program can help you figure out what
its configure needs to check for. It may help fill in some gaps
in a `configure.in' generated by autoscan (see section Using autoscan to Create `configure.in').
ifnames scans all of the C source files named on the command line
(or the standard input, if none are given) and writes to the standard
output a sorted list of all the identifiers that appear in those files
in #if, #elif, #ifdef, or #ifndef
directives. It prints each identifier on a line, followed by a
space-separated list of the files in which that identifier occurs.
ifnames accepts the following options:
--help
-h
--macrodir=dir
-m dir
AC_MACRODIR
environment variable to a directory; this option overrides the
environment variable.
--version
autoconf to Create configure
To create configure from `configure.in', run the
autoconf program with no arguments. autoconf processes
`configure.in' with the m4 macro processor, using the
Autoconf macros. If you give autoconf an argument, it reads that
file instead of `configure.in' and writes the configuration script
to the standard output instead of to configure. If you give
autoconf the argument `-', it reads the standard input
instead of `configure.in' and writes the configuration script on
the standard output.
The Autoconf macros are defined in several files. Some of the files are
distributed with Autoconf; autoconf reads them first. Then it
looks for the optional file `acsite.m4' in the directory that
contains the distributed Autoconf macro files, and for the optional file
`aclocal.m4' in the current directory. Those files can contain
your site's or the package's own Autoconf macro definitions
(see section Writing Macros, for more information). If a macro is defined
in more than one of the files that autoconf reads, the last
definition it reads overrides the earlier ones.
autoconf accepts the following options:
--help
-h
--localdir=dir
-l dir
--macrodir=dir
-m dir
AC_MACRODIR environment variable to a directory; this
option overrides the environment variable.
--version
autoreconf to Update configure Scripts
If you have a lot of Autoconf-generated configure scripts, the
autoreconf program can save you some work. It runs
autoconf (and autoheader, where appropriate) repeatedly to
remake the Autoconf configure scripts and configuration header
templates in the directory tree rooted at the current directory. By
default, it only remakes those files that are older than their
`configure.in' or (if present) `aclocal.m4'. Since
autoheader does not change the timestamp of its output file if
the file wouldn't be changing, this is not necessarily the minimum
amount of work. If you install a new version of Autoconf, you can make
autoreconf remake all of the files by giving it the
`--force' option.
If you give autoreconf the `--macrodir=dir' or
`--localdir=dir' options, it passes them down to
autoconf and autoheader (with relative paths adjusted
properly).
autoreconf does not support having, in the same directory tree,
both directories that are parts of a larger package (sharing
`aclocal.m4' and `acconfig.h'), and directories that are
independent packages (each with their own `aclocal.m4' and
`acconfig.h'). It assumes that they are all part of the same
package, if you use `--localdir', or that each directory is a
separate package, if you don't use it. This restriction may be removed
in the future.
See section Automatic Remaking, for `Makefile' rules to automatically
remake configure scripts when their source files change. That
method handles the timestamps of configuration header templates
properly, but does not pass `--macrodir=dir' or
`--localdir=dir'.
autoreconf accepts the following options:
--help
-h
--force
-f
--localdir=dir
-l dir
autoconf and autoheader look for the package files
`aclocal.m4' and (autoheader only) `acconfig.h' (but
not `file.top' and `file.bot') in directory
dir instead of in the directory containing each `configure.in'.
--macrodir=dir
-m dir
AC_MACRODIR
environment variable to a directory; this option overrides the
environment variable.
--verbose
autoreconf runs
autoconf (and autoheader, if appropriate).
--version
Autoconf-generated configure scripts need some information about
how to initialize, such as how to find the package's source files; and
about the output files to produce. The following sections describe
initialization and creating output files.
configure Input
Every configure script must call AC_INIT before doing
anything else. The only other required macro is AC_OUTPUT
(see section Creating Output Files).
configure checks for this file's existence to
make sure that the directory that it is told contains the source code in
fact does. Occasionally people accidentally specify the wrong directory
with `--srcdir'; this is a safety check. See section Running configure Scripts,
for more information.
Packages that do manual configuration or use the install program
might need to tell configure where to find some other shell
scripts by calling AC_CONFIG_AUX_DIR, though the default places
it looks are correct for most cases.
configure scripts that are in directory dir. These
are auxiliary files used in configuration. dir can be either
absolute or relative to `srcdir'. The default is
`srcdir' or `srcdir/..' or
`srcdir/../..', whichever is the first that contains
`install-sh'. The other files are not checked for, so that using
AC_PROG_INSTALL does not automatically require distributing the
other auxiliary files. It checks for `install.sh' also, but that
name is obsolete because some make programs have a rule that
creates `install' from it if there is no `Makefile'.
Every Autoconf-generated configure script must finish by calling
AC_OUTPUT. It is the macro that creates the `Makefile's and
optional other files resulting from configuration. The only other
required macro is AC_INIT (see section Finding configure Input).
If AC_CONFIG_HEADER, AC_LINK_FILES, or
AC_CONFIG_SUBDIRS has been called, this macro also creates the
files named as their arguments.
A typical call to AC_OUTPUT looks like this:
AC_OUTPUT(Makefile src/Makefile man/Makefile X/Imakefile)
You can override an input file name by appending to file a colon-separated list of input files. Examples:
AC_OUTPUT(Makefile:templates/top.mk lib/Makefile:templates/lib.mk) AC_OUTPUT(Makefile:templates/vars.mk:Makefile.in:templates/rules.mk)
Doing this allows you to keep your file names acceptable to MS-DOS, or to prepend and/or append boilerplate to the file.
If you pass extra-cmds, those commands will be inserted into
`config.status' to be run after all its other processing. If
init-cmds are given, they are inserted just before
extra-cmds, with shell variable, command, and backslash
substitutions performed on them in configure. You can use
init-cmds to pass variables from configure to the
extra-cmds. If AC_OUTPUT_COMMANDS has been called, the
commands given to it are run just before the commands passed to this macro.
configure. This macro may be called multiple times.
Here is an unrealistic example:
fubar=27 AC_OUTPUT_COMMANDS([echo this is extra $fubar, and so on.], fubar=$fubar) AC_OUTPUT_COMMANDS([echo this is another, extra, bit], [echo init bit])
If you run make on subdirectories, you should run it using the
make variable MAKE. Most versions of make set
MAKE to the name of the make program plus any options it
was given. (But many do not include in it the values of any variables
set on the command line, so those are not passed on automatically.)
Some old versions of make do not set this variable. The
following macro allows you to use it even with those versions.
make predefines the variable MAKE, define output
variable SET_MAKE to be empty. Otherwise, define SET_MAKE
to contain `MAKE=make'. Calls AC_SUBST for SET_MAKE.
To use this macro, place a line like this in each `Makefile.in'
that runs MAKE on other directories:
@SET_MAKE@
Each subdirectory in a distribution that contains something to be
compiled or installed should come with a file `Makefile.in', from
which configure will create a `Makefile' in that directory.
To create a `Makefile', configure performs a simple variable
substitution, replacing occurrences of `@variable@' in
`Makefile.in' with the value that configure has determined
for that variable. Variables that are substituted into output files in
this way are called output variables. They are ordinary shell
variables that are set in configure. To make configure
substitute a particular variable into the output files, the macro
AC_SUBST must be called with that variable name as an argument.
Any occurrences of `@variable@' for other variables are
left unchanged. See section Setting Output Variables, for more information on
creating output variables with AC_SUBST.
A software package that uses a configure script should be
distributed with a file `Makefile.in', but no `Makefile'; that
way, the user has to properly configure the package for the local system
before compiling it.
See section `Makefile Conventions' in The GNU Coding Standards, for more information on what to put in `Makefile's.
Some output variables are preset by the Autoconf macros. Some of the Autoconf macros set additional output variables, which are mentioned in the descriptions for those macros. See section Output Variable Index, for a complete list of output variables. Here is what each of the preset ones contains. See section `Variables for Installation Directories' in The GNU Coding Standards, for more information about the variables with names that end in `dir'.
configure and giving the name of the input file.
AC_OUTPUT adds a comment line containing this variable to the top
of every `Makefile' it creates. For other files, you should
reference this variable in a comment at the top of each input file. For
example, an input shell script should begin like this:
#! /bin/sh # @configure_input@
The presence of that line also reminds people editing the file that it
needs to be processed by configure in order to be used.
srcdir.
configure runs, the default value is set
when you call AC_PROG_CC (or empty if you don't). configure
uses this variable when compiling programs to test for C features.
configure runs, the default value is
empty. configure uses this variable when compiling or
preprocessing programs to test for C features.
configure runs, the default value is
set when you call AC_PROG_CXX (or empty if you don't).
configure uses this variable when compiling programs to test for
C++ features.
configure runs, the default
value is set when you call AC_PROG_F77 (or empty if you don't).
configure uses this variable when compiling programs to test for
Fortran 77 features.
AC_CONFIG_HEADER
is called, configure replaces `@DEFS@' with
`-DHAVE_CONFIG_H' instead (see section Configuration Header Files). This
variable is not defined while configure is performing its tests,
only when creating the output files. See section Setting Output Variables, for
how to check the results of previous tests.
configure runs,
the default value is empty. configure uses this variable when
linking programs to test for C features.
You can support compiling a software package for several architectures simultaneously from the same copy of the source code. The object files for each architecture are kept in their own directory.
To support doing this, make uses the VPATH variable to
find the files that are in the source directory. GNU make and
most other recent make programs can do this. Older make
programs do not support VPATH; when using them, the source code
must be in the same directory as the object files.
To support VPATH, each `Makefile.in' should contain two
lines that look like:
srcdir = @srcdir@ VPATH = @srcdir@
Do not set VPATH to the value of another variable, for example
`VPATH = $(srcdir)', because some versions of make do not do
variable substitutions on the value of VPATH.
configure substitutes in the correct value for srcdir when
it produces `Makefile'.
Do not use the make variable $<, which expands to the
pathname of the file in the source directory (found with VPATH),
except in implicit rules. (An implicit rule is one such as `.c.o',
which tells how to create a `.o' file from a `.c' file.) Some
versions of make do not set $< in explicit rules; they
expand it to an empty value.
Instead, `Makefile' command lines should always refer to source files by prefixing them with `$(srcdir)/'. For example:
time.info: time.texinfo
$(MAKEINFO) $(srcdir)/time.texinfo
You can put rules like the following in the top-level `Makefile.in' for a package to automatically update the configuration information when you change the configuration files. This example includes all of the optional files, such as `aclocal.m4' and those related to configuration header files. Omit from the `Makefile.in' rules any of these files that your package does not use.
The `${srcdir}/' prefix is included because of limitations in the
VPATH mechanism.
The `stamp-' files are necessary because the timestamps of
`config.h.in' and `config.h' will not be changed if remaking
them does not change their contents. This feature avoids unnecessary
recompilation. You should include the file `stamp-h.in' your
package's distribution, so make will consider `config.h.in'
up to date. On some old BSD systems, touch or any command that
results in an empty file does not update the timestamps, so use a
command like echo as a workaround.
${srcdir}/configure: configure.in aclocal.m4
cd ${srcdir} && autoconf
# autoheader might not change config.h.in, so touch a stamp file.
${srcdir}/config.h.in: stamp-h.in
${srcdir}/stamp-h.in: configure.in aclocal.m4 acconfig.h \
config.h.top config.h.bot
cd ${srcdir} && autoheader
echo timestamp > ${srcdir}/stamp-h.in
config.h: stamp-h
stamp-h: config.h.in config.status
./config.status
Makefile: Makefile.in config.status
./config.status
config.status: configure
./config.status --recheck
In addition, you should pass `echo timestamp > stamp-h' in the
extra-cmds argument to AC_OUTPUT, so `config.status'
will ensure that `config.h' is considered up to date.
See section Creating Output Files, for more information about AC_OUTPUT.
See section Recreating a Configuration, for more examples of handling configuration-related dependencies.
When a package tests more than a few C preprocessor symbols, the command
lines to pass `-D' options to the compiler can get quite long.
This causes two problems. One is that the make output is hard to
visually scan for errors. More seriously, the command lines can exceed
the length limits of some operating systems. As an alternative to
passing `-D' options to the compiler, configure scripts can
create a C header file containing `#define' directives. The
AC_CONFIG_HEADER macro selects this kind of output. It should be
called right after AC_INIT.
The package should `#include' the configuration header file before
any other header files, to prevent inconsistencies in declarations (for
example, if it redefines const). Use `#include <config.h>'
instead of `#include "config.h"', and pass the C compiler a
`-I.' option (or `-I..'; whichever directory contains
`config.h'). That way, even if the source directory is configured
itself (perhaps to make a distribution), other build directories can
also be configured without finding the `config.h' from the source
directory.
AC_OUTPUT create the file(s) in the whitespace-separated
list header-to-create containing C preprocessor #define
statements, and replace `@DEFS@' in generated files with
`-DHAVE_CONFIG_H' instead of the value of DEFS. The usual
name for header-to-create is `config.h'.
If header-to-create already exists and its contents are identical
to what AC_OUTPUT would put in it, it is left alone. Doing this
allows some changes in configuration without needlessly causing object
files that depend on the header file to be recompiled.
Usually the input file is named `header-to-create.in'; however, you can override the input file name by appending to header-to-create, a colon-separated list of input files. Examples:
AC_CONFIG_HEADER(defines.h:defines.hin) AC_CONFIG_HEADER(defines.h:defs.pre:defines.h.in:defs.post)
Doing this allows you to keep your file names acceptable to MS-DOS, or to prepend and/or append boilerplate to the file.
Your distribution should contain a template file that looks as you want
the final header file to look, including comments, with default values
in the #define statements. For example, suppose your
`configure.in' makes these calls:
AC_CONFIG_HEADER(conf.h) AC_CHECK_HEADERS(unistd.h)
Then you could have code like the following in `conf.h.in'.
On systems that have `unistd.h', configure will change the 0
to a 1. On other systems, it will leave the line unchanged.
/* Define as 1 if you have unistd.h. */ #define HAVE_UNISTD_H 0
Alternately, if your code tests for configuration options using
#ifdef instead of #if, a default value can be to
#undef the variable instead of to define it to a value. On
systems that have `unistd.h', configure will change the
second line to read `#define HAVE_UNISTD_H 1'. On other systems,
it will comment that line out (in case the system predefines that
symbol).
/* Define if you have unistd.h. */ #undef HAVE_UNISTD_H
autoheader to Create `config.h.in'
The autoheader program can create a template file of C
`#define' statements for configure to use. If
`configure.in' invokes AC_CONFIG_HEADER(file),
autoheader creates `file.in'; if multiple file
arguments are given, the first one is used. Otherwise,
autoheader creates `config.h.in'.
If you give autoheader an argument, it uses that file instead of
`configure.in' and writes the header file to the standard output
instead of to `config.h.in'. If you give autoheader an
argument of `-', it reads the standard input instead of
`configure.in' and writes the header file to the standard output.
autoheader scans `configure.in' and figures out which C
preprocessor symbols it might define. It copies comments and
#define and #undef statements from a file called
`acconfig.h', which comes with and is installed with Autoconf. It
also uses a file called `acconfig.h' in the current directory, if
present. If you AC_DEFINE any additional symbols, you must
create that file with entries for them. For symbols defined by
AC_CHECK_HEADERS, AC_CHECK_FUNCS, AC_CHECK_SIZEOF,
or AC_CHECK_LIB, autoheader generates comments and
#undef statements itself rather than copying>
The file that autoheader creates contains mainly #define
and #undef statements and their accompanying comments. If
`./acconfig.h' contains the string `@TOP@',
autoheader copies the lines before the line containing
`@TOP@' into the top of the file that it generates. Similarly,
if `./acconfig.h' contains the string `@BOTTOM@',
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.top' (typically `config.h.top') and/or
`file.bot' in the current directory. If they exist,
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
`--localdir=dir' option to use an `acconfig.h' in another
directory, they give you a way to put custom boilerplate in each
individual `config.h.in'.
autoheader accepts the following options:
--help
-h
--localdir=dir
-l dir
--macrodir=dir
-m dir
AC_MACRODIR environment variable
to a directory; this option overrides the environment variable.
--version
In most situations, calling AC_OUTPUT is sufficient to produce
`Makefile's in subdirectories. However, configure scripts
that control more than one independent package can use
AC_CONFIG_SUBDIRS to run configure scripts for other
packages in subdirectories.
AC_OUTPUT run configure in each subdirectory
dir in the given whitespace-separated list. If a given dir
is not found, no error is reported, so a configure script can
configure whichever parts of a large source tree are present. If a
given dir contains `configure.in' but no configure,
the Cygnus configure script found by AC_CONFIG_AUXDIR is
used.
The subdirectory configure scripts are given the same
command line options that were given to this 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 subdirs to the list of directories `dir
...'. `Makefile' rules can use this variable to determine
which subdirectories to recurse into. This macro may be called multiple
times.
By default, configure sets the prefix for files it installs to
`/usr/local'. The user of configure can select a different
prefix using the `--prefix' and `--exec-prefix' options.
There are two ways to change the default: when creating
configure, and when running it.
Some software packages might want to install in a directory besides
`/usr/local' by default. To accomplish that, use the
AC_PREFIX_DEFAULT macro.
It may be convenient for users to have 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
AC_PREFIX_PROGRAM.
PATH, the way the shell does. If program
is found, set the prefix to the parent of the directory containing
program; otherwise leave the prefix specified in
`Makefile.in' unchanged. For example, if program is
gcc and the PATH contains `/usr/local/gnu/bin/gcc',
set the prefix to `/usr/local/gnu'.
configure
The following macros manage version numbers for configure
scripts. Using them is optional.
configure is earlier
than version, print an error message on the standard error output
and do not create configure. For example:
AC_PREREQ(1.8)
This macro is useful if your `configure.in' relies on non-obvious
behavior that changed between Autoconf releases. If it merely needs
recently added macros, then AC_PREREQ is less useful, because the
autoconf program already tells the user which macros are not
found. The same thing happens if `configure.in' is processed by a
version of Autoconf older than when AC_PREREQ was added.
configure
script, with any dollar signs or double-quotes removed. This macro lets
you put a revision stamp from `configure.in' into configure
without RCS or CVS changing it when you check in configure. That
way, you can determine easily which revision of `configure.in' a
particular configure corresponds to.
It is a good idea to call this macro before AC_INIT so that the
revision number is near the top of both `configure.in' and
configure. To support doing that, the AC_REVISION output
begins with `#! /bin/sh', like the normal start of a
configure script does.
For example, this line in `configure.in':
AC_REVISION($Revision: 1.1.1.1 $)dnl
produces this in configure:
#! /bin/sh # From configure.in Revision: 1.30
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 (see section 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
configure runs (see section Caching Results).
Some of these macros set output variables. See section Substitutions in Makefiles, for how to get their values. The phrase "define name" is used below as a shorthand to mean "define C preprocessor symbol name to the value 1". See section Defining C Preprocessor Symbols, for how to get those symbol definitions into your program.
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.
These macros check for particular programs--whether they exist, and in some cases whether they support certain features.
YYTEXT_POINTER if yytext is a `char *' instead
of a `char []'. Also set output variable LEX_OUTPUT_ROOT to
the base of the file name that the lexer generates; usually
`lex.yy', but sometimes something else. These results vary
according to whether lex or flex is being used.
mawk, gawk, nawk, and awk, in that
order, and set output variable AWK to the first one that it
finds. It tries mawk first because that is reported to be the
fastest implementation.
CC is not already set in the
environment, check for gcc, and use cc if that's not found.
Set output variable CC to the name of the compiler found.
If using the GNU C compiler, set shell variable GCC to
`yes', empty otherwise. If output variable CFLAGS was
not already set, set it to `-g -O2' for the GNU C compiler
(`-O2' on systems where GCC does not accept `-g'), or `-g'
for other compilers.
If the C compiler being used does not produce executables that can run
on the system where configure is being run, set the shell
variable cross_compiling to `yes', otherwise `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). See section Manual Configuration, for more on support for cross compiling.
NO_MINUS_C_MINUS_O.
CPP to a command that runs the
C preprocessor. If `$CC -E' doesn't work, it uses `/lib/cpp'.
It is only portable to run CPP on files with a `.c'
extension.
If the current language is C (see section Language Choice), many of the
specific test macros use the value of CPP indirectly by calling
AC_TRY_CPP, AC_CHECK_HEADER, AC_EGREP_HEADER, or
AC_EGREP_CPP.
CXX or CCC (in that order) is set; if so, set output
variable CXX to its value. Otherwise search for a C++ compiler
under likely names (c++, g++, gcc, CC,
cxx, and cc++). If none of those checks succeed, as a
last resort set CXX to gcc.
If using the GNU C++ compiler, set shell variable GXX to
`yes', empty otherwise. If output variable CXXFLAGS was
not already set, set it to `-g -O2' for the GNU C++ compiler
(`-O2' on systems where G++ does not accept `-g'), or `-g'
for other compilers.
If the C++ compiler being used does not produce executables that can run
on the system where configure is being run, set the shell
variable cross_compiling to `yes', otherwise `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). See section Manual Configuration, for more on support for cross compiling.
CXXCPP to a command that runs the
C++ preprocessor. If `$CXX -E' doesn't work, it uses `/lib/cpp'.
It is only portable to run CXXCPP on files with a `.c',
`.C', or `.cc' extension.
If the current language is C++ (see section Language Choice), many of the
specific test macros use the value of CXXCPP indirectly by
calling AC_TRY_CPP, AC_CHECK_HEADER,
AC_EGREP_HEADER, or AC_EGREP_CPP.
F77 is not already
set in the environment, check for g77, f77 and f2c,
in that order. Set the output variable F77 to the name of the
compiler found.
If using g77 (the GNU Fortran 77 compiler), then
AC_PROG_F77 will set the shell variable G77 to `yes',
and empty otherwise. If the output variable FFLAGS was not
already set in the environment, then set it to `-g -02' for
g77 (or `-O2' where g77 does not accept `-g').
Otherwise, set FFLAGS to `-g' for all other Fortran 77
compilers.
F77_NO_MINUS_C_MINUS_O if it
does not.
CC if using the
GNU C compiler and ioctl does not work properly without
`-traditional'. That usually happens when the fixed header files
have not been installed on an old system. Since recent versions of the
GNU C compiler fix the header files automatically when installed, this
is becoming a less prevalent problem.
INSTALL to the path of a BSD compatible
install program, if one is found in the current PATH.
Otherwise, set INSTALL to `dir/install-sh -c',
checking the directories specified to AC_CONFIG_AUX_DIR (or its
default directories) to determine dir (see section Creating Output Files). Also set
the variables INSTALL_PROGRAM and INSTALL_SCRIPT to
`${INSTALL}' and INSTALL_DATA to `${INSTALL} -m 644'.
This macro screens out various instances of install known to not
work. It prefers to find a C program rather than a shell script, for
speed. Instead of `install-sh', it can also use `install.sh',
but that name is obsolete because some make programs have a rule
that creates `install' from it if there is no `Makefile'.
A copy of `install-sh' which you may use comes with Autoconf. If
you use AC_PROG_INSTALL, you must include either
`install-sh' or `install.sh' in your distribution, or
configure will produce an error message saying it can't find
them--even if the system you're on has a good install program.
This check is a safety measure to prevent you from accidentally leaving
that file out, which would prevent your package from installing on
systems that don't have a BSD-compatible install program.
If you need to use your own installation program because it has
features not found in standard install programs, there is no
reason to use AC_PROG_INSTALL; just put the pathname of your
program into your `Makefile.in' files.
flex is found, set output variable LEX to
`flex' and LEXLIB to `-lfl', if that library is in a
standard place. Otherwise set LEX to `lex' and
LEXLIB to `-ll'.
LN_S to `ln -s', otherwise set it to `ln'.
If the link is put in a directory other than the current directory, its
meaning depends on whether `ln' or `ln -s' is used. To safely
create links using `$(LN_S)', either find out which form is used
and adjust the arguments, or always invoke ln in the directory
where the link is to be created.
In other words, it does not work to do
$(LN_S) foo /x/bar
Instead, do
(cd /x && $(LN_S) foo bar)
RANLIB to `ranlib' if ranlib
is found, otherwise to `:' (do nothing).
bison is found, set output variable YACC to
`bison -y'. Otherwise, if byacc is found, set YACC
to `byacc'. Otherwise set YACC to `yacc'.
These macros are used to find programs not covered by the particular
test macros. If you need to check the behavior of a program as well as
find out whether it is present, you have to write your own test for it
(see section Writing Tests). By default, these macros use the environment
variable PATH. If you need to check for a program that might not
be in the user's PATH, you can pass a modified path to use
instead, like this:
AC_PATH_PROG(INETD, inetd, /usr/libexec/inetd, $PATH:/usr/libexec:/usr/sbin:/usr/etc:etc)
AC_CHECK_FILE once for each file listed in files.
Additionally, defines `HAVEfile' for each file found, set to 1.
PATH. If
it is found, set variable to value-if-found, otherwise to
value-if-not-found, if given. Always pass over reject (an
absolute file name) even if it is the first found in the search path; in
that case, set variable using the absolute file name of the
prog-to-check-for found that is not reject. If
variable was already set, do nothing. Calls AC_SUBST for
variable.
PATH. If it is found, set
variable to the name of that program. Otherwise, continue
checking the next program in the list. If none of the programs in the
list are found, set variable to value-if-not-found; if
value-if-not-found is not specified, the value of variable
is not changed. Calls AC_SUBST for variable.
AC_CHECK_PROG, but first looks for prog-to-check-for
with a prefix of the host type as determined by AC_CANONICAL_HOST,
followed by a dash (see section Getting the Canonical System Type). For example, if the user
runs `configure --host=i386-gnu', then this call:
AC_CHECK_TOOL(RANLIB, ranlib, :)
sets RANLIB to `i386-gnu-ranlib' if that program exists in
PATH, or to `ranlib' if that program exists in PATH,
or to `:' if neither program exists.
AC_CHECK_PROG, but set variable to the entire
path of prog-to-check-for if found.
AC_CHECK_PROGS, but if any of progs-to-check-for
are found, set variable to the entire path of the program
found.
The following macros check for the presence of certain C, C++ or Fortran 77 library archive files.
action-if-found is a list of shell commands to run if the link
with the library succeeds; action-if-not-found is a list of
shell commands to run if the link fails. If action-if-found is
not specified, the default action will add `-llibrary' to
LIBS and define `HAVE_LIBlibrary' (in all capitals).
If linking with library results in unresolved symbols, which would be resolved by linking with additional libraries, give those libraries as the other-libraries argument, separated by spaces: `-lXt -lX11'. Otherwise this macro will fail to detect that library is present, because linking the test program will always fail with unresolved symbols.
AC_CHECK_LIB with a
function argument of main. In addition, library can
be written as any of `foo', `-lfoo', or `libfoo.a'. In
all of those cases, the compiler is passed `-lfoo'. However,
library can not be a shell variable; it must be a literal name.
This macro is considered obsolete.
AC_TRY_LINK_FUNC first
with no libraries, then for each library listed in search-libs.
If the function is found, run action-if-found, otherwise run action-if-not-found.
If linking with library results in unresolved symbols, which would be resolved by linking with additional libraries, give those libraries as the other-libraries argument, separated by spaces: `-lXt -lX11'. Otherwise this macro will fail to detect that function is present, because linking the test program will always fail with unresolved symbols.
AC_TRY_LINK_FUNC once for each
library listed in search-libs. Add `-llibrary' to
LIBS for the first library found to contain function, and
execute action-if-found. Otherwise execute
action-if-not-found.
The following macros check for particular C library functions. If there is no macro specifically defined to check for a function you need, and you don't need to check for any special properties of it, then you can use one of the general function check macros.
These macros check for particular C functions--whether they exist, and in some cases how they respond when given certain arguments.
alloca. Tries to get a builtin version by
checking for `alloca.h' or the predefined C preprocessor macros
__GNUC__ and _AIX. If this macro finds `alloca.h',
it defines HAVE_ALLOCA_H.
If those attempts fail, it looks for the function in the standard C
library. If any of those methods succeed, it defines
HAVE_ALLOCA. Otherwise, it sets the output variable
ALLOCA to `alloca.o' and defines C_ALLOCA (so
programs can periodically call `alloca(0)' to garbage collect).
This variable is separate from LIBOBJS so multiple programs can
share the value of ALLOCA without needing to create an actual
library, in case only some of them use the code in LIBOBJS.
This macro does not try to get alloca from the System V R3
`libPW' or the System V R4 `libucb' because those libraries
contain some incompatible functions that cause trouble. Some versions
do not even contain alloca or contain a buggy version. If you
still want to use their alloca, use ar to extract
`alloca.o' from them instead of compiling `alloca.c'.
Source files that use alloca should start with a piece of code
like the following, to declare it properly. In some versions
of AIX, the declaration of alloca must precede everything else
except for comments and preprocessor directives. The #pragma
directive is indented so that pre-ANSI C compilers will ignore it,
rather than choke on it.
/* AIX requires this to be the first thing in the file. */ #ifndef __GNUC__ # if HAVE_ALLOCA_H # include <alloca.h> # else # ifdef _AIX #pragma alloca # else # ifndef alloca /* predefined by HP cc +Olibcalls */ char *alloca (); # endif # endif # endif #endif
closedir function does not return a meaningful value,
define CLOSEDIR_VOID. Otherwise, callers ought to check its
return value for an error indicator.
fnmatch function is available and works (unlike the one on
SunOS 5.4), define HAVE_FNMATCH.
getloadavg function, this macro defines HAVE_GETLOADAVG,
and adds to LIBS any libraries needed to get that function.
Otherwise, it adds `getloadavg.o' to the output variable
LIBOBJS, and possibly defines several other C preprocessor
macros and output variables:
SVR4, DGUX, UMAX, or UMAX4_3 if
on those systems.
NLIST_STRUCT.
NLIST_NAME_UNION.
LDAV_PRIVILEGED,
programs need to be installed specially on this system for
getloadavg to work, and this macro defines
GETLOADAVG_PRIVILEGED.
NEED_SETGID. The value is
`true' if special installation is required, `false' if not.
If NEED_SETGID is `true', this macro sets KMEM_GROUP
to the name of the group that should own the installed program.
getmntent in the `sun', `seq', and `gen'
libraries, for Irix 4, PTX, and Unixware, respectively. Then, if
getmntent is available, define HAVE_GETMNTENT.
getpgrp takes no argument (the POSIX.1 version), define
GETPGRP_VOID. Otherwise, it is the BSD version, which takes a
process ID as an argument. This macro does not check whether
getpgrp exists at all; if you need to work in that situation,
first call AC_CHECK_FUNC for getpgrp.
memcmp function is not available, or does not work on
8-bit data (like the one on SunOS 4.1.3), add `memcmp.o' to output
variable LIBOBJS.
mmap function exists and works correctly, define
HAVE_MMAP. Only checks private fixed mapping of already-mapped
memory.
select function's arguments, and defines those types
in SELECT_TYPE_ARG1, SELECT_TYPE_ARG234, and
SELECT_TYPE_ARG5 respectively. SELECT_TYPE_ARG1 defaults
to `int', SELECT_TYPE_ARG234 defaults to `int *',
and SELECT_TYPE_ARG5 defaults to `struct timeval *'.
setpgrp takes no argument (the POSIX.1 version), define
SETPGRP_VOID. Otherwise, it is the BSD version, which takes two
process ID as arguments. This macro does not check whether
setpgrp exists at all; if you need to work in that situation,
first call AC_CHECK_FUNC for setpgrp.
setvbuf takes the buffering type as its second argument and
the buffer pointer as the third, instead of the other way around, define
SETVBUF_REVERSED. This is the case on System V before release 3.
strcoll function exists and works correctly, define
HAVE_STRCOLL. This does a bit more than
`AC_CHECK_FUNCS(strcoll)', because some systems have incorrect
definitions of strcoll, which should not be used.
strftime in the `intl' library, for SCO UNIX.
Then, if strftime is available, define HAVE_STRFTIME.
HAVE_UTIME_NULL.
HAVE_VFORK_H. If a working
vfork is not found, define vfork to be fork. This
macro checks for several known errors in implementations of vfork
and considers the system to not have a working vfork if it
detects any of them. It is not considered to be an implementation error
if a child's invocation of signal modifies the parent's signal
handler, since child processes rarely change their signal handlers.
vprintf is found, define HAVE_VPRINTF. Otherwise, if
_doprnt is found, define HAVE_DOPRNT. (If vprintf
is available, you may assume that vfprintf and vsprintf
are also available.)
wait3 is found and fills in the contents of its third argument
(a `struct rusage *'), which HP-UX does not do, define
HAVE_WAIT3.
These macros are used to find functions not covered by the particular
test macros. If the functions might be in libraries other than the
default C library, first call AC_CHECK_LIB for those libraries.
If you need to check the behavior of a function as well as find out
whether it is present, you have to write your own test for
it (see section Writing Tests).
AC_CHECK_FUNCS instead. This macro checks for functions with C
linkage even when AC_LANG_CPLUSPLUS has been called, since C++ is
more standardized than C is. (see section Language Choice, for more
information about selecting the language for checks.)
HAVE_function (in all capitals). If
action-if-found is given, it is additional shell code to execute
when one of the functions is found. You can give it a value of
`break' to break out of the loop on the first match. If
action-if-not-found is given, it is executed when one of the
functions is not found.
AC_CHECK_FUNCS using an action-if-not-found
that adds `function.o' to the value of the output variable
LIBOBJS. You can declare a function for which your replacement
version is used by enclosing the prototype in `#ifndef
HAVE_function'. If the system has the function, it probably
declares it in a header file you should be including, so you shouldn't
redeclare it, lest your declaration conflict.
The following macros check for the presence of certain C header files. If there is no macro specifically defined to check for a header file you need, and you don't need to check for any special properties of it, then you can use one of the general header file check macros.
These macros check for particular system header files--whether they exist, and in some cases whether they declare certain symbols.
SYS_SIGLIST_DECLARED if the variable sys_siglist is
declared in a system header file, either `signal.h' or
`unistd.h'.
AC_HEADER_DIRENT and AC_FUNC_CLOSEDIR_VOID,
but defines a different set of C preprocessor macros to indicate which
header file is found. This macro and the names it defines are
considered obsolete. The names it defines are:
DIRENT
SYSNDIR
SYSDIR
NDIR
In addition, if the closedir function does not return a
meaningful value, define VOID_CLOSEDIR.
HAVE_DIRENT_H
HAVE_SYS_NDIR_H
HAVE_SYS_DIR_H
HAVE_NDIR_H
The directory library declarations in the source code should look something like the following:
#if HAVE_DIRENT_H # include <dirent.h> # define NAMLEN(dirent) strlen((dirent)->d_name) #else # define dirent direct # define NAMLEN(dirent) (dirent)->d_namlen # if HAVE_SYS_NDIR_H # include <sys/ndir.h> # endif # if HAVE_SYS_DIR_H # include <sys/dir.h> # endif # if HAVE_NDIR_H # include <ndir.h> # endif #endif
Using the above declarations, the program would declare variables to be
type struct dirent, not struct direct, and would access
the length of a directory entry name by passing a pointer to a
struct dirent to the NAMLEN macro.
This macro also checks for the SCO Xenix `dir' and `x' libraries.
major, minor, and
makedev, but `sys/mkdev.h' does, define
MAJOR_IN_MKDEV; otherwise, if `sys/sysmacros.h' does, define
MAJOR_IN_SYSMACROS.
STDC_HEADERS if the system has ANSI C header files.
Specifically, this macro checks for `stdlib.h', `stdarg.h',
`string.h', and `float.h'; if the system has those, it
probably has the rest of the ANSI C header files. This macro also
checks whether `string.h' declares memchr (and thus
presumably the other mem functions), whether `stdlib.h'
declare free (and thus presumably malloc and other related
functions), and whether the `ctype.h' macros work on characters
with the high bit set, as ANSI C requires.
Use STDC_HEADERS instead of __STDC__ to determine whether
the system has ANSI-compliant header files (and probably C library
functions) because many systems that have GCC do not have ANSI C header
files.
On systems without ANSI C headers, there is so much variation that it is probably easier to declare the functions you use than to figure out exactly what the system header files declare. Some systems contain a mix of functions ANSI and BSD; some are mostly ANSI but lack `memmove'; some define the BSD functions as macros in `string.h' or `strings.h'; some have only the BSD functions but `string.h'; some declare the memory functions in `memory.h', some in `string.h'; etc. It is probably sufficient to check for one string function and one memory function; if the library has the ANSI versions of those then it probably has most of the others. If you put the following in `configure.in':
AC_HEADER_STDC AC_CHECK_FUNCS(strchr memcpy)
then, in your code, you can put declarations like this:
#if STDC_HEADERS # include <string.h> #else # ifndef HAVE_STRCHR # define strchr index # define strrchr rindex # endif char *strchr (), *strrchr (); # ifndef HAVE_MEMCPY # define memcpy(d, s, n) bcopy ((s), (d), (n)) # define memmove(d, s, n) bcopy ((s), (d), (n)) # endif #endif
If you use a function like memchr, memset, strtok,
or strspn, which have no BSD equivalent, then macros won't
suffice; you must provide an implementation of each function. An easy
way to incorporate your implementations only when needed (since the ones
in system C libraries may be hand optimized) is to, taking memchr
for example, put it in `memchr.c' and use
`AC_REPLACE_FUNCS(memchr)'.
HAVE_SYS_WAIT_H. Incompatibility can occur if `sys/wait.h'
does not exist, or if it uses the old BSD union wait instead of
int to store a status value. If `sys/wait.h' is not POSIX.1
compatible, then instead of including it, define the POSIX.1 macros with
their usual interpretations. Here is an example:
#include <sys/types.h> #if HAVE_SYS_WAIT_H # include <sys/wait.h> #endif #ifndef WEXITSTATUS # define WEXITSTATUS(stat_val) ((unsigned)(stat_val) >> 8) #endif #ifndef WIFEXITED # define WIFEXITED(stat_val) (((stat_val) & 255) == 0) #endif
NEED_MEMORY_H if memcpy, memcmp, etc. are
not declared in `string.h' and `memory.h' exists. This macro
is obsolete; instead, use AC_CHECK_HEADERS(memory.h). See the
example for AC_HEADER_STDC.
HAVE_UNISTD_H if the system has `unistd.h'. This
macro is obsolete; instead, use `AC_CHECK_HEADERS(unistd.h)'.
The way to check if the system supports POSIX.1 is:
#if HAVE_UNISTD_H # include <sys/types.h> # include <unistd.h> #endif #ifdef _POSIX_VERSION /* Code for POSIX.1 systems. */ #endif
_POSIX_VERSION is defined when `unistd.h' is included on
POSIX.1 systems. If there is no `unistd.h', it is definitely not a
POSIX.1 system. However, some non-POSIX.1 systems do have `unistd.h'.
USG if the system does not have `strings.h',
rindex, bzero, etc. This implies that it has
`string.h', strrchr, memset, etc.
The symbol USG is obsolete. Instead of this macro, see the
example for AC_HEADER_STDC.
These macros are used to find system header files not covered by the particular test macros. If you need to check the contents of a header as well as find out whether it is present, you have to write your own test for it (see section Writing Tests).
AC_CHECK_HEADERS instead.
HAVE_header-file (in all capitals). If action-if-found
is given, it is additional shell code to execute when one of the header
files is found. You can give it a value of `break' to break out of
the loop on the first match. If action-if-not-found is given, it
is executed when one of the header files is not found.
The following macros check for certain structures or structure members.
To check structures not listed here, use AC_EGREP_CPP
(see section Examining Declarations) or AC_TRY_COMPILE
(see section Examining Syntax).
S_ISDIR, S_ISREG et al. defined in
`sys/stat.h' do not work properly (returning false positives),
define STAT_MACROS_BROKEN. This is the case on Tektronix UTekV,
Amdahl UTS and Motorola System V/88.
TIME_WITH_SYS_TIME. On some older systems,
`sys/time.h' includes `time.h', but `time.h' is not
protected against multiple inclusion, so programs should not explicitly
include both files. This macro is useful in programs that use, for
example, struct timeval or struct timezone as well as
struct tm. It is best used in conjunction with
HAVE_SYS_TIME_H, which can be checked for using
AC_CHECK_HEADERS(sys/time.h).
#if TIME_WITH_SYS_TIME # include <sys/time.h> # include <time.h> #else # if HAVE_SYS_TIME_H # include <sys/time.h> # else # include <time.h> # endif #endif
struct stat contains an st_blksize member, define
HAVE_ST_BLKSIZE.
struct stat contains an st_blocks member, define
HAVE_ST_BLOCKS. Otherwise, add `fileblocks.o' to the
output variable LIBOBJS.
struct stat contains an st_rdev member, define
HAVE_ST_RDEV.
struct tm, define
TM_IN_SYS_TIME, which means that including `sys/time.h'
had better define struct tm.
struct tm has a
tm_zone member, define HAVE_TM_ZONE. Otherwise, if the
external array tzname is found, define HAVE_TZNAME.
The following macros check for C typedefs. If there is no macro specifically defined to check for a typedef you need, and you don't need to check for any special properties of it, then you can use a general typedef check macro.
These macros check for particular C typedefs in `sys/types.h' and `stdlib.h' (if it exists).
GETGROUPS_T to be whichever of gid_t or int
is the base type of the array argument to getgroups.
mode_t is not defined, define mode_t to be int.
off_t is not defined, define off_t to be long.
pid_t is not defined, define pid_t to be int.
signal as returning a pointer to a
function returning void, define RETSIGTYPE to be
void; otherwise, define it to be int.
Define signal handlers as returning type RETSIGTYPE:
RETSIGTYPE
hup_handler ()
{
...
}
size_t is not defined, define size_t to be
unsigned.
uid_t is not defined, define uid_t to be int and
gid_t to be int.
This macro is used to check for typedefs not covered by the particular test macros.
The following macros check for C compiler or machine architecture
features. To check for characteristics not listed here, use
AC_TRY_COMPILE (see section Examining Syntax) or AC_TRY_RUN
(see section Checking Run Time Behavior)
WORDS_BIGENDIAN.
const,
define const to be empty. Some C compilers that do not define
__STDC__ do support const; some compilers that define
__STDC__ do not completely support const. Programs can
simply use const as if every C compiler supported it; for those
that don't, the `Makefile' or configuration header file will define
it as empty.
inline, do nothing.
Otherwise define inline to __inline__ or __inline
if it accepts one of those, otherwise define inline to be empty.
char is unsigned, define __CHAR_UNSIGNED__,
unless the C compiler predefines it.
long double type, define
HAVE_LONG_DOUBLE. Some C compilers that do not define
__STDC__ do support the long double type; some compilers
that define __STDC__ do not support long double.
HAVE_STRINGIZE. The stringizing operator is `#' and is
found in macros such as this:
#define x(y) #y
SIZEOF_uctype to be the size in bytes of the C (or
C++) builtin type type, e.g. `int' or `char *'. If
`type' is unknown to the compiler, it gets a size of 0. uctype
is type, with lowercase converted to uppercase, spaces changed to
underscores, and asterisks changed to `P'. If cross-compiling, the
value cross-size is used if given, otherwise configure
exits with an error message.
For example, the call
AC_CHECK_SIZEOF(int *)
defines SIZEOF_INT_P to be 8 on DEC Alpha AXP systems.
int is 16 bits wide, define INT_16_BITS.
This macro is obsolete; it is more general to use
`AC_CHECK_SIZEOF(int)' instead.
long int is 64 bits wide, define
LONG_64_BITS. This macro is obsolete; it is more general to use
`AC_CHECK_SIZEOF(long)' instead.
The following macros check for Fortran 77 compiler characteristics. To
check for characteristics not listed here, use AC_TRY_COMPILE
(see section Examining Syntax) or AC_TRY_RUN (see section Checking Run Time Behavior),
making sure to first set the current lanuage to Fortran 77
AC_LANG_FORTRAN77 (see section Language Choice).
FLIBS is set to these flags.
This macro is intended to be used in those situations when it is necessary to mix, e.g. C++ and Fortran 77 source code into a single program or shared library (see section `Mixing Fortran 77 With C and C++' in GNU Automake).
For example, if object files from a C++ and Fortran 77 compiler must be linked together, then the C++ compiler/linker must be used for linking (since special C++-ish things need to happen at link time like calling global constructors, instantiating templates, enabling exception support, etc.).
However, the Fortran 77 intrinsic and run-time libraries must be linked
in as well, but the C++ compiler/linker doesn't know by default how to
add these Fortran 77 libraries. Hence, the macro
AC_F77_LIBRARY_LDFLAGS was created to determine these Fortran 77
libraries.
The following macros check for operating system services or capabilities.
CYGWIN to `yes'. If not present, sets CYGWIN
to the empty string.
EXEEXT based on the output of the
compiler, after .c, .o, and .obj files have been excluded. Typically
set to empty string if Unix, `.exe' or `.EXE' if Win32.
OBJEXT based on the output of the
compiler, after .c files have been excluded. Typically
set to `.o' if Unix, `.obj' if Win32.
MINGW32 to `yes'. If not present, sets
MINGW32 to the empty string.
xmkmf on a
trivial `Imakefile' and examining the `Makefile' that it
produces. If that fails (such as if xmkmf is not present), look
for them in several directories where they often reside. If either
method is successful, set the shell variables x_includes and
x_libraries to their locations, unless they are in directories
the compiler searches by default.
If both methods fail, or the user gave the command line option
`--without-x', set the shell variable no_x to `yes';
otherwise set it to the empty string.
AC_PATH_X. It adds the C compiler flags that
X needs to output variable X_CFLAGS, and the X linker flags to
X_LIBS. If X is not available, adds `-DX_DISPLAY_MISSING' to
X_CFLAGS.
This macro also checks for special libraries that some systems need in
order to compile X programs. It adds any that the system needs to
output variable X_EXTRA_LIBS. And it checks for special X11R6
libraries that need to be linked with before `-lX11', and adds any
found to the output variable X_PRE_LIBS.
configure.in can check
the shell variable interpval; it will be set to `yes'
if the system supports `#!', `no' if not.
HAVE_LONG_FILE_NAMES.
HAVE_RESTARTABLE_SYSCALLS.
The following macros check for certain operating systems that need special treatment for some programs, due to exceptional oddities in their header files or libraries. These macros are warts; they will be replaced by a more systematic approach, based on the functions they make available or the environments they provide.
_ALL_SOURCE. Allows the use of some BSD
functions. Should be called before any macros that run the C compiler.
LIBS. This macro is obsolete; instead, use
AC_FUNC_GETMNTENT.
LIBS. This macro is obsolete. If you were using it to get
getmntent, use AC_FUNC_GETMNTENT instead. If you used it
for the NIS versions of the password and group functions, use
`AC_CHECK_LIB(sun, getpwnam)'.
_POSIX_SOURCE and add
`-posix' (for the GNU C compiler) or `-Xp' (for other C
compilers) to output variable CC. This allows the use of
POSIX facilities. Must be called after AC_PROG_CC and before
any other macros that run the C compiler.
_MINIX and _POSIX_SOURCE and define
_POSIX_1_SOURCE to be 2. This allows the use of POSIX
facilities. Should be called before any macros that run the C compiler.
LIBS.
This macro is obsolete; instead, use AC_FUNC_STRFTIME.
LIBS. Also, if
`dirent.h' is being used, add `-ldir' to LIBS. This
macro is obsolete; use AC_HEADER_DIRENT instead.
If the existing feature tests don't do something you need, you have to write new ones. These macros are the building blocks. They provide ways for other macros to check whether various kinds of features are available and report the results.
This chapter contains some suggestions and some of the reasons why the existing tests are written the way they are. You can also learn a lot about how to write Autoconf tests by looking at the existing ones. If something goes wrong in one or more of the Autoconf tests, this information can help you understand the assumptions behind them, which might help you figure out how to best solve the problem.
These macros check the output of the C compiler system. They do not cache the results of their tests for future use (see section Caching Results), because they don't know enough about the information they are checking for to generate a cache variable name. They also do not print any messages, for the same reason. The checks for particular kinds of C features call these macros and do cache their results and print messages about what they're checking for.
When you write a feature test that could be applicable to more than one software package, the best thing to do is encapsulate it in a new macro. See section Writing Macros, for how to do that.
The macro AC_TRY_CPP is used to check whether particular header
files exist. You can check for one at a time, or more than one if you
need several header files to all exist for some purpose.
#include statements and declarations,
on which shell variable, backquote, and backslash substitutions are
performed. (Actually, it can be any C program, but other statements are
probably not useful.) If the preprocessor produces no error messages
while processing it, run shell commands action-if-true. Otherwise
run shell commands action-if-false.
This macro uses CPPFLAGS, but not CFLAGS, because
`-g', `-O', etc. are not valid options to many C
preprocessors.
Here is how to find out whether a header file contains a particular
declaration, such as a typedef, a structure, a structure member, or a
function. Use AC_EGREP_HEADER instead of running grep
directly on the header file; on some systems the symbol might be defined
in another header file that the file you are checking `#include's.
egrep regular expression
pattern, execute shell commands action-if-found, otherwise
execute action-if-not-found.
To check for C preprocessor symbols, either defined by header files or
predefined by the C preprocessor, use AC_EGREP_CPP. Here is an
example of the latter:
AC_EGREP_CPP(yes, [#ifdef _AIX yes #endif ], is_aix=yes, is_aix=no)
egrep regular expression pattern, execute shell commands
action-if-found, otherwise execute action-if-not-found.
This macro calls AC_PROG_CPP or AC_PROG_CXXCPP (depending
on which language is current, see section Language Choice), if it hasn't
been called already.
To check for a syntax feature of the C, C++ or Fortran 77 compiler, such
as whether it recognizes a certain keyword, use AC_TRY_COMPILE to
try to compile a small program that uses that feature. You can also use
it to check for structures and structure members that are not present on
all systems.
For C and C++, includes is any #include statements needed
by the code in function-body (includes will be ignored if
the currently selected language is Fortran 77). This macro also uses
CFLAGS or CXXFLAGS if either C or C++ is the currently
selected language, as well as CPPFLAGS, when compiling. If
Fortran 77 is the currently selected language then FFLAGS will be
used when compiling.
If the file compiles successfully, run shell commands action-if-found, otherwise run action-if-not-found.
This macro does not try to link; use AC_TRY_LINK if you need to
do that (see section Examining Libraries).
To check for a library, a function, or a global variable, Autoconf
configure scripts try to compile and link a small program that
uses it. This is unlike Metaconfig, which by default uses nm
or ar on the C library to try to figure out which functions are
available. Trying to link with the function is usually a more reliable
approach because it avoids dealing with the variations in the options
and output formats of nm and ar and in the location of the
standard libraries. It also allows configuring for cross-compilation or
checking a function's runtime behavior if needed. On the other hand, it
can be slower than scanning the libraries once.
A few systems have linkers that do not return a failure exit status when
there are unresolved functions in the link. This bug makes the
configuration scripts produced by Autoconf unusable on those systems.
However, some of them can be given options that make the exit status
correct. This is a problem that Autoconf does not currently handle
automatically. If users encounter this problem, they might be able to
solve it by setting LDFLAGS in the environment to pass whatever
options the linker needs (for example, `-Wl,-dn' on MIPS RISC/OS).
AC_TRY_LINK is used to compile test programs to test for
functions and global variables. It is also used by AC_CHECK_LIB
to check for libraries (see section Library Files), by adding the library being
checked for to LIBS temporarily and trying to link a small
program.
For C and C++, includes is any #include statements needed
by the code in function-body (includes will be ignored if
the currently selected language is Fortran 77). This macro also uses
CFLAGS or CXXFLAGS if either C or C++ is the currently
selected language, as well as CPPFLAGS, when compiling. If
Fortran 77 is the currently selected language then FFLAGS will be
used when compiling. However, both LDFLAGS and LIBS will
be used during linking in all cases.
If the file compiles and links successfully, run shell commands action-if-found, otherwise run action-if-not-found.
If the file compiles and links successfully, run shell commands action-if-found, otherwise run action-if-not-found.
AC_TRY_LINK, with the addition
that it prints `checking for echo-text' to the standard
output first, if echo-text is non-empty. Use
AC_MSG_CHECKING and AC_MSG_RESULT instead to print
messages (see section Printing Messages).
Sometimes you need to find out how a system performs at run time, such as whether a given function has a certain capability or bug. If you can, make such checks when your program runs instead of when it is configured. You can check for things like the machine's endianness when your program initializes itself.
If you really need to test for a run-time behavior while configuring,
you can write a test program to determine the result, and compile and
run it using AC_TRY_RUN. Avoid running test programs if
possible, because using them prevents people from configuring your
package for cross-compiling.
Use the following macro if you need to test run-time behavior of the system while configuring.
CFLAGS or
CXXFLAGS, CPPFLAGS, LDFLAGS, and LIBS when
compiling.
If the C compiler being used does not produce executables that run on
the system where configure is being run, then the test program is
not run. If the optional shell commands action-if-cross-compiling
are given, they are run instead. Otherwise, configure prints
an error message and exits.
Try to provide a pessimistic default value to use when cross-compiling
makes run-time tests impossible. You do this by passing the optional
last argument to AC_TRY_RUN. autoconf prints a warning
message when creating configure each time it encounters a call to
AC_TRY_RUN with no action-if-cross-compiling argument
given. You may ignore the warning, though users will not be able to
configure your package for cross-compiling. A few of the macros
distributed with Autoconf produce this warning message.
To configure for cross-compiling you can also choose a value for those parameters based on the canonical system name (see section Manual Configuration). Alternatively, set up a test results cache file with the correct values for the target system (see section Caching Results).
To provide a default for calls of AC_TRY_RUN that are embedded in
other macros, including a few of the ones that come with Autoconf, you
can call AC_PROG_CC before running them. Then, if the shell
variable cross_compiling is set to `yes', use an alternate
method to get the results instead of calling the macros.
Test programs should not write anything to the standard output. They
should return 0 if the test succeeds, nonzero otherwise, so that success
can be distinguished easily from a core dump or other failure;
segmentation violations and other failures produce a nonzero exit
status. Test programs should exit, not return, from
main, because on some systems (old Suns, at least) the argument
to return in main is ignored.
Test programs can use #if or #ifdef to check the values of
preprocessor macros defined by tests that have already run. For
example, if you call AC_HEADER_STDC, then later on in
`configure.in' you can have a test program that includes an ANSI C
header file conditionally:
#if STDC_HEADERS # include <stdlib.h> #endif
If a test program needs to use or create a data file, give it a name
that starts with `conftest', such as `conftestdata'. The
configure script cleans up by running `rm -rf conftest*'
after running test programs and if the script is interrupted.
Function declarations in test programs should have a prototype conditionalized for C++. In practice, though, test programs rarely need functions that take arguments.
#ifdef __cplusplus foo(int i) #else foo(i) int i; #endif
Functions that test programs declare should also be conditionalized for C++, which requires `extern "C"' prototypes. Make sure to not include any header files containing clashing prototypes.
#ifdef __cplusplus extern "C" void *malloc(size_t); #else char *malloc(); #endif
If a test program calls a function with invalid parameters (just to see
whether it exists), organize the program to ensure that it never invokes
that function. You can do this by calling it in another function that is
never invoked. You can't do it by putting it after a call to
exit, because GCC version 2 knows that exit never returns
and optimizes out any code that follows it in the same block.
If you include any header files, make sure to call the functions
relevant to them with the correct number of arguments, even if they are
just 0, to avoid compilation errors due to prototypes. GCC version 2
has internal prototypes for several functions that it automatically
inlines; for example, memcpy. To avoid errors when checking for
them, either pass them the correct number of arguments or redeclare them
with a different return type (such as char).
When writing your own checks, there are some shell script programming
techniques you should avoid in order to make your code portable. The
Bourne shell and upward-compatible shells like Bash and the Korn shell
have evolved over the years, but to prevent trouble, do not take
advantage of features that were added after UNIX version 7, circa 1977.
You should not use shell functions, aliases, negated character classes,
or other features that are not found in all Bourne-compatible shells;
restrict yourself to the lowest common denominator. Even unset
is not supported by all shells! Also, include a space after the
exclamation point in interpreter specifications, like this:
#! /usr/bin/perl
If you omit the space before the path, then 4.2BSD based systems (such as Sequent DYNIX) will ignore the line, because they interpret `#! /' as a 4-byte magic number.
The set of external programs you should run in a configure script
is fairly small. See section `Utilities in Makefiles' in GNU Coding Standards, for the list. This
restriction allows users to start out with a fairly small set of
programs and build the rest, avoiding too many interdependencies between
packages.
Some of these external utilities have a portable subset of features, as
well; for example, don't rely on ln having a `-f' option or
cat having any options. sed scripts should not contain
comments or use branch labels longer than 8 characters. Don't use
`grep -s' to suppress output, because `grep -s' on System V
does not suppress output, only error messages. Instead, redirect the
standard output and standard error (in case the file doesn't exist) of
grep to `/dev/null'. Check the exit status of grep
to determine whether it found a match.
configure scripts need to test properties of many files and
strings. Here are some portability problems to watch out for when doing
those tests.
The test program is the way to perform many file and string
tests. It is often invoked by the alternate name `[', but using
that name in Autoconf code is asking for trouble since it is an
m4 quote character.
If you need to make multiple checks using test, combine
them with the shell operators `&&' and `||' instead of using
the test operators `-a' and `-o'. On System V, the
precedence of `-a' and `-o' is wrong relative to the unary
operators; consequently, POSIX does not specify them, so using them is
nonportable. If you combine `&&' and `||' in the same
statement, keep in mind that they have equal precedence.
To enable configure scripts to support cross-compilation, they
shouldn't do anything that tests features of the host system instead of
the target system. But occasionally you may find it necessary to check
whether some arbitrary file exists. To do so, use `test -f' or
`test -r'. Do not use `test -x', because 4.3BSD does not have
it.
Another nonportable shell programming construction is
var=${var:-value}
The intent is to set var to value only if it is not already
set, but if var has any value, even the empty string, to leave it
alone. Old BSD shells, including the Ultrix sh, don't accept
the colon, and complain and die. A portable equivalent is
: ${var=value}
Some operations are accomplished in several possible ways, depending on the UNIX variant. Checking for them essentially requires a "case statement". Autoconf does not directly provide one; however, it is easy to simulate by using a shell variable to keep track of whether a way to perform the operation has been found yet.
Here is an example that uses the shell variable fstype to keep
track of whether the remaining cases need to be checked.
AC_MSG_CHECKING(how to get filesystem type) fstype=no # The order of these tests is important. AC_TRY_CPP([#include <sys/statvfs.h> #include <sys/fstyp.h>], AC_DEFINE(FSTYPE_STATVFS) fstype=SVR4) if test $fstype = no; then AC_TRY_CPP([#include <sys/statfs.h> #include <sys/fstyp.h>], AC_DEFINE(FSTYPE_USG_STATFS) fstype=SVR3) fi if test $fstype = no; then AC_TRY_CPP([#include <sys/statfs.h> #include <sys/vmount.h>], AC_DEFINE(FSTYPE_AIX_STATFS) fstype=AIX) fi # (more cases omitted here) AC_MSG_RESULT($fstype)
Packages that use both C and C++ need to test features of both
compilers. Autoconf-generated configure scripts check for C
features by default. The following macros determine which language's
compiler is used in tests that follow in `configure.in'.
CC and CPP and use extension
`.c' for test programs. Set the shell variable
cross_compiling to the value computed by AC_PROG_CC if it
has been run, empty otherwise.
CXX and CXXCPP and use
extension `.C' for test programs. Set the shell variable
cross_compiling to the value computed by AC_PROG_CXX if
it has been run, empty otherwise.
F77 and use extension `.f' for
test programs. Set the shell variable cross_compiling to the
value computed by AC_PROG_F77 if it has been run, empty
otherwise.
AC_LANG_C,
AC_LANG_CPLUSPLUS or AC_LANG_FORTRAN77) on a stack. Does
not change which language is current. Use this macro and
AC_LANG_RESTORE in macros that need to temporarily switch to a
particular language.
AC_LANG_SAVE, and remove it from the stack. This macro is
equivalent to either AC_LANG_C, AC_LANG_CPLUSPLUS or
AC_LANG_FORTRAN77, whichever had been run most recently when
AC_LANG_SAVE was last called.
Do not call this macro more times than AC_LANG_SAVE.
AC_REQUIRE (see section Prerequisite Macros) with an
argument of either AC_PROG_CPP or AC_PROG_CXXCPP,
depending on which language is current.
Once configure has determined whether a feature exists, what can
it do to record that information? There are four sorts of things it can
do: define a C preprocessor symbol, set a variable in the output files,
save the result in a cache file for future configure runs, and
print a message letting the user know the result of the test.
A common action to take in response to a feature test is to define a C
preprocessor symbol indicating the results of the test. That is done by
calling AC_DEFINE or AC_DEFINE_UNQUOTED.
By default, AC_OUTPUT places the symbols defined by these macros
into the output variable DEFS, which contains an option
`-Dsymbol=value' for each symbol defined. Unlike in
Autoconf version 1, there is no variable DEFS defined while
configure is running. To check whether Autoconf macros have
already defined a certain C preprocessor symbol, test the value of the
appropriate cache variable, as in this example:
AC_CHECK_FUNC(vprintf, AC_DEFINE(HAVE_VPRINTF)) if test "$ac_cv_func_vprintf" != yes; then AC_CHECK_FUNC(_doprnt, AC_DEFINE(HAVE_DOPRNT)) fi
If AC_CONFIG_HEADER has been called, then instead of creating
DEFS, AC_OUTPUT creates a header file by substituting the
correct values into #define statements in a template file.
See section Configuration Header Files, for more information about this kind of
output.
AC_CONFIG_HEADER it should not contain any `#'
characters, as make tends to eat them. To use a shell variable
(which you need to do in order to define a value containing the
m4 quote characters `[' or `]'), use
AC_DEFINE_UNQUOTED instead. description is only useful if
you are using AC_CONFIG_HEADER. In this case, description
is put into the generated `config.h.in' as the comment before the
macro define; the macro need not be mentioned in `acconfig.h'. The
following example defines the C preprocessor variable EQUATION to
be the string constant `"$a > $b"':
AC_DEFINE(EQUATION, "$a > $b")
AC_DEFINE, but three shell expansions are
performed--once--on variable and value: variable expansion
(`$'), command substitution (``'), and backslash escaping
(`\'). Single and double quote characters in the value have no
special meaning. Use this macro instead of AC_DEFINE when
variable or value is a shell variable. Examples:
AC_DEFINE_UNQUOTED(config_machfile, "${machfile}")
AC_DEFINE_UNQUOTED(GETGROUPS_T, $ac_cv_type_getgroups)
AC_DEFINE_UNQUOTED(${ac_tr_hdr})
Due to the syntactical bizarreness of the Bourne shell, do not use
semicolons to separate AC_DEFINE or AC_DEFINE_UNQUOTED
calls from other macro calls or shell code; that can cause syntax errors
in the resulting configure script. Use either spaces or
newlines. That is, do this:
AC_CHECK_HEADER(elf.h, AC_DEFINE(SVR4) LIBS="$LIBS -lelf")
or this:
AC_CHECK_HEADER(elf.h, AC_DEFINE(SVR4) LIBS="$LIBS -lelf")
instead of this:
AC_CHECK_HEADER(elf.h, AC_DEFINE(SVR4); LIBS="$LIBS -lelf")
One way to record the results of tests is to set output variables,
which are shell variables whose values are substituted into files that
configure outputs. The two macros below create new output
variables. See section Preset Output Variables, for a list of output
variables that are always available.
AC_OUTPUT
substitute the variable variable into output files (typically one
or more `Makefile's). This means that AC_OUTPUT will
replace instances of `@variable@' in input files with the
value that the shell variable variable has when AC_OUTPUT
is called. The value of variable should not contain literal
newlines.
AC_OUTPUT insert (without substitutions) the contents of the file
named by shell variable variable into output files. This means
that AC_OUTPUT will replace instances of
`@variable@' in output files (such as `Makefile.in')
with the contents of the file that the shell variable variable
names when AC_OUTPUT is called. Set the variable to
`/dev/null' for cases that do not have a file to insert.
This macro is useful for inserting `Makefile' fragments containing
special dependencies or other make directives for particular host
or target types into `Makefile's. For example, `configure.in'
could contain:
AC_SUBST_FILE(host_frag)dnl host_frag=$srcdir/conf/sun4.mh
and then a `Makefile.in' could contain:
@host_frag@
To avoid checking for the same features repeatedly in various
configure scripts (or repeated runs of one script),
configure saves the results of many of its checks in a cache
file. If, when a configure script runs, it finds a cache file,
it reads from it the results from previous runs and avoids rerunning
those checks. As a result, configure can run much faster than if
it had to perform all of the checks every time.
configure was not given the `--quiet' or
`--silent' option, print a message saying that the result was
cached; otherwise, run the shell commands commands-to-set-it.
Those commands should have no side effects except for setting the
variable cache-id. In particular, they should not call
AC_DEFINE; the code that follows the call to AC_CACHE_VAL
should do that, based on the cached value. Also, they should not print
any messages, for example with AC_MSG_CHECKING; do that before
calling AC_CACHE_VAL, so the messages are printed regardless of
whether the results of the check are retrieved from the cache or
determined by running the shell commands. If the shell commands are run
to determine the value, the value will be saved in the cache file just
before configure creates its output files. See section Cache Variable Names, for how to choose the name of the cache-id variable.
AC_CACHE_VAL that takes care of printing the
messages. This macro provides a convenient shorthand for the most
common way to use these macros. It calls AC_MSG_CHECKING for
message, then AC_CACHE_VAL with the cache-id and
commands arguments, and AC_MSG_RESULT with cache-id.
AC_INIT.
AC_OUTPUT, but it can be quite useful to call
AC_CACHE_SAVE at key points in configure.in. Doing so
checkpoints the cache in case of an early configure script abort.
The names of cache variables should have the following format:
package-prefix_cv_value-type_specific-value[_additional-options]
for example, `ac_cv_header_stat_broken' or `ac_cv_prog_gcc_traditional'. The parts of the variable name are:
_cv_
The values assigned to cache variables may not contain newlines. Usually, their values will be boolean (`yes' or `no') or the names of files or functions; so this is not an important restriction.
A cache file is a shell script that caches the results of configure tests run on one system so they can be shared between configure scripts and configure runs. It is not useful on other systems. If its contents are invalid for some reason, the user may delete or edit it.
By default, configure uses `./config.cache' as the cache file,
creating it if it does not exist already. configure accepts the
`--cache-file=file' option to use a different cache file;
that is what configure does when it calls configure
scripts in subdirectories, so they share the cache.
See section Configuring Other Packages in Subdirectories, for information on configuring subdirectories
with the AC_CONFIG_SUBDIRS macro.
Giving `--cache-file=/dev/null' disables caching, for debugging
configure. `config.status' only pays attention to the cache
file if it is given the `--recheck' option, which makes it rerun
configure. If you are anticipating a long debugging period, you
can also disable cache loading and saving for a configure script
by redefining the cache macros at the start of `configure.in':
define([AC_CACHE_LOAD], )dnl define([AC_CACHE_SAVE], )dnl AC_INIT(whatever) ... rest of configure.in ...
It is wrong to try to distribute cache files for particular system types. There is too much room for error in doing that, and too much administrative overhead in maintaining them. For any features that can't be guessed automatically, use the standard method of the canonical system type and linking files (see section Manual Configuration).
The cache file on a particular system will gradually accumulate whenever
someone runs a configure script; it will be initially
nonexistent. Running configure merges the new cache results with
the existing cache file. The site initialization script can specify a
site-wide cache file to use instead of the default, to make it work
transparently, as long as the same C compiler is used every time
(see section Setting Site Defaults).
If your configure script, or a macro called from configure.in, happens to abort the configure process, it may be useful to checkpoint the cache a few times at key points. Doing so will reduce the amount of time it takes to re-run the configure script with (hopefully) the error that caused the previous abort corrected.
... AC_INIT, etc. ... dnl checks for programs AC_PROG_CC AC_PROG_GCC_TRADITIONAL ... more program checks ... AC_CACHE_SAVE dnl checks for libraries AC_CHECK_LIB(nsl, gethostbyname) AC_CHECK_LIB(socket, connect) ... more lib checks ... AC_CACHE_SAVE dnl Might abort... AM_PATH_GTK(1.0.2, , exit 1) AM_PATH_GTKMM(0.9.5, , exit 1)
configure scripts need to give users running them several kinds
of information. The following macros print messages in ways appropriate
for each kind. The arguments to all of them get enclosed in shell
double quotes, so the shell performs variable and backquote substitution
on them. You can print a message containing a comma by quoting the
message with the m4 quote characters:
AC_MSG_RESULT([never mind, I found the BASIC compiler])
These macros are all wrappers around the echo shell command.
configure scripts should rarely need to run echo directly
to print messages for the user. Using these macros makes it easy to
change how and when each kind of message is printed; such changes need
only be made to the macro definitions, and all of the callers change
automatically.
configure is checking for a particular
feature. This macro prints a message that starts with `checking '
and ends with `...' and no newline. It must be followed by a call
to AC_MSG_RESULT to print the result of the check and the
newline. The feature-description should be something like
`whether the Fortran compiler accepts C++ comments' or `for
c89'.
This macro prints nothing if configure is run with the
`--quiet' or `--silent' option.
AC_MSG_CHECKING, and the result-description should be
the completion of the message printed by the call to
AC_MSG_CHECKING.
This macro prints nothing if configure is run with the
`--quiet' or `--silent' option.
configure from
completing. This macro prints an error message on the standard error
output and exits configure with a nonzero status.
error-description should be something like `invalid value
$HOME for \$HOME'.
configure user of a possible problem. This macro
prints the message on the standard error output; configure
continues running afterward, so macros that call AC_MSG_WARN should
provide a default (back-up) behavior for the situations they warn about.
problem-description should be something like `ln -s seems to
make hard links'.
The following two macros are an obsolete alternative to
AC_MSG_CHECKING and AC_MSG_RESULT.
AC_MSG_CHECKING, except that it prints a
newline after the feature-description. It is useful mainly to
print a general description of the overall purpose of a group of feature
checks, e.g.,
AC_CHECKING(if stack overflow is detectable)
AC_MSG_RESULT, except that it is meant
to follow a call to AC_CHECKING instead of
AC_MSG_CHECKING; it starts the message it prints with a tab. It
is considered obsolete.
When you write a feature test that could be applicable to more than one software package, the best thing to do is encapsulate it in a new macro. Here are some instructions and guidelines for writing Autoconf macros.
Autoconf macros are defined using the AC_DEFUN macro, which is
similar to the m4 builtin define macro. In addition to
defining a macro, AC_DEFUN adds to it some code which is used to
constrain the order in which macros are called (see section Prerequisite Macros).
An Autoconf macro definition looks like this:
AC_DEFUN(macro-name, [macro-body])
The square brackets here do not indicate optional text: they should literally be present in the macro definition to avoid macro expansion problems (see section Quoting). You can refer to any arguments passed to the macro as `$1', `$2', etc.
To introduce comments in m4, use the m4 builtin
dnl; it causes m4 to discard the text through the next
newline. It is not needed between macro definitions in `acsite.m4'
and `aclocal.m4', because all output is discarded until
AC_INIT is called.
See section `How to define new macros' in GNU m4, for
more complete information on writing m4 macros.
All of the Autoconf macros have all-uppercase names starting with `AC_' to prevent them from accidentally conflicting with other text. All shell variables that they use for internal purposes have mostly-lowercase names starting with `ac_'. To ensure that your macros don't conflict with present or future Autoconf macros, you should prefix your own macro names and any shell variables they use with some other sequence. Possibilities include your initials, or an abbreviation for the name of your organization or software package.
Most of the Autoconf macros' names follow a structured naming convention that indicates the kind of feature check by the name. The macro names consist of several words, separated by underscores, going from most general to most specific. The names of their cache variables use the same convention (see section Cache Variable Names, for more information on them).
The first word of the name after `AC_' usually tells the category of feature being tested. Here are the categories used in Autoconf for specific test macros, the kind of macro that you are more likely to write. They are also used for cache variables, in all-lowercase. Use them where applicable; where they're not, invent your own categories.
C
DECL
FUNC
GROUP
HEADER
LIB
PATH
PROG
STRUCT
SYS
TYPE
VAR
After the category comes the name of the particular feature being
tested. Any further words in the macro name indicate particular aspects
of the feature. For example, AC_FUNC_UTIME_NULL checks the
behavior of the utime function when called with a NULL
pointer.
A macro that is an internal subroutine of another macro should have a
name that starts with the name of that other macro, followed by one or
more words saying what the internal macro does. For example,
AC_PATH_X has internal macros AC_PATH_X_XMKMF and
AC_PATH_X_DIRECT.
Macros that are called by other macros are evaluated by m4
several times; each evaluation might require another layer of quotes to
prevent unwanted expansions of macros or m4 builtins, such as
`define' and `$1'. Quotes are also required around macro
arguments that contain commas, since commas separate the arguments from
each other. It's a good idea to quote any macro arguments that contain
newlines or calls to other macros, as well.
Autoconf changes the m4 quote characters
from the default ``' and `'' to `[' and `]', because
many of the macros use ``' and `'', mismatched. However, in a
few places the macros need to use brackets (usually in C program text or
regular expressions). In those places, they use the m4 builtin
command changequote to temporarily change the quote characters to
`<<' and `>>'. (Sometimes, if they don't need to quote
anything, they disable quoting entirely instead by setting the quote
characters to empty strings.) Here is an example:
AC_TRY_LINK( changequote(<<, >>)dnl <<#include <time.h> #ifndef tzname /* For SGI. */ extern char *tzname[]; /* RS6000 and others reject char **tzname. */ #endif>>, changequote([, ])dnl [atoi(*tzname);], ac_cv_var_tzname=yes, ac_cv_var_tzname=no)
When you create a configure script using newly written macros,
examine it carefully to check whether you need to add more quotes in
your macros. If one or more words have disappeared in the m4
output, you need more quotes. When in doubt, quote.
However, it's also possible to put on too many layers of quotes. If
this happens, the resulting configure script will contain
unexpanded macros. The autoconf program checks for this problem
by doing `grep AC_ configure'.
Some Autoconf macros depend on other macros having been called first in order to work correctly. Autoconf provides a way to ensure that certain macros are called if needed and a way to warn the user if macros are called in an order that might cause incorrect operation.
A macro that you write might need to use values that have previously
been computed by other macros. For example, AC_DECL_YYTEXT
examines the output of flex or lex, so it depends on
AC_PROG_LEX having been called first to set the shell variable
LEX.
Rather than forcing the user of the macros to keep track of the
dependencies between them, you can use the AC_REQUIRE macro to do
it automatically. AC_REQUIRE can ensure that a macro is only
called if it is needed, and only called once.
m4 macro macro-name has not already been called,
call it (without any arguments). Make sure to quote macro-name
with square brackets. macro-name must have been defined using
AC_DEFUN or else contain a call to AC_PROVIDE to indicate
that it has been called.
An alternative to using AC_DEFUN is to use define and call
AC_PROVIDE. Because this technique does not prevent nested
messages, it is considered obsolete.
AC_PROVIDE. An easy way to get it is from the m4 builtin
variable $0, like this:
AC_PROVIDE([$0])
Some macros should be run before another macro if both are called, but neither requires that the other be called. For example, a macro that changes the behavior of the C compiler should be called before any macros that run the C compiler. Many of these dependencies are noted in the documentation.
Autoconf provides the AC_BEFORE macro to warn users when macros
with this kind of dependency appear out of order in a
`configure.in' file. The warning occurs when creating
configure from `configure.in', not when running
configure.
For example, AC_PROG_CPP checks whether the C compiler
can run the C preprocessor when given the `-E' option. It should
therefore be called after any macros that change which C compiler is
being used, such as AC_PROG_CC. So AC_PROG_CC contains:
AC_BEFORE([$0], [AC_PROG_CPP])dnl
This warns the user if a call to AC_PROG_CPP has already occurred
when AC_PROG_CC is called.
m4 print a warning message on the standard error output if
called-macro-name has already been called. this-macro-name
should be the name of the macro that is calling AC_BEFORE. The
macro called-macro-name must have been defined using
AC_DEFUN or else contain a call to AC_PROVIDE to indicate
that it has been called.
Configuration and portability technology has evolved over the years.
Often better ways of solving a particular problem are developed, or
ad-hoc approaches are systematized. This process has occurred in many
parts of Autoconf. One result is that some of the macros are now
considered obsolete; they still work, but are no longer considered
the best thing to do. Autoconf provides the AC_OBSOLETE macro to
warn users producing configure scripts when they use obsolete
macros, to encourage them to modernize. A sample call is:
AC_OBSOLETE([$0], [; use AC_CHECK_HEADERS(unistd.h) instead])dnl
m4 print a message on the standard error output warning that
this-macro-name is obsolete, and giving the file and line number
where it was called. this-macro-name should be the name of the
macro that is calling AC_OBSOLETE. If suggestion is given,
it is printed at the end of the warning message; for example, it can be
a suggestion for what to use instead of this-macro-name.
A few kinds of features can't be guessed automatically by running test
programs. For example, the details of the object file format, or
special options that need to be passed to the compiler or linker. You
can check for such features using ad-hoc means, such as having
configure check the output of the uname program, or
looking for libraries that are unique to particular systems. However,
Autoconf provides a uniform method for handling unguessable features.
Like other GNU configure scripts, Autoconf-generated
configure scripts can make decisions based on a canonical name
for the system type, which has the form:
cpu-company-system
configure can usually guess the canonical name for the type of
system it's running on. To do so it runs a script called
config.guess, which derives the name using the uname
command or symbols predefined by the C preprocessor.
Alternately, the user can specify the system type with command line
arguments to configure. Doing so is necessary when
cross-compiling. In the most complex case of cross-compiling, three
system types are involved. The options to specify them are:
--build=build-type
--host=host-type
--target=target-type
If the user gives configure a non-option argument, it is used as
the default for the host, target, and build system types if the user
does not specify them explicitly with options. The target and build
types default to the host type if it is given and they are not. If you
are cross-compiling, you still have to specify the names of the
cross-tools you use, in particular the C compiler, on the
configure command line, e.g.,
CC=m68k-coff-gcc configure --target=m68k-coff
configure recognizes short aliases for many system types; for
example, `decstation' can be given on the command line instead of
`mips-dec-ultrix4.2'. configure runs a script called
config.sub to canonicalize system type aliases.
The following macros make the system type available to configure
scripts. They run the shell script config.guess to determine any
values for the host, target, and build types that they need and the user
did not specify on the command line. They run config.sub to
canonicalize any aliases the user gave. If you use these macros, you
must distribute those two shell scripts along with your source code.
See section Creating Output Files, for information about the AC_CONFIG_AUX_DIR macro
which you can use to control which directory configure looks for
those scripts in. If you do not use either of these macros,
configure ignores any `--host', `--target', and
`--build' options given to it.
AC_CANONICAL_SYSTEM relevant to the
host type. This is all that is needed for programs that are not part of
a compiler toolchain.
After calling AC_CANONICAL_SYSTEM, the following output variables
contain the system type information. After AC_CANONICAL_HOST,
only the host variables below are set.
build, host, targetbuild_alias, host_alias, target_aliasconfig.guess was used;
build_cpu, build_vendor, build_oshost_cpu, host_vendor, host_ostarget_cpu, target_vendor, target_os
How do you use a canonical system type? Usually, you use it in one or
more case statements in `configure.in' to select
system-specific C files. Then link those files, which have names based
on the system name, to generic names, such as `host.h' or
`target.c'. The case statement patterns can use shell
wildcards to group several cases together, like in this fragment:
case "$target" in i386-*-mach* | i386-*-gnu*) obj_format=aout emulation=mach bfd_gas=yes ;; i960-*-bout) obj_format=bout ;; esac
AC_OUTPUT link each of the existing files source to
the corresponding link name dest. Makes a symbolic link if
possible, otherwise a hard link. The dest and source names
should be relative to the top level source or build directory.
This macro may be called multiple times.
For example, this call:
AC_LINK_FILES(config/${machine}.h config/${obj_format}.h, host.h object.h)
creates in the current directory `host.h', which is a link to `srcdir/config/${machine}.h', and `object.h', which is a link to `srcdir/config/${obj_format}.h'.
You can also use the host system type to find cross-compilation tools.
See section Generic Program and File Checks, for information about the AC_CHECK_TOOL
macro which does that.
configure scripts support several kinds of local configuration
decisions. There are ways for users to specify where external software
packages are, include or exclude optional features, install programs
under modified names, and set default values for configure
options.
Some packages require, or can optionally use, other software packages
which are already installed. The user can give configure
command line options to specify which such external software to use.
The options have one of these forms:
--with-package[=arg] --without-package
For example, `--with-gnu-ld' means work with the GNU linker instead of some other linker. `--with-x' means work with The X Window System.
The user can give an argument by following the package name with `=' and the argument. Giving an argument of `no' is for packages that are used by default; it says to not use the package. An argument that is neither `yes' nor `no' could include a name or number of a version of the other package, to specify more precisely which other package this program is supposed to work with. If no argument is given, it defaults to `yes'. `--without-package' is equivalent to `--with-package=no'.
configure scripts do not complain about
`--with-package' options that they do not support.
This behavior permits configuring a source tree containing multiple
packages with a top-level configure script when the packages
support different options, without spurious error messages about options
that some of the packages support.
An unfortunate side effect is that option spelling errors are not diagnosed.
No better approach to this problem has been suggested so far.
For each external software package that may be used, `configure.in'
should call AC_ARG_WITH to detect whether the configure
user asked to use it. Whether each package is used or not by
default, and which arguments are valid, is up to you.
configure the option `--with-package'
or `--without-package', run shell commands
action-if-given. If neither option was given, run shell commands
action-if-not-given. The name package indicates another
software package that this program should work with. It should consist
only of alphanumeric characters and dashes.
The option's argument is available to the shell commands
action-if-given in the shell variable withval, which is
actually just the value of the shell variable with_package,
with any `-' characters changed into `_'.
You may use that variable instead, if you wish.
The argument help-string is a description of the option which looks like this:
--with-readline support fancy command line editing
help-string may be more than one line long, if more detail is needed. Just make sure the columns line up in `configure --help'. Avoid tabs in the help string. You'll need to enclose it in `[' and `]' in order to produce the leading spaces.
AC_ARG_WITH that does not
support providing a help string.
If a software package has optional compile-time features, the user can
give configure command line options to specify whether to
compile them. The options have one of these forms:
--enable-feature[=arg] --disable-feature
These options allow users to choose which optional features to build and install. `--enable-feature' options should never make a feature behave differently or cause one feature to replace another. They should only cause parts of the program to be built rather than left out.
The user can give an argument by following the feature name with `=' and the argument. Giving an argument of `no' requests that the feature not be made available. A feature with an argument looks like `--enable-debug=stabs'. If no argument is given, it defaults to `yes'. `--disable-feature' is equivalent to `--enable-feature=no'.
configure scripts do not complain about
`--enable-feature' options that they do not support.
This behavior permits configuring a source tree containing multiple
packages with a top-level configure script when the packages
support different options, without spurious error messages about options
that some of the packages support.
An unfortunate side effect is that option spelling errors are not diagnosed.
No better approach to this problem has been suggested so far.
For each optional feature, `configure.in' should call
AC_ARG_ENABLE to detect whether the configure user asked
to include it. Whether each feature is included or not by default, and
which arguments are valid, is up to you.
configure the option
`--enable-feature' or `--disable-feature', run
shell commands action-if-given. If neither option was given, run
shell commands action-if-not-given. The name feature
indicates an optional user-level facility. It should consist only of
alphanumeric characters and dashes.
The option's argument is available to the shell commands
action-if-given in the shell variable enableval, which is
actually just the value of the shell variable
enable_feature, with any `-' characters changed into
`_'. You may use that variable instead, if you wish. The
help-string argument is like that of AC_ARG_WITH
(see section Working With External Software).
AC_ARG_ENABLE that does not
support providing a help string.
Some software packages require complex site-specific information. Some examples are host names to use for certain services, company names, and email addresses to contact. Since some configuration scripts generated by Metaconfig ask for such information interactively, people sometimes wonder how to get that information in Autoconf-generated configuration scripts, which aren't interactive.
Such site configuration information should be put in a file that is
edited only by users, not by programs. The location of the file
can either be based on the prefix variable, or be a standard
location such as the user's home directory. It could even be specified
by an environment variable. The programs should examine that file at
run time, rather than at compile time. Run time configuration is more
convenient for users and makes the configuration process simpler than
getting the information while configuring. See section `Variables for Installation Directories' in GNU Coding Standards, for more information on where to put data files.
Autoconf supports changing the names of programs when installing them.
In order to use these transformations, `configure.in' must call the
macro AC_ARG_PROGRAM.
program_transform_name a sequence of
sed commands for changing the names of installed programs.
If any of the options described below are given to configure,
program names are transformed accordingly. Otherwise, if
AC_CANONICAL_SYSTEM has been called and a `--target' value
is given that differs from the host type (specified with `--host'
or defaulted by config.sub), the target type followed by a dash
is used as a prefix. Otherwise, no program name transformation is done.
You can specify name transformations by giving configure these
command line options:
--program-prefix=prefix
--program-suffix=suffix
--program-transform-name=expression
sed substitution expression on the names.
These transformations are useful with programs that can be part of a cross-compilation development environment. For example, a cross-assembler running on a Sun 4 configured with `--target=i960-vxworks' is normally installed as `i960-vxworks-as', rather than `as', which could be confused with a native Sun 4 assembler.
You can force a program name to begin with `g', if you don't want
GNU programs installed on your system to shadow other programs with the
same name. For example, if you configure GNU diff with
`--program-prefix=g', then when you run `make install' it is
installed as `/usr/local/bin/gdiff'.
As a more sophisticated example, you could use
--program-transform-name='s/^/g/; s/^gg/g/; s/^gless/less/'
to prepend `g' to most of the program names in a source tree,
excepting those like gdb that already have one and those like
less and lesskey that aren't GNU programs. (That is
assuming that you have a source tree containing those programs that is
set up to use this feature.)
One way to install multiple versions of some programs simultaneously is to append a version number to the name of one or both. For example, if you want to keep Autoconf version 1 around for awhile, you can configure Autoconf version 2 using `--program-suffix=2' to install the programs as `/usr/local/bin/autoconf2', `/usr/local/bin/autoheader2', etc.
Here is how to use the variable program_transform_name in a
`Makefile.in':
transform=@program_transform_name@
install: all
$(INSTALL_PROGRAM) myprog $(bindir)/`echo myprog|sed '$(transform)'`
uninstall:
rm -f $(bindir)/`echo myprog|sed '$(transform)'`
If you have more than one program to install, you can do it in a loop:
PROGRAMS=cp ls rm
install:
for p in $(PROGRAMS); do \
$(INSTALL_PROGRAM) $$p $(bindir)/`echo $$p|sed '$(transform)'`; \
done
uninstall:
for p in $(PROGRAMS); do \
rm -f $(bindir)/`echo $$p|sed '$(transform)'`; \
done
Whether to do the transformations on documentation files (Texinfo or
man) is a tricky question; there seems to be no perfect answer,
due to the several reasons for name transforming. Documentation is not
usually particular to a specific architecture, and Texinfo files do not
conflict with system documentation. But they might conflict with
earlier versions of the same files, and man pages sometimes do
conflict with system documentation. As a compromise, it is probably
best to do name transformations on man pages but not on Texinfo
manuals.
Autoconf-generated configure scripts allow your site to provide
default values for some configuration values. You do this by creating
site- and system-wide initialization files.
If the environment variable CONFIG_SITE is set, configure
uses its value as the name of a shell script to read. Otherwise, it
reads the shell script `prefix/share/config.site' if it exists,
then `prefix/etc/config.site' if it exists. Thus,
settings in machine-specific files override those in machine-independent
ones in case of conflict.
Site files can be arbitrary shell scripts, but only certain kinds of
code are really appropriate to be in them. Because configure
reads any cache file after it has read any site files, a site file can
define a default cache file to be shared between all Autoconf-generated
configure scripts run on that system. If you set a default cache
file in a site file, it is a good idea to also set the output variable
CC in that site file, because the cache file is only valid for a
particular compiler, but many systems have several available.
You can examine or override the value set by a command line option to
configure in a site file; options set shell variables that have
the same names as the options, with any dashes turned into underscores.
The exceptions are that `--without-' and `--disable-' options
are like giving the corresponding `--with-' or `--enable-'
option and the value `no'. Thus, `--cache-file=localcache'
sets the variable cache_file to the value `localcache';
`--enable-warnings=no' or `--disable-warnings' sets the variable
enable_warnings to the value `no'; `--prefix=/usr' sets the
variable prefix to the value `/usr'; etc.
Site files are also good places to set default values for other output
variables, such as CFLAGS, if you need to give them non-default
values: anything you would normally do, repetitively, on the command
line. If you use non-default values for prefix or
exec_prefix (wherever you locate the site file), you can set them
in the site file if you specify it with the CONFIG_SITE
environment variable.
You can set some cache values in the site file itself. Doing this is
useful if you are cross-compiling, so it is impossible to check features
that require running a test program. You could "prime the cache" by
setting those values correctly for that system in
`prefix/etc/config.site'. To find out the names of the cache
variables you need to set, look for shell variables with `_cv_' in
their names in the affected configure scripts, or in the Autoconf
m4 source code for those macros.
The cache file is careful to not override any variables set in the site
files. Similarly, you should not override command-line options in the
site files. Your code should check that variables such as prefix
and cache_file have their default values (as set near the top of
configure) before changing them.
Here is a sample file `/usr/share/local/gnu/share/config.site'. The
command `configure --prefix=/usr/share/local/gnu' would read this
file (if CONFIG_SITE is not set to a different file).
# config.site for configure
#
# Change some defaults.
test "$prefix" = NONE && prefix=/usr/share/local/gnu
test "$exec_prefix" = NONE && exec_prefix=/usr/local/gnu
test "$sharedstatedir" = '${prefix}/com' && sharedstatedir=/var
test "$localstatedir" = '${prefix}/var' && localstatedir=/var
#
# Give Autoconf 2.x generated configure scripts a shared default
# cache file for feature test results, architecture-specific.
if test "$cache_file" = ./config.cache; then
cache_file="$prefix/var/config.cache"
# A cache file is only valid for one C compiler.
CC=gcc
fi
configure Scripts
Below are instructions on how to configure a package that uses a
configure script, suitable for inclusion as an `INSTALL'
file in the package. A plain-text version of `INSTALL' which you
may use comes with Autoconf.
The configure script creates a file named `config.status'
which describes which configuration options were specified when the
package was last configured. This file is a shell script which,
if run, will recreate the same configuration.
You can give `config.status' the `--recheck' option to update
itself. This option is useful if you change configure, so that
the results of some tests might be different from the previous run. The
`--recheck' option re-runs configure with the same arguments
you used before, plus the `--no-create' option, which prevent
configure from running `config.status' and creating
`Makefile' and other files, and the `--no-recursion' option,
which prevents configure from running other configure
scripts in subdirectories. (This is so other `Makefile' rules can
run `config.status' when it changes; see section Automatic Remaking,
for an example).
`config.status' also accepts the options `--help', which
prints a summary of the options to `config.status', and
`--version', which prints the version of Autoconf used to create
the configure script that generated `config.status'.
`config.status' checks several optional environment variables that can alter its behavior:
configure for the `--recheck'
option. It must be Bourne-compatible. The default is `/bin/sh'.
configure
scripts shouldn't be merged because they are maintained separately.
The following variables provide one way for separately distributed
packages to share the values computed by configure. Doing so can
be useful if some of the packages need a superset of the features that
one of them, perhaps a common library, does. These variables allow a
`config.status' file to create files other than the ones that its
`configure.in' specifies, so it can be used for a different package.
AC_OUTPUT in `configure.in'.
#define statements.
The default is the arguments given to AC_CONFIG_HEADER; if that
macro was not called, `config.status' ignores this variable.
These variables also allow you to write `Makefile' rules that regenerate only some of the files. For example, in the dependencies given above (see section Automatic Remaking), `config.status' is run twice when `configure.in' has changed. If that bothers you, you can make each run only regenerate the files for that rule:
config.h: stamp-h
stamp-h: config.h.in config.status
CONFIG_FILES= CONFIG_HEADERS=config.h ./config.status
echo > stamp-h
Makefile: Makefile.in config.status
CONFIG_FILES=Makefile CONFIG_HEADERS= ./config.status
(If `configure.in' does not call AC_CONFIG_HEADER, there is
no need to set CONFIG_HEADERS in the make rules.)
Several questions about Autoconf come up occasionally. Here some of them are addressed.
configure Scripts
What are the restrictions on distributing configure
scripts that Autoconf generates? How does that affect my
programs that use them?
There are no restrictions on how the configuration scripts that Autoconf produces may be distributed or used. In Autoconf version 1, they were covered by the GNU General Public License. We still encourage software authors to distribute their work under terms like those of the GPL, but doing so is not required to use Autoconf.
Of the other files that might be used with configure,
`config.h.in' is under whatever copyright you use for your
`configure.in', since it is derived from that file and from the
public domain file `acconfig.h'. `config.sub' and
`config.guess' have an exception to the GPL when they are used with
an Autoconf-generated configure script, which permits you to
distribute them under the same terms as the rest of your package.
`install-sh' is from the X Consortium and is not copyrighted.
m4?
Why does Autoconf require GNU m4?
Many m4 implementations have hard-coded limitations on the size
and number of macros, which Autoconf exceeds. They also lack several
builtin macros that it would be difficult to get along without in a
sophisticated application like Autoconf, including:
builtin indir patsubst __file__ __line__
Since only software maintainers need to use Autoconf, and since GNU
m4 is simple to configure and install, it seems reasonable to
require GNU m4 to be installed also. Many maintainers of GNU and
other free software already have most of the GNU utilities installed,
since they prefer them.
If Autoconf requires GNUm4and GNUm4has an Autoconfconfigurescript, how do I bootstrap? It seems like a chicken and egg problem!
This is a misunderstanding. Although GNU m4 does come with a
configure script produced by Autoconf, Autoconf is not required
in order to run the script and install GNU m4. Autoconf is only
required if you want to change the m4 configure script,
which few people have to do (mainly its maintainer).
Why not use Imake instead of configure scripts?
Several people have written addressing this question, so I include adaptations of their explanations here.
The following answer is based on one written by Richard Pixley:
Autoconf generated scripts frequently work on machines which it has never been set up to handle before. That is, it does a good job of inferring a configuration for a new system. Imake cannot do this.
Imake uses a common database of host specific data. For X11, this makes sense because the distribution is made as a collection of tools, by one central authority who has control over the database.
GNU tools are not released this way. Each GNU tool has a maintainer; these maintainers are scattered across the world. Using a common database would be a maintenance nightmare. Autoconf may appear to be this kind of database, but in fact it is not. Instead of listing host dependencies, it lists program requirements.
If you view the GNU suite as a collection of native tools, then the problems are similar. But the GNU development tools can be configured as cross tools in almost any host+target permutation. All of these configurations can be installed concurrently. They can even be configured to share host independent files across hosts. Imake doesn't address these issues.
Imake templates are a form of standardization. The GNU coding standards address the same issues without necessarily imposing the same restrictions.
Here is some further explanation, written by Per Bothner:
One of the advantages of Imake is that it easy to generate large
Makefiles using cpp's `#include' and macro mechanisms.
However, cpp is not programmable: it has limited conditional
facilities, and no looping. And cpp cannot inspect its
environment.
All of these problems are solved by using sh instead of
cpp. The shell is fully programmable, has macro substitution,
can execute (or source) other shell scripts, and can inspect its
environment.
Paul Eggert elaborates more:
With Autoconf, installers need not assume that Imake itself is already installed and working well. This may not seem like much of an advantage to people who are accustomed to Imake. But on many hosts Imake is not installed or the default installation is not working well, and requiring Imake to install a package hinders the acceptance of that package on those hosts. For example, the Imake template and configuration files might not be installed properly on a host, or the Imake build procedure might wrongly assume that all source files are in one big directory tree, or the Imake configuration might assume one compiler whereas the package or the installer needs to use another, or there might be a version mismatch between the Imake expected by the package and the Imake supported by the host. These problems are much rarer with Autoconf, where each package comes with its own independent configuration processor.
Also, Imake often suffers from unexpected interactions between
make and the installer's C preprocessor. The fundamental problem
here is that the C preprocessor was designed to preprocess C programs,
not `Makefile's. This is much less of a problem with Autoconf,
which uses the general-purpose preprocessor m4, and where the
package's author (rather than the installer) does the preprocessing in a
standard way.
Finally, Mark Eichin notes:
Imake isn't all that extensible, either. In order to add new features to Imake, you need to provide your own project template, and duplicate most of the features of the existing one. This means that for a sophisticated project, using the vendor-provided Imake templates fails to provide any leverage--since they don't cover anything that your own project needs (unless it is an X11 program).
On the other side, though:
The one advantage that Imake has over configure:
`Imakefile's tend to be much shorter (likewise, less redundant)
than `Makefile.in's. There is a fix to this, however--at least
for the Kerberos V5 tree, we've modified things to call in common
`post.in' and `pre.in' `Makefile' fragments for the
entire tree. This means that a lot of common things don't have to be
duplicated, even though they normally are in configure setups.
Autoconf version 2 is mostly backward compatible with version 1.
However, it introduces better ways to do some things, and doesn't
support some of the ugly things in version 1. So, depending on how
sophisticated your `configure.in' files are, you might have to do
some manual work in order to upgrade to version 2. This chapter points
out some problems to watch for when upgrading. Also, perhaps your
configure scripts could benefit from some of the new features in
version 2; the changes are summarized in the file `NEWS' in the
Autoconf distribution.
First, make sure you have GNU m4 version 1.1 or higher installed,
preferably 1.3 or higher. Versions before 1.1 have bugs that prevent
them from working with Autoconf version 2. Versions 1.3 and later are
much faster than earlier versions, because as of version 1.3, GNU
m4 has a more efficient implementation of diversions and can
freeze its internal state in a file that it can read back quickly.
If you have an `aclocal.m4' installed with Autoconf (as opposed to
in a particular package's source directory), you must rename it to
`acsite.m4'. See section Using autoconf to Create configure.
If you distribute `install.sh' with your package, rename it to
`install-sh' so make builtin rules won't inadvertently
create a file called `install' from it. AC_PROG_INSTALL
looks for the script under both names, but it is best to use the new name.
If you were using `config.h.top' or `config.h.bot', you still
can, but you will have less clutter if you merge them into
`acconfig.h'. See section Using autoheader to Create `config.h.in'.
Add `@CFLAGS@', `@CPPFLAGS@', and `@LDFLAGS@' in
your `Makefile.in' files, so they can take advantage of the values
of those variables in the environment when configure is run.
Doing this isn't necessary, but it's a convenience for users.
Also add `@configure_input@' in a comment to each non-`Makefile'
input file for
AC_OUTPUT, so that the output files will contain a comment saying
they were produced by configure. Automatically selecting the
right comment syntax for all the kinds of files that people call
AC_OUTPUT on became too much work.
Add `config.log' and `config.cache' to the list of files you
remove in distclean targets.
If you have the following in `Makefile.in':
prefix = /usr/local
exec_prefix = ${prefix}
you must change it to:
prefix = @prefix@ exec_prefix = @exec_prefix@
The old behavior of replacing those variables without `@' characters around them has been removed.
Many of the macros were renamed in Autoconf version 2. You can still
use the old names, but the new ones are clearer, and it's easier to find
the documentation for them. See section Old Macro Names, for a table showing
the new names for the old macros. Use the autoupdate program to
convert your `configure.in' to using the new macro names.
See section Using autoupdate to Modernize configure.
Some macros have been superseded by similar ones that do the job better,
but are not call-compatible. If you get warnings about calling obsolete
macros while running autoconf, you may safely ignore them, but
your configure script will generally work better if you follow
the advice it prints about what to replace the obsolete macros with. In
particular, the mechanism for reporting the results of tests has
changed. If you were using echo or AC_VERBOSE (perhaps
via AC_COMPILE_CHECK), your configure script's output will
look better if you switch to AC_MSG_CHECKING and
AC_MSG_RESULT. See section Printing Messages. Those macros work best
in conjunction with cache variables. See section Caching Results.
autoupdate to Modernize configure
The autoupdate program updates a `configure.in' file that
calls Autoconf macros by their old names to use the current macro names.
In version 2 of Autoconf, most of the macros were renamed to use a more
uniform and descriptive naming scheme. See section Macro Names, for a
description of the new scheme. Although the old names still work
(see section Old Macro Names, for a list of the old macro names and the
corresponding new names), you can make your `configure.in' files
more readable and make it easier to use the current Autoconf
documentation if you update them to use the new macro names.
If given no arguments, autoupdate updates `configure.in',
backing up the original version with the suffix `~' (or the value
of the environment variable SIMPLE_BACKUP_SUFFIX, if that is
set). If you give autoupdate an argument, it reads that file
instead of `configure.in' and writes the updated file to the
standard output.
autoupdate accepts the following options:
--help
-h
--macrodir=dir
-m dir
AC_MACRODIR
environment variable to a directory; this option overrides the
environment variable.
--version
autoupdate and exit.
If you were checking the results of previous tests by examining the
shell variable DEFS, you need to switch to checking the values of
the cache variables for those tests. DEFS no longer exists while
configure is running; it is only created when generating output
files. This difference from version 1 is because properly quoting the
contents of that variable turned out to be too cumbersome and
inefficient to do every time AC_DEFINE is called. See section Cache Variable Names.
For example, here is a `configure.in' fragment written for Autoconf version 1:
AC_HAVE_FUNCS(syslog)
case "$DEFS" in
*-DHAVE_SYSLOG*) ;;
*) # syslog is not in the default libraries. See if it's in some other.
saved_LIBS="$LIBS"
for lib in bsd socket inet; do
AC_CHECKING(for syslog in -l$lib)
LIBS="$saved_LIBS -l$lib"
AC_HAVE_FUNCS(syslog)
case "$DEFS" in
*-DHAVE_SYSLOG*) break ;;
*) ;;
esac
LIBS="$saved_LIBS"
done ;;
esac
Here is a way to write it for version 2:
AC_CHECK_FUNCS(syslog)
if test $ac_cv_func_syslog = no; then
# syslog is not in the default libraries. See if it's in some other.
for lib in bsd socket inet; do
AC_CHECK_LIB($lib, syslog, [AC_DEFINE(HAVE_SYSLOG)
LIBS="$LIBS $lib"; break])
done
fi
If you were working around bugs in AC_DEFINE_UNQUOTED by adding
backslashes before quotes, you need to remove them. It now works
predictably, and does not treat quotes (except backquotes) specially.
See section Setting Output Variables.
All of the boolean shell variables set by Autoconf macros now use `yes' for the true value. Most of them use `no' for false, though for backward compatibility some use the empty string instead. If you were relying on a shell variable being set to something like 1 or `t' for true, you need to change your tests.
When defining your own macros, you should now use AC_DEFUN
instead of define. AC_DEFUN automatically calls
AC_PROVIDE and ensures that macros called via AC_REQUIRE
do not interrupt other macros, to prevent nested `checking...'
messages on the screen. There's no actual harm in continuing to use the
older way, but it's less convenient and attractive. See section Macro Definitions.
You probably looked at the macros that came with Autoconf as a guide for how to do things. It would be a good idea to take a look at the new versions of them, as the style is somewhat improved and they take advantage of some new features.
If you were doing tricky things with undocumented Autoconf internals (macros, variables, diversions), check whether you need to change anything to account for changes that have been made. Perhaps you can even use an officially supported technique in version 2 instead of kludging. Or perhaps not.
To speed up your locally written feature tests, add caching to them. See whether any of your tests are of general enough usefulness to encapsulate into macros that you can share.
You may be wondering, Why was Autoconf originally written? How did it get into its present form? (Why does it look like gorilla spit?) If you're not wondering, then this chapter contains no information useful to you, and you might as well skip it. If you are wondering, then let there be light...
In June 1991 I was maintaining many of the GNU utilities for the Free
Software Foundation. As they were ported to more platforms and more
programs were added, the number of `-D' options that users had to
select in the `Makefile' (around 20) became burdensome. Especially
for me--I had to test each new release on a bunch of different systems.
So I wrote a little shell script to guess some of the correct settings
for the fileutils package, and released it as part of fileutils 2.0.
That configure script worked well enough that the next month I
adapted it (by hand) to create similar configure scripts for
several other GNU utilities packages. Brian Berliner also adapted one
of my scripts for his CVS revision control system.
Later that summer, I learned that Richard Stallman and Richard Pixley
were developing similar scripts to use in the GNU compiler tools; so I
adapted my configure scripts to support their evolving interface:
using the file name `Makefile.in' as the templates; adding
`+srcdir', the first option (of many); and creating
`config.status' files.
As I got feedback from users, I incorporated many improvements, using
Emacs to search and replace, cut and paste, similar changes in each of
the scripts. As I adapted more GNU utilities packages to use
configure scripts, updating them all by hand became impractical.
Rich Murphey, the maintainer of the GNU graphics utilities, sent me mail
saying that the configure scripts were great, and asking if I had
a tool for generating them that I could send him. No, I thought, but
I should! So I started to work out how to generate them. And the
journey from the slavery of hand-written configure scripts to the
abundance and ease of Autoconf began.
Cygnus configure, which was being developed at around that time,
is table driven; it is meant to deal mainly with a discrete number of
system types with a small number of mainly unguessable features (such as
details of the object file format). The automatic configuration system
that Brian Fox had developed for Bash takes a similar approach. For
general use, it seems to me a hopeless cause to try to maintain an
up-to-date database of which features each variant of each operating
system has. It's easier and more reliable to check for most features on
the fly--especially on hybrid systems that people have hacked on
locally or that have patches from vendors installed.
I considered using an architecture similar to that of Cygnus
configure, where there is a single configure script that
reads pieces of `configure.in' when run. But I didn't want to have
to distribute all of the feature tests with every package, so I settled
on having a different configure made from each
`configure.in' by a preprocessor. That approach also offered more
control and flexibility.
I looked briefly into using the Metaconfig package, by Larry Wall,
Harlan Stenn, and Raphael Manfredi, but I decided not to for several
reasons. The Configure scripts it produces are interactive,
which I find quite inconvenient; I didn't like the ways it checked for
some features (such as library functions); I didn't know that it was
still being maintained, and the Configure scripts I had
seen didn't work on many modern systems (such as System V R4 and NeXT);
it wasn't very flexible in what it could do in response to a feature's
presence or absence; I found it confusing to learn; and it was too big
and complex for my needs (I didn't realize then how much Autoconf would
eventually have to grow).
I considered using Perl to generate my style of configure scripts,
but decided that m4 was better suited to the job of simple
textual substitutions: it gets in the way less, because output is
implicit. Plus, everyone already has it. (Initially I didn't rely on
the GNU extensions to m4.) Also, some of my friends at the
University of Maryland had recently been putting m4 front ends on
several programs, including tvtwm, and I was interested in trying
out a new language.
Since my configure scripts determine the system's capabilities
automatically, with no interactive user intervention, I decided to call
the program that generates them Autoconfig. But with a version number
tacked on, that name would be too long for old UNIX file systems, so
I shortened it to Autoconf.
In the fall of 1991 I called together a group of fellow questers after
the Holy Grail of portability (er, that is, alpha testers) to give me
feedback as I encapsulated pieces of my handwritten scripts in m4
macros and continued to add features and improve the techniques used in
the checks. Prominent among the testers were
Pinard, who came up with the idea of making an `autoconf' shell
script to run m4 and check for unresolved macro calls; Richard
Pixley, who suggested running the compiler instead of searching the file
system to find include files and symbols, for more accurate results;
Karl Berry, who got Autoconf to configure TeX and added the
macro index to the documentation; and Ian Taylor, who added support for
creating a C header file as an alternative to putting `-D' options
in a `Makefile', so he could use Autoconf for his UUCP package. The
alpha testers cheerfully adjusted their files again and again as the
names and calling conventions of the Autoconf macros changed from
release to release. They all contributed many specific checks, great
ideas, and bug fixes.
In July 1992, after months of alpha testing, I released Autoconf 1.0,
and converted many GNU packages to use it. I was surprised by how
positive the reaction to it was. More people started using it than I
could keep track of, including people working on software that wasn't
part of the GNU Project (such as TCL, FSP, and Kerberos V5).
Autoconf continued to improve rapidly, as many people using the
configure scripts reported problems they encountered.
Autoconf turned out to be a good torture test for m4
implementations. UNIX m4 started to dump core because of the
length of the macros that Autoconf defined, and several bugs showed up
in GNU m4 as well. Eventually, we realized that we needed to use
some features that only GNU m4 has. 4.3BSD m4, in
particular, has an impoverished set of builtin macros; the System V
version is better, but still doesn't provide everything we need.
More development occurred as people put Autoconf under more stresses
(and to uses I hadn't anticipated). Karl Berry added checks for X11.
david zuhn contributed C++ support.
Pinard made it diagnose invalid arguments. Jim Blandy bravely coerced
it into configuring GNU Emacs, laying the groundwork for several later
improvements. Roland McGrath got it to configure the GNU C Library,
wrote the autoheader script to automate the creation of C header
file templates, and added a `--verbose' option to configure.
Noah Friedman added the `--macrodir' option and AC_MACRODIR
environment variable. (He also coined the term autoconfiscate to
mean "adapt a software package to use Autoconf".) Roland and Noah
improved the quoting protection in AC_DEFINE and fixed many bugs,
especially when I got sick of dealing with portability problems from
February through June, 1993.
A long wish list for major features had accumulated, and the effect of
several years of patching by various people had left some residual
cruft. In April 1994, while working for Cygnus Support, I began a major
revision of Autoconf. I added most of the features of the Cygnus
configure that Autoconf had lacked, largely by adapting the
relevant parts of Cygnus configure with the help of david zuhn
and Ken Raeburn. These features include support for using
`config.sub', `config.guess', `--host', and
`--target'; making links to files; and running configure
scripts in subdirectories. Adding these features enabled Ken to convert
GNU as, and Rob Savoye to convert DejaGNU, to using Autoconf.
I added more features in response to other peoples' requests. Many
people had asked for configure scripts to share the results of
the checks between runs, because (particularly when configuring a large
source tree, like Cygnus does) they were frustratingly slow. Mike
Haertel suggested adding site-specific initialization scripts. People
distributing software that had to unpack on MS-DOS asked for a way to
override the `.in' extension on the file names, which produced file
names like `config.h.in' containing two dots. Jim Avera did an
extensive examination of the problems with quoting in AC_DEFINE
and AC_SUBST; his insights led to significant improvements.
Richard Stallman asked that compiler output be sent to `config.log'
instead of `/dev/null', to help people debug the Emacs
configure script.
I made some other changes because of my dissatisfaction with the quality
of the program. I made the messages showing results of the checks less
ambiguous, always printing a result. I regularized the names of the
macros and cleaned up coding style inconsistencies. I added some
auxiliary utilities that I had developed to help convert source code
packages to use Autoconf. With the help of
Pinard, I made the macros not interrupt each others' messages.
(That feature revealed some performance bottlenecks in GNU m4,
which he hastily corrected!)
I reorganized the documentation around problems people want to solve.
And I began a testsuite, because experience
had shown that Autoconf has a pronounced tendency to regress when we
change it.
Again, several alpha testers gave invaluable feedback, especially Pinard, Jim Meyering, Karl Berry, Rob Savoye, Ken Raeburn, and Mark Eichin.
Finally, version 2.0 was ready. And there was much rejoicing. (And I have free time again. I think. Yeah, right.)
In version 2 of Autoconf, most of the macros were renamed to use a more
uniform and descriptive naming scheme. Here are the old names of the
macros that were renamed, followed by the current names of those macros.
Although the old names are still accepted by the autoconf program
for backward compatibility, the old names are considered obsolete.
See section Macro Names, for a description of the new naming scheme.
AC_ALLOCA
AC_FUNC_ALLOCA
AC_ARG_ARRAY
AC_CHAR_UNSIGNED
AC_C_CHAR_UNSIGNED
AC_CONST
AC_C_CONST
AC_CROSS_CHECK
AC_C_CROSS
AC_ERROR
AC_MSG_ERROR
AC_FIND_X
AC_PATH_X
AC_FIND_XTRA
AC_PATH_XTRA
AC_FUNC_CHECK
AC_CHECK_FUNC
AC_GCC_TRADITIONAL
AC_PROG_GCC_TRADITIONAL
AC_GETGROUPS_T
AC_TYPE_GETGROUPS
AC_GETLOADAVG
AC_FUNC_GETLOADAVG
AC_HAVE_FUNCS
AC_CHECK_FUNCS
AC_HAVE_HEADERS
AC_CHECK_HEADERS
AC_HAVE_POUNDBANG
AC_SYS_INTERPRETER (different calling convention)
AC_HEADER_CHECK
AC_CHECK_HEADER
AC_HEADER_EGREP
AC_EGREP_HEADER
AC_INLINE
AC_C_INLINE
AC_LN_S
AC_PROG_LN_S
AC_LONG_DOUBLE
AC_C_LONG_DOUBLE
AC_LONG_FILE_NAMES
AC_SYS_LONG_FILE_NAMES
AC_MAJOR_HEADER
AC_HEADER_MAJOR
AC_MINUS_C_MINUS_O
AC_PROG_CC_C_O
AC_MMAP
AC_FUNC_MMAP
AC_MODE_T
AC_TYPE_MODE_T
AC_OFF_T
AC_TYPE_OFF_T
AC_PID_T
AC_TYPE_PID_T
AC_PREFIX
AC_PREFIX_PROGRAM
AC_PROGRAMS_CHECK
AC_CHECK_PROGS
AC_PROGRAMS_PATH
AC_PATH_PROGS
AC_PROGRAM_CHECK
AC_CHECK_PROG
AC_PROGRAM_EGREP
AC_EGREP_CPP
AC_PROGRAM_PATH
AC_PATH_PROG
AC_REMOTE_TAPE
AC_RESTARTABLE_SYSCALLS
AC_SYS_RESTARTABLE_SYSCALLS
AC_RETSIGTYPE
AC_TYPE_SIGNAL
AC_RSH
AC_SETVBUF_REVERSED
AC_FUNC_SETVBUF_REVERSED
AC_SET_MAKE
AC_PROG_MAKE_SET
AC_SIZEOF_TYPE
AC_CHECK_SIZEOF
AC_SIZE_T
AC_TYPE_SIZE_T
AC_STAT_MACROS_BROKEN
AC_HEADER_STAT
AC_STDC_HEADERS
AC_HEADER_STDC
AC_STRCOLL
AC_FUNC_STRCOLL
AC_ST_BLKSIZE
AC_STRUCT_ST_BLKSIZE
AC_ST_BLOCKS
AC_STRUCT_ST_BLOCKS
AC_ST_RDEV
AC_STRUCT_ST_RDEV
AC_SYS_SIGLIST_DECLARED
AC_DECL_SYS_SIGLIST
AC_TEST_CPP
AC_TRY_CPP
AC_TEST_PROGRAM
AC_TRY_RUN
AC_TIMEZONE
AC_STRUCT_TIMEZONE
AC_TIME_WITH_SYS_TIME
AC_HEADER_TIME
AC_UID_T
AC_TYPE_UID_T
AC_UTIME_NULL
AC_FUNC_UTIME_NULL
AC_VFORK
AC_FUNC_VFORK
AC_VPRINTF
AC_FUNC_VPRINTF
AC_WAIT3
AC_FUNC_WAIT3
AC_WARN
AC_MSG_WARN
AC_WORDS_BIGENDIAN
AC_C_BIGENDIAN
AC_YYTEXT_POINTER
AC_DECL_YYTEXT
This is an alphabetical list of the environment variables that Autoconf checks.
This is an alphabetical list of the variables that Autoconf can substitute into files that it creates, typically one or more `Makefile's. See section Setting Output Variables, for more information on how this is done.
Jump to: a - b - c - d - e - f - h - i - k - l - m - n - o - p - r - s - t - x - y
This is an alphabetical list of the C preprocessor symbols that the
Autoconf macros define. To work with Autoconf, C source code needs to
use these names in #if directives.
Jump to: _ - c - d - f - g - h - i - l - m - n - o - p - r - s - t - u - v - w - y
This is an alphabetical list of the Autoconf macros. To make the list easier to use, the macros are listed without their preceding `AC_'.
Jump to: a - b - c - d - e - f - g - h - i - l - m - o - p - r - s - t - u - v - w - x - y
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