START-INFO-DIR-ENTRY * Autoconf: (autoconf). Create source code configuration scripts. END-INFO-DIR-ENTRY Autoconf: Creating Automatic Configuration Scripts, by David MacKenzie. This file documents the GNU Autoconf package for creating scripts to configure source code packages using templates and an `m4' macro package. Copyright (C) 1992, 1993, 1994, 1995, 1996, 1998 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. This file documents the GNU Autoconf package for creating scripts to configure source code packages using templates and an `m4' macro package. This is edition 2.13, for Autoconf version 2.13. Introduction ************ 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 (*note 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. *Note Upgrading::, for information about upgrading from version 1. *Note History::, for the story of Autoconf's development. *Note Questions::, 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'. Making `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: * one or more `Makefile' files, one in each subdirectory of the package (*note Makefile Substitutions::.); * optionally, a C header file, the name of which is configurable, containing `#define' directives (*note Configuration Headers::.); * a shell script called `config.status' that, when run, will recreate the files listed above (*note Invoking config.status::.); * a shell script called `config.cache' that saves the results of running many of the tests (*note Cache Files::.); * a file called `config.log' containing any messages produced by compilers, to help debugging if `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 ---' Writing `configure.in' ====================== 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 *Note Existing Tests::, for their descriptions. For most other features, you can use Autoconf template macros to produce custom checks; see *Note 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' (*note Invoking autoscan::., 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 (*note Output::.). 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 (*note 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 services `AC_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. Using `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' (*note Configuration Headers::.). You might also have to change or add some `#if' directives to your program in order to make it work with Autoconf (*note Invoking ifnames::., 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' Print a summary of the command line options and exit. `--macrodir=DIR' Look for the data files in directory DIR instead of the default installation directory. You can also set the `AC_MACRODIR' environment variable to a directory; this option overrides the environment variable. `--verbose' Print the names of the files it examines and the potentially interesting symbols it finds in them. This output can be voluminous. `--version' Print the version number of Autoconf and exit. Using `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' (*note Invoking autoscan::.). `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' Print a summary of the command line options and exit. `--macrodir=DIR' `-m DIR' Look for the Autoconf macro files in directory DIR instead of the default installation directory. Only used to get the version number. You can also set the `AC_MACRODIR' environment variable to a directory; this option overrides the environment variable. `--version' Print the version number of Autoconf and exit. Using `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 (*note 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' Print a summary of the command line options and exit. `--localdir=DIR' `-l DIR' Look for the package file `aclocal.m4' in directory DIR instead of in the current directory. `--macrodir=DIR' `-m DIR' Look for the installed macro files in directory DIR. You can also set the `AC_MACRODIR' environment variable to a directory; this option overrides the environment variable. `--version' Print the version number of Autoconf and exit. Using `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. *Note 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' Print a summary of the command line options and exit. `--force' `-f' Remake even `configure' scripts and configuration headers that are newer than their input files (`configure.in' and, if present, `aclocal.m4'). `--localdir=DIR' `-l DIR' Have `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' Look for the Autoconf macro files in directory DIR instead of the default installation directory. You can also set the `AC_MACRODIR' environment variable to a directory; this option overrides the environment variable. `--verbose' Print the name of each directory where `autoreconf' runs `autoconf' (and `autoheader', if appropriate). `--version' Print the version number of Autoconf and exit. Initialization and Output Files ******************************* 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. Finding `configure' Input ========================= Every `configure' script must call `AC_INIT' before doing anything else. The only other required macro is `AC_OUTPUT' (*note Output::.). - Macro: AC_INIT (UNIQUE-FILE-IN-SOURCE-DIR) Process any command-line arguments and find the source code directory. UNIQUE-FILE-IN-SOURCE-DIR is some file that is in the package's source directory; `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. *Note Invoking configure::, 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. - Macro: AC_CONFIG_AUX_DIR(DIR) Use the `install-sh', `config.sub', `config.guess', and Cygnus `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'. Creating Output Files ===================== 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' (*note Input::.). - Macro: AC_OUTPUT ([FILE... [, EXTRA-CMDS [, INIT-CMDS]]]) Create output files. Call this macro once, at the end of `configure.in'. The FILE... argument is a whitespace-separated list of output files; it may be empty. This macro creates each file `FILE' by copying an input file (by default named `FILE.in'), substituting the output variable values. *Note Makefile Substitutions::, for more information on using output variables. *Note Setting Output Variables::, for more information on creating them. This macro creates the directory that the file is in if it doesn't exist (but not the parents of that directory). Usually, `Makefile's are created this way, but other files, such as `.gdbinit', can be specified as well. 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. - Macro: AC_OUTPUT_COMMANDS (EXTRA-CMDS [, INIT-CMDS]) Specify additional shell commands to run at the end of `config.status', and shell commands to initialize any variables from `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. - Macro: AC_PROG_MAKE_SET If `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@ Substitutions in Makefiles ========================== 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. *Note 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. *Note Makefile Conventions: (standards)Makefile Conventions, for more information on what to put in `Makefile's. Preset Output Variables ----------------------- 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. *Note Output Variable Index::, for a complete list of output variables. Here is what each of the preset ones contains. *Note Variables for Installation Directories: (standards)Directory Variables, for more information about the variables with names that end in `dir'. - Variable: bindir The directory for installing executables that users run. - Variable: configure_input A comment saying that the file was generated automatically by `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. - Variable: datadir The directory for installing read-only architecture-independent data. - Variable: exec_prefix The installation prefix for architecture-dependent files. - Variable: includedir The directory for installing C header files. - Variable: infodir The directory for installing documentation in Info format. - Variable: libdir The directory for installing object code libraries. - Variable: libexecdir The directory for installing executables that other programs run. - Variable: localstatedir The directory for installing modifiable single-machine data. - Variable: mandir The top-level directory for installing documentation in man format. - Variable: oldincludedir The directory for installing C header files for non-gcc compilers. - Variable: prefix The installation prefix for architecture-independent files. - Variable: sbindir The directory for installing executables that system administrators run. - Variable: sharedstatedir The directory for installing modifiable architecture-independent data. - Variable: srcdir The directory that contains the source code for that `Makefile'. - Variable: sysconfdir The directory for installing read-only single-machine data. - Variable: top_srcdir The top-level source code directory for the package. In the top-level directory, this is the same as `srcdir'. - Variable: CFLAGS Debugging and optimization options for the C compiler. If it is not set in the environment when `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. - Variable: CPPFLAGS Header file search directory (`-IDIR') and any other miscellaneous options for the C preprocessor and compiler. If it is not set in the environment when `configure' runs, the default value is empty. `configure' uses this variable when compiling or preprocessing programs to test for C features. - Variable: CXXFLAGS Debugging and optimization options for the C++ compiler. If it is not set in the environment when `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. - Variable: FFLAGS Debugging and optimization options for the Fortran 77 compiler. If it is not set in the environment when `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. - Variable: DEFS `-D' options to pass to the C compiler. If `AC_CONFIG_HEADER' is called, `configure' replaces `@DEFS@' with `-DHAVE_CONFIG_H' instead (*note Configuration Headers::.). This variable is not defined while `configure' is performing its tests, only when creating the output files. *Note Setting Output Variables::, for how to check the results of previous tests. - Variable: LDFLAGS Stripping (`-s') and any other miscellaneous options for the linker. If it is not set in the environment when `configure' runs, the default value is empty. `configure' uses this variable when linking programs to test for C features. - Variable: LIBS `-l' and `-L' options to pass to the linker. Build Directories ----------------- 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) $(srcdir)/time.texinfo Automatic Remaking ------------------ You can put rules like the following in the top-level `Makefile.in' for a package to automatically update the configuration information when you change the configuration files. This example includes all of the optional files, such as `aclocal.m4' and those related to configuration header files. Omit from the `Makefile.in' rules any of these files that your package does not use. The `${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. *Note Output::, for more information about `AC_OUTPUT'. *Note Invoking config.status::, for more examples of handling configuration-related dependencies. Configuration Header Files ========================== 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 ' 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. - Macro: AC_CONFIG_HEADER (HEADER-TO-CREATE ...) Make `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. Configuration Header Templates ------------------------------ 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 Using `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 them from a file, since the possible symbols are effectively limitless. 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' Print a summary of the command line options and exit. `--localdir=DIR' `-l DIR' Look for the package files `aclocal.m4' and `acconfig.h' (but not `FILE.top' and `FILE.bot') in directory DIR instead of in the current directory. `--macrodir=DIR' `-m DIR' Look for the installed macro files and `acconfig.h' in directory DIR. You can also set the `AC_MACRODIR' environment variable to a directory; this option overrides the environment variable. `--version' Print the version number of Autoconf and exit. Configuring Other Packages in Subdirectories ============================================ 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. - Macro: AC_CONFIG_SUBDIRS (DIR ...) Make `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. Default Prefix ============== 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. - Macro: AC_PREFIX_DEFAULT (PREFIX) Set the default installation prefix to PREFIX instead of `/usr/local'. 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'. - Macro: AC_PREFIX_PROGRAM (PROGRAM) If the user did not specify an installation prefix (using the `--prefix' option), guess a value for it by looking for PROGRAM in `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'. Version Numbers in `configure' ============================== The following macros manage version numbers for `configure' scripts. Using them is optional. - Macro: AC_PREREQ (VERSION) Ensure that a recent enough version of Autoconf is being used. If the version of Autoconf being used to create `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. - Macro: AC_REVISION (REVISION-INFO) Copy revision stamp REVISION-INFO into the `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: 1.30 $)dnl produces this in `configure': #! /bin/sh # From configure.in Revision: 1.30 Existing Tests ************** These macros test for particular system features that packages might need or want to use. If you need to test for a kind of feature that none of these macros check for, you can probably do it by calling primitive test macros with appropriate arguments (*note 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 (*note Caching Results::.). Some of these macros set output variables. *Note Makefile Substitutions::, 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". *Note Defining Symbols::, for how to get those symbol definitions into your program. Alternative Programs ==================== These macros check for the presence or behavior of particular programs. They are used to choose between several alternative programs and to decide what to do once one has been chosen. If there is no macro specifically defined to check for a program you need, and you don't need to check for any special properties of it, then you can use one of the general program check macros. Particular Program Checks ------------------------- These macros check for particular programs--whether they exist, and in some cases whether they support certain features. - Macro: AC_DECL_YYTEXT Define `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. - Macro: AC_PROG_AWK Check for `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. - Macro: AC_PROG_CC Determine a C compiler to use. If `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). *Note Manual Configuration::, for more on support for cross compiling. - Macro: AC_PROG_CC_C_O If the C compiler does not accept the `-c' and `-o' options simultaneously, define `NO_MINUS_C_MINUS_O'. - Macro: AC_PROG_CPP Set output variable `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 (*note 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'. - Macro: AC_PROG_CXX Determine a C++ compiler to use. Check if the environment variable `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). *Note Manual Configuration::, for more on support for cross compiling. - Macro: AC_PROG_CXXCPP Set output variable `CXXCPP' to a command that runs the C++ preprocessor. If `$CXX -E' doesn't work, it uses `/lib/cpp'. It is only portable to run `CXXCPP' on files with a `.c', `.C', or `.cc' extension. If the current language is C++ (*note Language Choice::.), many of the specific test macros use the value of `CXXCPP' indirectly by calling `AC_TRY_CPP', `AC_CHECK_HEADER', `AC_EGREP_HEADER', or `AC_EGREP_CPP'. - Macro: AC_PROG_F77 Determine a Fortran 77 compiler to use. If `F77' is not already set in the environment, check for `g77', `f77' and `f2c', in that order. Set the output variable `F77' to the name of the compiler found. If using `g77' (the GNU Fortran 77 compiler), then `AC_PROG_F77' will set the shell variable `G77' to `yes', and empty otherwise. If the output variable `FFLAGS' was not already set in the environment, then set it to `-g -02' for `g77' (or `-O2' where `g77' does not accept `-g'). Otherwise, set `FFLAGS' to `-g' for all other Fortran 77 compilers. - Macro: AC_PROG_F77_C_O Test if the Fortran 77 compiler accepts the options `-c' and `-o' simultaneously, and define `F77_NO_MINUS_C_MINUS_O' if it does not. - Macro: AC_PROG_GCC_TRADITIONAL Add `-traditional' to output variable `CC' if using the GNU C compiler and `ioctl' does not work properly without `-traditional'. That usually happens when the fixed header files have not been installed on an old system. Since recent versions of the GNU C compiler fix the header files automatically when installed, this is becoming a less prevalent problem. - Macro: AC_PROG_INSTALL Set output variable `INSTALL' to the path of a BSD compatible `install' program, if one is found in the current `PATH'. Otherwise, set `INSTALL' to `DIR/install-sh -c', checking the directories specified to `AC_CONFIG_AUX_DIR' (or its default directories) to determine DIR (*note Output::.). Also set the variables `INSTALL_PROGRAM' and `INSTALL_SCRIPT' to `${INSTALL}' and `INSTALL_DATA' to `${INSTALL} -m 644'. This macro screens out various instances of `install' known to not work. It prefers to find a C program rather than a shell script, for speed. Instead of `install-sh', it can also use `install.sh', but that name is obsolete because some `make' programs have a rule that creates `install' from it if there is no `Makefile'. A copy of `install-sh' which you may use comes with Autoconf. If you use `AC_PROG_INSTALL', you must include either `install-sh' or `install.sh' in your distribution, or `configure' will produce an error message saying it can't find them--even if the system you're on has a good `install' program. This check is a safety measure to prevent you from accidentally leaving that file out, which would prevent your package from installing on systems that don't have a BSD-compatible `install' program. If you need to use your own installation program because it has features not found in standard `install' programs, there is no reason to use `AC_PROG_INSTALL'; just put the pathname of your program into your `Makefile.in' files. - Macro: AC_PROG_LEX If `flex' is found, set output variable `LEX' to `flex' and `LEXLIB' to `-lfl', if that library is in a standard place. Otherwise set `LEX' to `lex' and `LEXLIB' to `-ll'. - Macro: AC_PROG_LN_S If `ln -s' works on the current filesystem (the operating system and filesystem support symbolic links), set output variable `LN_S' to `ln -s', otherwise set it to `ln'. If the link is put in a directory other than the current directory, its meaning depends on whether `ln' or `ln -s' is used. To safely create links using `$(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) - Macro: AC_PROG_RANLIB Set output variable `RANLIB' to `ranlib' if `ranlib' is found, otherwise to `:' (do nothing). - Macro: AC_PROG_YACC If `bison' is found, set output variable `YACC' to `bison -y'. Otherwise, if `byacc' is found, set `YACC' to `byacc'. Otherwise set `YACC' to `yacc'. Generic Program and File Checks ------------------------------- 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 (*note 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) - Macro: AC_CHECK_FILE (FILE [, ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]]) Check whether file FILE exists on the native system. If it is found, execute ACTION-IF-FOUND, otherwise do ACTION-IF-NOT-FOUND, if given. - Macro: AC_CHECK_FILES (FILES[, ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]]) Executes `AC_CHECK_FILE' once for each file listed in FILES. Additionally, defines `HAVEFILE' for each file found, set to 1. - Macro: AC_CHECK_PROG (VARIABLE, PROG-TO-CHECK-FOR, VALUE-IF-FOUND [, VALUE-IF-NOT-FOUND [, PATH, [ REJECT ]]]) Check whether program PROG-TO-CHECK-FOR exists in `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. - Macro: AC_CHECK_PROGS (VARIABLE, PROGS-TO-CHECK-FOR [, VALUE-IF-NOT-FOUND [, PATH]]) Check for each program in the whitespace-separated list PROGS-TO-CHECK-FOR exists in `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. - Macro: AC_CHECK_TOOL (VARIABLE, PROG-TO-CHECK-FOR [, VALUE-IF-NOT-FOUND [, PATH]]) Like `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 (*note Canonicalizing::.). 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. - Macro: AC_PATH_PROG (VARIABLE, PROG-TO-CHECK-FOR [, VALUE-IF-NOT-FOUND [, PATH]]) Like `AC_CHECK_PROG', but set VARIABLE to the entire path of PROG-TO-CHECK-FOR if found. - Macro: AC_PATH_PROGS (VARIABLE, PROGS-TO-CHECK-FOR [, VALUE-IF-NOT-FOUND [, PATH]]) Like `AC_CHECK_PROGS', but if any of PROGS-TO-CHECK-FOR are found, set VARIABLE to the entire path of the program found. Library Files ============= The following macros check for the presence of certain C, C++ or Fortran 77 library archive files. - Macro: AC_CHECK_LIB (LIBRARY, FUNCTION [, ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND [, OTHER-LIBRARIES]]]) Depending on the current language(*note Language Choice::.), try to ensure that the C, C++ or Fortran 77 function FUNCTION is available by checking whether a test program can be linked with the library LIBRARY to get the function. LIBRARY is the base name of the library; e.g., to check for `-lmp', use `mp' as the LIBRARY argument. 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. - Macro: AC_HAVE_LIBRARY (LIBRARY, [, ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND [, OTHER-LIBRARIES]]]) This macro is equivalent to calling `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. - Macro: AC_SEARCH_LIBS (FUNCTION, SEARCH-LIBS [, ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND [, OTHER-LIBRARIES]]]) Search for a library defining FUNCTION, if it's not already available. This equates to calling `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. - Macro: AC_SEARCH_LIBS (FUNCTION, SEARCH-LIBS[, ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]]) This macro is equivalent to calling `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. Library Functions ================= 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. Particular Function Checks -------------------------- These macros check for particular C functions--whether they exist, and in some cases how they respond when given certain arguments. - Macro: AC_FUNC_ALLOCA Check how to get `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 # else # ifdef _AIX #pragma alloca # else # ifndef alloca /* predefined by HP cc +Olibcalls */ char *alloca (); # endif # endif # endif #endif - Macro: AC_FUNC_CLOSEDIR_VOID If the `closedir' function does not return a meaningful value, define `CLOSEDIR_VOID'. Otherwise, callers ought to check its return value for an error indicator. - Macro: AC_FUNC_FNMATCH If the `fnmatch' function is available and works (unlike the one on SunOS 5.4), define `HAVE_FNMATCH'. - Macro: AC_FUNC_GETLOADAVG Check how to get the system load averages. If the system has the `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: 1. It defines `SVR4', `DGUX', `UMAX', or `UMAX4_3' if on those systems. 2. If it finds `nlist.h', it defines `NLIST_STRUCT'. 3. If `struct nlist' has an `n_un' member, it defines `NLIST_NAME_UNION'. 4. If compiling `getloadavg.c' defines `LDAV_PRIVILEGED', programs need to be installed specially on this system for `getloadavg' to work, and this macro defines `GETLOADAVG_PRIVILEGED'. 5. This macro sets the output variable `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. - Macro: AC_FUNC_GETMNTENT Check for `getmntent' in the `sun', `seq', and `gen' libraries, for Irix 4, PTX, and Unixware, respectively. Then, if `getmntent' is available, define `HAVE_GETMNTENT'. - Macro: AC_FUNC_GETPGRP If `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'. - Macro: AC_FUNC_MEMCMP If the `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'. - Macro: AC_FUNC_MMAP If the `mmap' function exists and works correctly, define `HAVE_MMAP'. Only checks private fixed mapping of already-mapped memory. - Macro: AC_FUNC_SELECT_ARGTYPES Determines the correct type to be passed to each of the `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 *'. - Macro: AC_FUNC_SETPGRP If `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'. - Macro: AC_FUNC_SETVBUF_REVERSED If `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. - Macro: AC_FUNC_STRCOLL If the `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. - Macro: AC_FUNC_STRFTIME Check for `strftime' in the `intl' library, for SCO UNIX. Then, if `strftime' is available, define `HAVE_STRFTIME'. - Macro: AC_FUNC_UTIME_NULL If `utime(FILE, NULL)' sets FILE's timestamp to the present, define `HAVE_UTIME_NULL'. - Macro: AC_FUNC_VFORK If `vfork.h' is found, define `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. - Macro: AC_FUNC_VPRINTF If `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.) - Macro: AC_FUNC_WAIT3 If `wait3' is found and fills in the contents of its third argument (a `struct rusage *'), which HP-UX does not do, define `HAVE_WAIT3'. Generic Function Checks ----------------------- 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 (*note Writing Tests::.). - Macro: AC_CHECK_FUNC (FUNCTION, [ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]]) If C function FUNCTION is available, run shell commands ACTION-IF-FOUND, otherwise ACTION-IF-NOT-FOUND. If you just want to define a symbol if the function is available, consider using `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. (*note Language Choice::., for more information about selecting the language for checks.) - Macro: AC_CHECK_FUNCS (FUNCTION... [, ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]]) For each given FUNCTION in the whitespace-separated argument list that is available, define `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. - Macro: AC_REPLACE_FUNCS (FUNCTION...) Like calling `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. Header Files ============ 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. Particular Header Checks ------------------------ These macros check for particular system header files--whether they exist, and in some cases whether they declare certain symbols. - Macro: AC_DECL_SYS_SIGLIST Define `SYS_SIGLIST_DECLARED' if the variable `sys_siglist' is declared in a system header file, either `signal.h' or `unistd.h'. - Macro: AC_DIR_HEADER Like calling `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.h' `DIRENT' `sys/ndir.h' `SYSNDIR' `sys/dir.h' `SYSDIR' `ndir.h' `NDIR' In addition, if the `closedir' function does not return a meaningful value, define `VOID_CLOSEDIR'. - Macro: AC_HEADER_DIRENT Check for the following header files, and for the first one that is found and defines `DIR', define the listed C preprocessor macro: `dirent.h' `HAVE_DIRENT_H' `sys/ndir.h' `HAVE_SYS_NDIR_H' `sys/dir.h' `HAVE_SYS_DIR_H' `ndir.h' `HAVE_NDIR_H' The directory library declarations in the source code should look something like the following: #if HAVE_DIRENT_H # include # define NAMLEN(dirent) strlen((dirent)->d_name) #else # define dirent direct # define NAMLEN(dirent) (dirent)->d_namlen # if HAVE_SYS_NDIR_H # include # endif # if HAVE_SYS_DIR_H # include # endif # if HAVE_NDIR_H # include # 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. - Macro: AC_HEADER_MAJOR If `sys/types.h' does not define `major', `minor', and `makedev', but `sys/mkdev.h' does, define `MAJOR_IN_MKDEV'; otherwise, if `sys/sysmacros.h' does, define `MAJOR_IN_SYSMACROS'. - Macro: AC_HEADER_STDC Define `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 #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)'. - Macro: AC_HEADER_SYS_WAIT If `sys/wait.h' exists and is compatible with POSIX.1, define `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 #if HAVE_SYS_WAIT_H # include #endif #ifndef WEXITSTATUS # define WEXITSTATUS(stat_val) ((unsigned)(stat_val) >> 8) #endif #ifndef WIFEXITED # define WIFEXITED(stat_val) (((stat_val) & 255) == 0) #endif - Macro: AC_MEMORY_H Define `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'. - Macro: AC_UNISTD_H Define `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 # include #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'. - Macro: AC_USG Define `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'. Generic Header Checks --------------------- 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 (*note Writing Tests::.). - Macro: AC_CHECK_HEADER (HEADER-FILE, [ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]]) If the system header file HEADER-FILE exists, execute shell commands ACTION-IF-FOUND, otherwise execute ACTION-IF-NOT-FOUND. If you just want to define a symbol if the header file is available, consider using `AC_CHECK_HEADERS' instead. - Macro: AC_CHECK_HEADERS (HEADER-FILE... [, ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]]) For each given system header file HEADER-FILE in the whitespace-separated argument list that exists, define `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. Structures ========== The following macros check for certain structures or structure members. To check structures not listed here, use `AC_EGREP_CPP' (*note Examining Declarations::.) or `AC_TRY_COMPILE' (*note Examining Syntax::.). - Macro: AC_HEADER_STAT If the macros `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. - Macro: AC_HEADER_TIME If a program may include both `time.h' and `sys/time.h', define `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 # include #else # if HAVE_SYS_TIME_H # include # else # include # endif #endif - Macro: AC_STRUCT_ST_BLKSIZE If `struct stat' contains an `st_blksize' member, define `HAVE_ST_BLKSIZE'. - Macro: AC_STRUCT_ST_BLOCKS If `struct stat' contains an `st_blocks' member, define `HAVE_ST_BLOCKS'. Otherwise, add `fileblocks.o' to the output variable `LIBOBJS'. - Macro: AC_STRUCT_ST_RDEV If `struct stat' contains an `st_rdev' member, define `HAVE_ST_RDEV'. - Macro: AC_STRUCT_TM If `time.h' does not define `struct tm', define `TM_IN_SYS_TIME', which means that including `sys/time.h' had better define `struct tm'. - Macro: AC_STRUCT_TIMEZONE Figure out how to get the current timezone. If `struct tm' has a `tm_zone' member, define `HAVE_TM_ZONE'. Otherwise, if the external array `tzname' is found, define `HAVE_TZNAME'. Typedefs ======== 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. Particular Typedef Checks ------------------------- These macros check for particular C typedefs in `sys/types.h' and `stdlib.h' (if it exists). - Macro: AC_TYPE_GETGROUPS Define `GETGROUPS_T' to be whichever of `gid_t' or `int' is the base type of the array argument to `getgroups'. - Macro: AC_TYPE_MODE_T If `mode_t' is not defined, define `mode_t' to be `int'. - Macro: AC_TYPE_OFF_T If `off_t' is not defined, define `off_t' to be `long'. - Macro: AC_TYPE_PID_T If `pid_t' is not defined, define `pid_t' to be `int'. - Macro: AC_TYPE_SIGNAL If `signal.h' declares `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 () { ... } - Macro: AC_TYPE_SIZE_T If `size_t' is not defined, define `size_t' to be `unsigned'. - Macro: AC_TYPE_UID_T If `uid_t' is not defined, define `uid_t' to be `int' and `gid_t' to be `int'. Generic Typedef Checks ---------------------- This macro is used to check for typedefs not covered by the particular test macros. - Macro: AC_CHECK_TYPE (TYPE, DEFAULT) If the type TYPE is not defined in `sys/types.h', or `stdlib.h' or `stddef.h' if they exist, define it to be the C (or C++) builtin type DEFAULT; e.g., `short' or `unsigned'. C Compiler Characteristics ========================== The following macros check for C compiler or machine architecture features. To check for characteristics not listed here, use `AC_TRY_COMPILE' (*note Examining Syntax::.) or `AC_TRY_RUN' (*note Run Time::.) - Macro: AC_C_BIGENDIAN If words are stored with the most significant byte first (like Motorola and SPARC, but not Intel and VAX, CPUs), define `WORDS_BIGENDIAN'. - Macro: AC_C_CONST If the C compiler does not fully support the keyword `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. - Macro: AC_C_INLINE If the C compiler supports the keyword `inline', do nothing. Otherwise define `inline' to `__inline__' or `__inline' if it accepts one of those, otherwise define `inline' to be empty. - Macro: AC_C_CHAR_UNSIGNED If the C type `char' is unsigned, define `__CHAR_UNSIGNED__', unless the C compiler predefines it. - Macro: AC_C_LONG_DOUBLE If the C compiler supports the `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'. - Macro: AC_C_STRINGIZE If the C preprocessor supports the stringizing operator, define `HAVE_STRINGIZE'. The stringizing operator is `#' and is found in macros such as this: #define x(y) #y - Macro: AC_CHECK_SIZEOF (TYPE [, CROSS-SIZE]) Define `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. - Macro: AC_INT_16_BITS If the C type `int' is 16 bits wide, define `INT_16_BITS'. This macro is obsolete; it is more general to use `AC_CHECK_SIZEOF(int)' instead. - Macro: AC_LONG_64_BITS If the C type `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. Fortran 77 Compiler Characteristics =================================== The following macros check for Fortran 77 compiler characteristics. To check for characteristics not listed here, use `AC_TRY_COMPILE' (*note Examining Syntax::.) or `AC_TRY_RUN' (*note Run Time::.), making sure to first set the current lanuage to Fortran 77 `AC_LANG_FORTRAN77' (*note Language Choice::.). - Macro: AC_F77_LIBRARY_LDFLAGS Determine the linker flags (e.g. `-L' and `-l') for the "Fortran 77 intrinsic and run-time libraries" that are required to successfully link a Fortran 77 program or shared library. The output variable `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 (*note Mixing Fortran 77 With C and C++: (automake)Mixing Fortran 77 With C and C++.). 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. System Services =============== The following macros check for operating system services or capabilities. - Macro: AC_CYGWIN Checks for the Cygwin environment. If present, sets shell variable `CYGWIN' to `yes'. If not present, sets `CYGWIN' to the empty string. - Macro: AC_EXEEXT Defines substitute variable `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. - Macro: AC_OBJEXT Defines substitute variable `OBJEXT' based on the output of the compiler, after .c files have been excluded. Typically set to `.o' if Unix, `.obj' if Win32. - Macro: AC_MINGW32 Checks for the MingW32 compiler environment. If present, sets shell variable `MINGW32' to `yes'. If not present, sets `MINGW32' to the empty string. - Macro: AC_PATH_X Try to locate the X Window System include files and libraries. If the user gave the command line options `--x-includes=DIR' and `--x-libraries=DIR', use those directories. If either or both were not given, get the missing values by running `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. - Macro: AC_PATH_XTRA An enhanced version of `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'. - Macro: AC_SYS_INTERPRETER Check whether the system supports starting scripts with a line of the form `#! /bin/csh' to select the interpreter to use for the script. After running this macro, shell code in `configure.in' can check the shell variable `interpval'; it will be set to `yes' if the system supports `#!', `no' if not. - Macro: AC_SYS_LONG_FILE_NAMES If the system supports file names longer than 14 characters, define `HAVE_LONG_FILE_NAMES'. - Macro: AC_SYS_RESTARTABLE_SYSCALLS If the system automatically restarts a system call that is interrupted by a signal, define `HAVE_RESTARTABLE_SYSCALLS'. UNIX Variants ============= 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. - Macro: AC_AIX If on AIX, define `_ALL_SOURCE'. Allows the use of some BSD functions. Should be called before any macros that run the C compiler. - Macro: AC_DYNIX_SEQ If on Dynix/PTX (Sequent UNIX), add `-lseq' to output variable `LIBS'. This macro is obsolete; instead, use `AC_FUNC_GETMNTENT'. - Macro: AC_IRIX_SUN If on IRIX (Silicon Graphics UNIX), add `-lsun' to output variable `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)'. - Macro: AC_ISC_POSIX If on a POSIXized ISC UNIX, define `_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. - Macro: AC_MINIX If on Minix, define `_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. - Macro: AC_SCO_INTL If on SCO UNIX, add `-lintl' to output variable `LIBS'. This macro is obsolete; instead, use `AC_FUNC_STRFTIME'. - Macro: AC_XENIX_DIR If on Xenix, add `-lx' to output variable `LIBS'. Also, if `dirent.h' is being used, add `-ldir' to `LIBS'. This macro is obsolete; use `AC_HEADER_DIRENT' instead. Writing Tests ************* 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 (*note 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. *Note Writing Macros::, for how to do that. Examining Declarations ====================== 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. - Macro: AC_TRY_CPP (INCLUDES, [ACTION-IF-TRUE [, ACTION-IF-FALSE]]) INCLUDES is C or C++ `#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. - Macro: AC_EGREP_HEADER (PATTERN, HEADER-FILE, ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]) If the output of running the preprocessor on the system header file HEADER-FILE matches the `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) - Macro: AC_EGREP_CPP (PATTERN, PROGRAM, [ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]]) PROGRAM is the text of a C or C++ program, on which shell variable, backquote, and backslash substitutions are performed. If the output of running the preprocessor on PROGRAM matches the `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, *note Language Choice::.), if it hasn't been called already. Examining Syntax ================ 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. - Macro: AC_TRY_COMPILE (INCLUDES, FUNCTION-BODY, [ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]]) Create a C, C++ or Fortran 77 test program (depending on which language is current, *note Language Choice::.), to see whether a function whose body consists of FUNCTION-BODY can be compiled. 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 (*note Examining Libraries::.). 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 (*note Libraries::.), by adding the library being checked for to `LIBS' temporarily and trying to link a small program. - Macro: AC_TRY_LINK (INCLUDES, FUNCTION-BODY, [ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]]) Depending on the current language (*note Language Choice::.), create a test program to see whether a function whose body consists of FUNCTION-BODY can be compiled and linked. 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. - Macro: AC_TRY_LINK_FUNC (FUNCTION, [ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]]) Depending on the current language (*note Language Choice::.), create a test program to see whether a program whose body consists of a prototype of and a call to FUNCTION can be compiled and linked. If the file compiles and links successfully, run shell commands ACTION-IF-FOUND, otherwise run ACTION-IF-NOT-FOUND. - Macro: AC_TRY_LINK_FUNC (FUNCTION, [ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]]) Attempt to compile and link a small program that links with FUNCTION. If the file compiles and links successfully, run shell commands ACTION-IF-FOUND, otherwise run ACTION-IF-NOT-FOUND. - Macro: AC_COMPILE_CHECK (ECHO-TEXT, INCLUDES, FUNCTION-BODY, ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]) This is an obsolete version of `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 (*note Printing Messages::.). Checking Run Time Behavior ========================== 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. Running Test Programs --------------------- Use the following macro if you need to test run-time behavior of the system while configuring. - Macro: AC_TRY_RUN (PROGRAM, [ACTION-IF-TRUE [, ACTION-IF-FALSE [, ACTION-IF-CROSS-COMPILING]]]) PROGRAM is the text of a C program, on which shell variable and backquote substitutions are performed. If it compiles and links successfully and returns an exit status of 0 when executed, run shell commands ACTION-IF-TRUE. Otherwise run shell commands ACTION-IF-FALSE; the exit status of the program is available in the shell variable `$?'. This macro uses `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 (*note Manual Configuration::.). Alternatively, set up a test results cache file with the correct values for the target system (*note 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. - Macro: AC_C_CROSS This macro is obsolete; it does nothing. Guidelines for Test Programs ---------------------------- 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 #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. Test Functions -------------- 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'). Portable Shell Programming ========================== 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. *Note Utilities in Makefiles: (standards)Utilities in Makefiles, 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. Testing Values and Files ======================== `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} Multiple Cases ============== 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 #include ], AC_DEFINE(FSTYPE_STATVFS) fstype=SVR4) if test $fstype = no; then AC_TRY_CPP([#include #include ], AC_DEFINE(FSTYPE_USG_STATFS) fstype=SVR3) fi if test $fstype = no; then AC_TRY_CPP([#include #include ], AC_DEFINE(FSTYPE_AIX_STATFS) fstype=AIX) fi # (more cases omitted here) AC_MSG_RESULT($fstype) Language Choice =============== 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'. - Macro: AC_LANG_C Do compilation tests using `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. - Macro: AC_LANG_CPLUSPLUS Do compilation tests using `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. - Macro: AC_LANG_FORTRAN77 Do compilation tests using `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. - Macro: AC_LANG_SAVE Remember the current language (as set by `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. - Macro: AC_LANG_RESTORE Select the language that is saved on the top of the stack, as set by `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'. - Macro: AC_REQUIRE_CPP Ensure that whichever preprocessor would currently be used for tests has been found. Calls `AC_REQUIRE' (*note Prerequisite Macros::.) with an argument of either `AC_PROG_CPP' or `AC_PROG_CXXCPP', depending on which language is current. Results of Tests **************** 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. Defining C Preprocessor Symbols =============================== 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 "$ac_cv_func_vprintf" != yes; then AC_CHECK_FUNC(_doprnt, AC_DEFINE(HAVE_DOPRNT)) fi If `AC_CONFIG_HEADER' has been called, then instead of creating `DEFS', `AC_OUTPUT' creates a header file by substituting the correct values into `#define' statements in a template file. *Note Configuration Headers::, for more information about this kind of output. - Macro: AC_DEFINE (VARIABLE [, VALUE [, DESCRIPTION]]) Define C preprocessor variable VARIABLE. If VALUE is given, set VARIABLE to that value (verbatim), otherwise set it to 1. VALUE should not contain literal newlines, and if you are not using `AC_CONFIG_HEADER' it should not contain any `#' characters, as `make' tends to eat them. To use a shell variable (which you need to do in order to define a value containing the `m4' quote characters `[' or `]'), use `AC_DEFINE_UNQUOTED' instead. DESCRIPTION is only useful if you are using `AC_CONFIG_HEADER'. In this case, DESCRIPTION is put into the generated `config.h.in' as the comment before the macro define; the macro need not be mentioned in `acconfig.h'. The following example defines the C preprocessor variable `EQUATION' to be the string constant `"$a > $b"': AC_DEFINE(EQUATION, "$a > $b") - Macro: AC_DEFINE_UNQUOTED (VARIABLE [, VALUE [, DESCRIPTION]]) Like `AC_DEFINE', but three shell expansions are performed--once--on VARIABLE and VALUE: variable expansion (`$'), 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="$LIBS -lelf") Setting Output Variables ======================== One way to record the results of tests is to set "output variables", which are shell variables whose values are substituted into files that `configure' outputs. The two macros below create new output variables. *Note Preset Output Variables::, for a list of output variables that are always available. - Macro: AC_SUBST (VARIABLE) Create an output variable from a shell variable. Make `AC_OUTPUT' substitute the variable VARIABLE into output files (typically one or more `Makefile's). This means that `AC_OUTPUT' will replace instances of `@VARIABLE@' in input files with the value that the shell variable VARIABLE has when `AC_OUTPUT' is called. The value of VARIABLE should not contain literal newlines. - Macro: AC_SUBST_FILE (VARIABLE) Another way to create an output variable from a shell variable. Make `AC_OUTPUT' insert (without substitutions) the contents of the file named by shell variable VARIABLE into output files. This means that `AC_OUTPUT' will replace instances of `@VARIABLE@' in output files (such as `Makefile.in') with the contents of the file that the shell variable VARIABLE names when `AC_OUTPUT' is called. Set the variable to `/dev/null' for cases that do not have a file to insert. This macro is useful for inserting `Makefile' fragments containing special dependencies or other `make' directives for particular host or target types into `Makefile's. For example, `configure.in' could contain: AC_SUBST_FILE(host_frag)dnl host_frag=$srcdir/conf/sun4.mh and then a `Makefile.in' could contain: @host_frag@ Caching Results =============== 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. - Macro: AC_CACHE_VAL (CACHE-ID, COMMANDS-TO-SET-IT) Ensure that the results of the check identified by CACHE-ID are available. If the results of the check were in the cache file that was read, and `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. *Note Cache Variable Names::, for how to choose the name of the CACHE-ID variable. - Macro: AC_CACHE_CHECK (MESSAGE, CACHE-ID, COMMANDS) A wrapper for `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. - Macro: AC_CACHE_LOAD Loads values from existing cache file, or creates a new cache file if a cache file is not found. Called automatically from `AC_INIT'. - Macro: AC_CACHE_SAVE Flushes all cached values to the cache file. Called automatically from `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. Cache Variable Names -------------------- 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: PACKAGE-PREFIX An abbreviation for your package or organization; the same prefix you begin local Autoconf macros with, except lowercase by convention. For cache values used by the distributed Autoconf macros, this value is `ac'. `_cv_' Indicates that this shell variable is a cache value. VALUE-TYPE A convention for classifying cache values, to produce a rational naming system. The values used in Autoconf are listed in *Note Macro Names::. SPECIFIC-VALUE Which member of the class of cache values this test applies to. For example, which function (`alloca'), program (`gcc'), or output variable (`INSTALL'). ADDITIONAL-OPTIONS Any particular behavior of the specific member that this test applies to. For example, `broken' or `set'. This part of the name may be omitted if it does not apply. 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. Cache Files ----------- 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. *Note 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 (*note 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 (*note 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) Printing Messages ================= `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. - Macro: AC_MSG_CHECKING (FEATURE-DESCRIPTION) Notify the user that `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. - Macro: AC_MSG_RESULT (RESULT-DESCRIPTION) Notify the user of the results of a check. RESULT-DESCRIPTION is almost always the value of the cache variable for the check, typically `yes', `no', or a file name. This macro should follow a call to `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. - Macro: AC_MSG_ERROR (ERROR-DESCRIPTION) Notify the user of an error that prevents `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'. - Macro: AC_MSG_WARN (PROBLEM-DESCRIPTION) Notify the `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'. - Macro: AC_CHECKING (FEATURE-DESCRIPTION) This macro is similar to `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) - Macro: AC_VERBOSE (RESULT-DESCRIPTION) This macro is similar to `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. Writing Macros ************** 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. Macro Definitions ================= 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 (*note 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 (*note 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. *Note How to define new macros: (m4.info)Definitions, for more complete information on writing `m4' macros. Macro Names =========== 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 (*note 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' C language builtin features. `DECL' Declarations of C variables in header files. `FUNC' Functions in libraries. `GROUP' UNIX group owners of files. `HEADER' Header files. `LIB' C libraries. `PATH' The full path names to files, including programs. `PROG' The base names of programs. `STRUCT' Definitions of C structures in header files. `SYS' Operating system features. `TYPE' C builtin or declared types. `VAR' C variables in libraries. 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'. Quoting ======= 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 th