@chapter Making @code{configure} Scripts
The configuration scripts that Autoconf produces are by convention
-called @code{configure} when they are distributed. When run, they
-create several files:
+called @code{configure}. When run, @code{configure} creates several
+files, replacing configuration parameters in them with values
+appropriate for the system being configured. The files that
+@code{configure} creates are:
@itemize @bullet
@item
@item
a shell script called @file{config.status} that, when run, will recreate
-the current configuration parameter settings
-(@pxref{Invoking config.status}).
+the files listed above (@pxref{Invoking config.status}).
@end itemize
To create a @code{configure} script with Autoconf, you need to write an
| | | | make* -> your
| | | | /package
| | config.status* -> config.h /
-configure.in \ /
-autoheader* -> - - - - - - - - - - -> config.h.in /
-acconfig.h /
+configure.in \ /
+autoheader* -> - - - - - - - - - - -> config.h.in /
+acconfig.h /
+config.h.top /
@end example
@noindent
-Executables are suffixed by @samp{*}, while files appearing twice are
+Executables are suffixed by @samp{*}. Files appearing twice are
linked with lines of @samp{|}.
@menu
@node Invoking autoheader, , Invoking autoconf, Making configure Scripts
@section Invoking @code{autoheader}
-You can use the program @code{autoheader} to create a template file of C
+You can use the @code{autoheader} program to create a template file of C
@samp{#define} statements for @code{configure} to use. By default, the
file that @code{autoheader} creates is called @file{config.h.in}; if
@file{configure.in} invokes @code{AC_CONFIG_HEADER(@var{file})},
@code{#define} and @code{#undef} statements from a file called
@file{acconfig.h}, which comes with and is installed with Autoconf. It
also uses a file called @file{acconfig.h} in the current directory, if
-present; you must create that file to contain entries for symbols that
-you @code{AC_DEFINE}. For symbols that @code{AC_HAVE_HEADERS} or
-@code{AC_HAVE_FUNCS} define, @code{autoheader} generates comments and
-@code{#undef} statements itself rather than copying them from a file,
-since the possible symbols are effectively limitless.
-
-The file that @code{autoheader} creates contains only @code{#define} and
-@code{#undef} statements and their accompanying comments; there is no
-provision in @code{autoheader} for adding other code or comments to the
-file.
+present; you must create that file to contain entries for any additional
+symbols that you @code{AC_DEFINE}. For symbols defined by
+@code{AC_HAVE_HEADERS}, @code{AC_HAVE_FUNCS}, or @code{AC_HAVE_LIBRARY},
+@code{autoheader} generates comments and @code{#undef} statements itself
+rather than copying them from a file, since the possible symbols are
+effectively limitless.
+
+The file that @code{autoheader} creates usually contains only
+@code{#define} and @code{#undef} statements and their accompanying
+comments. However, if a file called @file{@var{file}.top} (typically
+@file{config.h.top}) exists in the current directory, @code{autoheader}
+copies that file to the beginning of its output.
If you give @code{autoheader} an argument, it uses that file instead of
@file{configure.in} and writes the header file to the standard output
The following macros check for the presence or behavior of particular
programs:
+@ignore
@defmac AC_DECLARE_YYTEXT
@maindex DECLARE_YYTEXT
@vindex DECLARE_YYTEXT
This macro currently does not work, due to problems with shell quoting.
@end defmac
+@end ignore
+
+@defmac AC_GCC_TRADITIONAL
+@maindex GCC_TRADITIONAL
+Add @samp{-traditional} to @code{make} variable @code{CC} if using the
+GNU C compiler and @code{ioctl} does not work properly without
+@samp{-traditional}. This macro calls @code{AC_PROG_CC} and
+@code{AC_PROG_CPP} if they haven't been called already.
+@end defmac
@defmac AC_LN_S
@maindex LN_S
simultaneously, define @code{NO_MINUS_C_MINUS_O}.
@end defmac
-@defmac AC_PROG_YACC
-@maindex PROG_YACC
-If @code{bison} is found, set @code{make} variable @code{YACC} to
-@samp{bison -y}. Otherwise, if @code{byacc} is found, set @code{YACC}
-to @samp{byacc}. Otherwise set @code{YACC} to @samp{yacc}.
+@defmac AC_PROG_AWK
+@maindex PROG_AWK
+Check for @code{mawk}, @code{gawk}, @code{nawk}, and @code{awk}, in that
+order, and set @code{make} variable @code{AWK} to the first one that it
+finds.
+@end defmac
+
+@defmac AC_PROG_CC
+@maindex PROG_CC
+If @code{gcc} is found, set @code{make} variable @code{CC} to @samp{gcc},
+and set shell variable @code{GCC} to 1 for use by macros such as
+@code{AC_GCC_TRADITIONAL}.
@end defmac
@defmac AC_PROG_CPP
been called already.
@end defmac
+@defmac AC_PROG_CXX
+@maindex PROG_CXX
+Determine a C++ compiler to use. Check if the environment variable
+@var{CXX} or @var{CCC} (in that order) is set; if so, set @code{make}
+variable @code{CXX} to its value. Otherwise search for a C++ compiler
+under likely names (@code{c++}, @code{g++}, @code{gcc}, and @code{CC}).
+If none of those checks succeed, as a last resort set @code{CXX} to
+@code{gcc}.
+@end defmac
+
@defmac AC_PROG_CXXCPP
@maindex PROG_CXXCPP
Set shell and @code{make} variable @code{CXXCPP} to a command that runs the
@code{AC_PROG_CXX} if it hasn't been called already.
@end defmac
-@defmac AC_PROG_LEX
-@maindex PROG_LEX
-If @code{flex} is found, set @code{make} variable @code{LEX} to
-@samp{flex} and @code{LEXLIB} to @samp{-lfl}, if that library is in a
-standard place. Otherwise set @code{LEX} to @samp{lex} and
-@code{LEXLIB} to @samp{-ll}.
-@end defmac
-
-@defmac AC_PROG_AWK
-@maindex PROG_AWK
-Check for @code{mawk}, @code{gawk}, @code{nawk}, and @code{awk}, in that
-order, and set @code{make} variable @code{AWK} to the first one that it
-finds.
-@end defmac
-
-@defmac AC_PROG_CC
-@maindex PROG_CC
-If @code{gcc} is found, set @code{make} variable @code{CC} to @samp{gcc},
-and set shell variable @code{GCC} to 1 for use by macros such as
-@code{AC_GCC_TRADITIONAL}.
-@end defmac
-
-@defmac AC_PROG_CXX
-@maindex PROG_CXX
-Determine a C++ compiler to use. Check if the environment variable
-@var{CXX} or @var{CCC} (in that order) is set; if so, set @code{make}
-variable @code{CXX} to its value. Otherwise search for a C++ compiler
-under likely names (@code{c++}, @code{g++}, @code{gcc}, and @code{CC}).
-If none of those checks succeed, as a last resort set @code{CXX} to
-@code{gcc}.
-@end defmac
-
-@defmac AC_GCC_TRADITIONAL
-@maindex GCC_TRADITIONAL
-Add @samp{-traditional} to @code{make} variable @code{CC} if using the
-GNU C compiler and @code{ioctl} does not work properly without
-@samp{-traditional}. This macro calls @code{AC_PROG_CC} and
-@code{AC_PROG_CPP} if they haven't been called already.
-@end defmac
-
@defmac AC_PROG_INSTALL
@maindex PROG_INSTALL
Set @code{make} variable @code{INSTALL} to @samp{install -c} if
@file{Makefile.in} files.
@end defmac
+@defmac AC_PROG_LEX
+@maindex PROG_LEX
+If @code{flex} is found, set @code{make} variable @code{LEX} to
+@samp{flex} and @code{LEXLIB} to @samp{-lfl}, if that library is in a
+standard place. Otherwise set @code{LEX} to @samp{lex} and
+@code{LEXLIB} to @samp{-ll}.
+@end defmac
+
@defmac AC_PROG_RANLIB
@maindex PROG_RANLIB
Set @code{make} variable @code{RANLIB} to @samp{ranlib} if @code{ranlib}
is found, otherwise to @samp{:} (do nothing).
@end defmac
+@defmac AC_PROG_YACC
+@maindex PROG_YACC
+If @code{bison} is found, set @code{make} variable @code{YACC} to
+@samp{bison -y}. Otherwise, if @code{byacc} is found, set @code{YACC}
+to @samp{byacc}. Otherwise set @code{YACC} to @samp{yacc}.
+@end defmac
+
@defmac AC_RSH
@maindex RSH
@vindex NO_REMOTE
@defmac AC_HAVE_POUNDBANG (@var{action-if-supported} @r{[}, @var{action-if-unsupported}@r{]})
@maindex HAVE_POUNDBANG
-Print @samp{checking if `#!' works in shell scripts} to the standard
-output. Then check whether the system supports starting shell scripts
-with a line of the form @samp{#!/bin/csh} to select the shell to run
-them with. @var{action-if-supported} is a list of shell commands to run
-if @samp{#!} works; @var{action-if-not-supported} is a list of shell
-commands to run otherwise.
+Check whether the system supports starting shell scripts with a line of
+the form @samp{#!/bin/csh} to select the shell to use. If @samp{#!}
+works, execute shell commands @var{action-if-supported}; if not, execute
+@var{action-if-not-supported}.
@end defmac
@defmac AC_LONG_FILE_NAMES
fact does (@pxref{Invoking configure}, for more information).
@end defmac
-@defmac AC_PREPARE (@var{unique-file-in-source-dir})
-@maindex PREPARE
-Find the source code directory and set up shell variables necessary for
-other Autoconf macros to work. @var{unique-file-in-source-dir} is some
-file that is in the package's source directory; @code{configure} checks
-for this file's existence to make sure that the directory that it is
-told contains the source code in fact does (@pxref{Invoking configure},
-for more information). @code{AC_PREPARE} is the last thing done by
-@code{AC_INIT}. Use @code{AC_PREPARE} instead of @code{AC_INIT} if you
-want to do argument parsing yourself; never use both.
-@end defmac
-
@defmac AC_OUTPUT (@r{[}@var{file}@dots{}@r{] [,}@var{extra-cmds}@r{]})
@maindex OUTPUT
Create output files (typically one or more @file{Makefile}s) and
@file{config.status} to be run after all its other processing.
@end defmac
+@defmac AC_PREPARE (@var{unique-file-in-source-dir})
+@maindex PREPARE
+Find the source code directory and set up shell variables necessary for
+other Autoconf macros to work. @var{unique-file-in-source-dir} is some
+file that is in the package's source directory; @code{configure} checks
+for this file's existence to make sure that the directory that it is
+told contains the source code in fact does (@pxref{Invoking configure},
+for more information). @code{AC_PREPARE} is the last thing done by
+@code{AC_INIT}. Use @code{AC_PREPARE} instead of @code{AC_INIT} if you
+want to do argument parsing yourself; never use both.
+@end defmac
+
@defmac AC_PREREQ (@var{version})
@maindex PREREQ
Ensure that a recent enough version of Autoconf is being used. If the
@defmac AC_PROGRAM_PATH (@var{variable}, @var{prog-to-check-for}, @var{value-if-not-found})
@maindex PROGRAM_PATH
Similar to @code{AC_PROGRAM_CHECK}, but set @var{variable} to the entire path of
-@var{prog-to-check-for} if found. Otherwise, just set @var{variable} to
-the value of @var{value-if-not-found}; no path checking is performed.
+@var{prog-to-check-for} if found. Otherwise, set @var{variable} to
+the value @var{value-if-not-found} and perform no path checking.
Calls @code{AC_SUBST} for @var{variable}.
@end defmac
@defmac AC_PROGRAMS_PATH (@var{variable}, @var{progs-to-check-for} @r{[}, @var{value-if-not-found}@r{]})
@maindex PROGRAMS_PATH
Like @code{AC_PROGRAMS_CHECK}, but if any of @var{progs-to-check-for}
-are found, @var{variable} is set to the entire pathname of the found
-program.
+are found, set @var{variable} to the entire pathname of the program
+found.
@end defmac
@defmac AC_REPLACE_FUNCS (@var{function-name}@dots{})
@defmac AC_SIZEOF_TYPE (@var{type}, @var{size-var})
@maindex SIZEOF_TYPE
Assign to shell variable @var{size-var} the size (in bytes) of the C (or
-C++) type @var{type}, e.g. @samp{int} or @samp{char *}. If @samp{type}
-is unknown to the compiler, assign 0 to @var{size-var}. The caller will
-likely use @code{AC_DEFINE} to define a symbol in the package being
-configured, based on the value of @var{size-var}. For example,
+C++) builtin type @var{type}, e.g. @samp{int} or @samp{char *}. If
+@samp{type} is unknown to the compiler, assign 0 to @var{size-var}. The
+caller will likely use @code{AC_DEFINE} to define a symbol in the
+package being configured, based on the value of @var{size-var}. For
+example,
@example
AC_SIZEOF_TYPE(char *, psize)
On systems that have @file{unistd.h}, @code{configure} will change the
second line to read @samp{#define HAVE_UNISTD_H 1}. On other systems,
-it will leave the line unchanged.
+it will comment that line out (in case the system predefines that symbol).
Due to the syntactical bizarreness of the Bourne shell, do not use
semicolons to separate @code{AC_DEFINE} calls from other macro calls or
Other macros should rarely need to run @code{echo} directly to print
messages for the @code{configure} 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 the callers
-change automatically.
+changes need only be made to the macro definitions, and all of the
+callers change automatically.
@defmac AC_CHECKING (@var{feature-description})
@maindex CHECKING
-Tell the user that @code{configure} is checking for a particular
+Notify the user that @code{configure} is checking for a particular
feature. This macro prints a message that starts with @samp{checking }.
It prints nothing if @code{configure} is run with the @samp{--silent} or
@samp{--quiet} option. The @var{feature-description} should be
@defmac AC_VERBOSE (@var{result-description})
@maindex VERBOSE
-Notify the user of the results of a check. This extra information is
+Notify the user of the results of a check. This information is
only printed if @code{configure} is run with the @samp{--verbose}
option. @var{result-description} should be something like @samp{setting
ADA to $ADA}.
@node Language Choice, Macro Ordering, Printing Messages, General Purpose Macros
@section Language Choice
-Programs that use both C and C++ need to test features of both
-compilers. The following macros determine which language's compiler is
-used in tests that follow in @file{configure.in}.
+Packages that use both C and C++ need to test features of both
+compilers. Autoconf-generated @code{configure} scripts check for C
+features by default. The following macros determine which language's
+compiler is used in tests that follow in @file{configure.in}.
@defmac AC_LANG_C
@maindex LANG_C
@maindex LANG_SAVE
Remember the current language (as set by @code{AC_LANG_C} or
@code{AC_LANG_CPLUSPLUS}) on a stack. Does not change which language is
-current.
+current. Use this macro and @code{AC_LANG_RESTORE} in macros that need
+to temporarily switch to a particular language.
@end defmac
@defmac AC_REQUIRE_CPP
Running @code{configure} takes a minute or two. While it is running, it
prints some messages that tell what it is doing. If you don't want to
-see the messages, run @code{configure} with its standard output
+see any messages, run @code{configure} with its standard output
redirected to @file{/dev/null}; for example, @samp{./configure >/dev/null}.
To compile the package in a different directory from the one containing
@chapter Making @code{configure} Scripts
The configuration scripts that Autoconf produces are by convention
-called @code{configure} when they are distributed. When run, they
-create several files:
+called @code{configure}. When run, @code{configure} creates several
+files, replacing configuration parameters in them with values
+appropriate for the system being configured. The files that
+@code{configure} creates are:
@itemize @bullet
@item
@item
a shell script called @file{config.status} that, when run, will recreate
-the current configuration parameter settings
-(@pxref{Invoking config.status}).
+the files listed above (@pxref{Invoking config.status}).
@end itemize
To create a @code{configure} script with Autoconf, you need to write an
| | | | make* -> your
| | | | /package
| | config.status* -> config.h /
-configure.in \ /
-autoheader* -> - - - - - - - - - - -> config.h.in /
-acconfig.h /
+configure.in \ /
+autoheader* -> - - - - - - - - - - -> config.h.in /
+acconfig.h /
+config.h.top /
@end example
@noindent
-Executables are suffixed by @samp{*}, while files appearing twice are
+Executables are suffixed by @samp{*}. Files appearing twice are
linked with lines of @samp{|}.
@menu
@node Invoking autoheader, , Invoking autoconf, Making configure Scripts
@section Invoking @code{autoheader}
-You can use the program @code{autoheader} to create a template file of C
+You can use the @code{autoheader} program to create a template file of C
@samp{#define} statements for @code{configure} to use. By default, the
file that @code{autoheader} creates is called @file{config.h.in}; if
@file{configure.in} invokes @code{AC_CONFIG_HEADER(@var{file})},
@code{#define} and @code{#undef} statements from a file called
@file{acconfig.h}, which comes with and is installed with Autoconf. It
also uses a file called @file{acconfig.h} in the current directory, if
-present; you must create that file to contain entries for symbols that
-you @code{AC_DEFINE}. For symbols that @code{AC_HAVE_HEADERS} or
-@code{AC_HAVE_FUNCS} define, @code{autoheader} generates comments and
-@code{#undef} statements itself rather than copying them from a file,
-since the possible symbols are effectively limitless.
-
-The file that @code{autoheader} creates contains only @code{#define} and
-@code{#undef} statements and their accompanying comments; there is no
-provision in @code{autoheader} for adding other code or comments to the
-file.
+present; you must create that file to contain entries for any additional
+symbols that you @code{AC_DEFINE}. For symbols defined by
+@code{AC_HAVE_HEADERS}, @code{AC_HAVE_FUNCS}, or @code{AC_HAVE_LIBRARY},
+@code{autoheader} generates comments and @code{#undef} statements itself
+rather than copying them from a file, since the possible symbols are
+effectively limitless.
+
+The file that @code{autoheader} creates usually contains only
+@code{#define} and @code{#undef} statements and their accompanying
+comments. However, if a file called @file{@var{file}.top} (typically
+@file{config.h.top}) exists in the current directory, @code{autoheader}
+copies that file to the beginning of its output.
If you give @code{autoheader} an argument, it uses that file instead of
@file{configure.in} and writes the header file to the standard output
The following macros check for the presence or behavior of particular
programs:
+@ignore
@defmac AC_DECLARE_YYTEXT
@maindex DECLARE_YYTEXT
@vindex DECLARE_YYTEXT
This macro currently does not work, due to problems with shell quoting.
@end defmac
+@end ignore
+
+@defmac AC_GCC_TRADITIONAL
+@maindex GCC_TRADITIONAL
+Add @samp{-traditional} to @code{make} variable @code{CC} if using the
+GNU C compiler and @code{ioctl} does not work properly without
+@samp{-traditional}. This macro calls @code{AC_PROG_CC} and
+@code{AC_PROG_CPP} if they haven't been called already.
+@end defmac
@defmac AC_LN_S
@maindex LN_S
simultaneously, define @code{NO_MINUS_C_MINUS_O}.
@end defmac
-@defmac AC_PROG_YACC
-@maindex PROG_YACC
-If @code{bison} is found, set @code{make} variable @code{YACC} to
-@samp{bison -y}. Otherwise, if @code{byacc} is found, set @code{YACC}
-to @samp{byacc}. Otherwise set @code{YACC} to @samp{yacc}.
+@defmac AC_PROG_AWK
+@maindex PROG_AWK
+Check for @code{mawk}, @code{gawk}, @code{nawk}, and @code{awk}, in that
+order, and set @code{make} variable @code{AWK} to the first one that it
+finds.
+@end defmac
+
+@defmac AC_PROG_CC
+@maindex PROG_CC
+If @code{gcc} is found, set @code{make} variable @code{CC} to @samp{gcc},
+and set shell variable @code{GCC} to 1 for use by macros such as
+@code{AC_GCC_TRADITIONAL}.
@end defmac
@defmac AC_PROG_CPP
been called already.
@end defmac
+@defmac AC_PROG_CXX
+@maindex PROG_CXX
+Determine a C++ compiler to use. Check if the environment variable
+@var{CXX} or @var{CCC} (in that order) is set; if so, set @code{make}
+variable @code{CXX} to its value. Otherwise search for a C++ compiler
+under likely names (@code{c++}, @code{g++}, @code{gcc}, and @code{CC}).
+If none of those checks succeed, as a last resort set @code{CXX} to
+@code{gcc}.
+@end defmac
+
@defmac AC_PROG_CXXCPP
@maindex PROG_CXXCPP
Set shell and @code{make} variable @code{CXXCPP} to a command that runs the
@code{AC_PROG_CXX} if it hasn't been called already.
@end defmac
-@defmac AC_PROG_LEX
-@maindex PROG_LEX
-If @code{flex} is found, set @code{make} variable @code{LEX} to
-@samp{flex} and @code{LEXLIB} to @samp{-lfl}, if that library is in a
-standard place. Otherwise set @code{LEX} to @samp{lex} and
-@code{LEXLIB} to @samp{-ll}.
-@end defmac
-
-@defmac AC_PROG_AWK
-@maindex PROG_AWK
-Check for @code{mawk}, @code{gawk}, @code{nawk}, and @code{awk}, in that
-order, and set @code{make} variable @code{AWK} to the first one that it
-finds.
-@end defmac
-
-@defmac AC_PROG_CC
-@maindex PROG_CC
-If @code{gcc} is found, set @code{make} variable @code{CC} to @samp{gcc},
-and set shell variable @code{GCC} to 1 for use by macros such as
-@code{AC_GCC_TRADITIONAL}.
-@end defmac
-
-@defmac AC_PROG_CXX
-@maindex PROG_CXX
-Determine a C++ compiler to use. Check if the environment variable
-@var{CXX} or @var{CCC} (in that order) is set; if so, set @code{make}
-variable @code{CXX} to its value. Otherwise search for a C++ compiler
-under likely names (@code{c++}, @code{g++}, @code{gcc}, and @code{CC}).
-If none of those checks succeed, as a last resort set @code{CXX} to
-@code{gcc}.
-@end defmac
-
-@defmac AC_GCC_TRADITIONAL
-@maindex GCC_TRADITIONAL
-Add @samp{-traditional} to @code{make} variable @code{CC} if using the
-GNU C compiler and @code{ioctl} does not work properly without
-@samp{-traditional}. This macro calls @code{AC_PROG_CC} and
-@code{AC_PROG_CPP} if they haven't been called already.
-@end defmac
-
@defmac AC_PROG_INSTALL
@maindex PROG_INSTALL
Set @code{make} variable @code{INSTALL} to @samp{install -c} if
@file{Makefile.in} files.
@end defmac
+@defmac AC_PROG_LEX
+@maindex PROG_LEX
+If @code{flex} is found, set @code{make} variable @code{LEX} to
+@samp{flex} and @code{LEXLIB} to @samp{-lfl}, if that library is in a
+standard place. Otherwise set @code{LEX} to @samp{lex} and
+@code{LEXLIB} to @samp{-ll}.
+@end defmac
+
@defmac AC_PROG_RANLIB
@maindex PROG_RANLIB
Set @code{make} variable @code{RANLIB} to @samp{ranlib} if @code{ranlib}
is found, otherwise to @samp{:} (do nothing).
@end defmac
+@defmac AC_PROG_YACC
+@maindex PROG_YACC
+If @code{bison} is found, set @code{make} variable @code{YACC} to
+@samp{bison -y}. Otherwise, if @code{byacc} is found, set @code{YACC}
+to @samp{byacc}. Otherwise set @code{YACC} to @samp{yacc}.
+@end defmac
+
@defmac AC_RSH
@maindex RSH
@vindex NO_REMOTE
@defmac AC_HAVE_POUNDBANG (@var{action-if-supported} @r{[}, @var{action-if-unsupported}@r{]})
@maindex HAVE_POUNDBANG
-Print @samp{checking if `#!' works in shell scripts} to the standard
-output. Then check whether the system supports starting shell scripts
-with a line of the form @samp{#!/bin/csh} to select the shell to run
-them with. @var{action-if-supported} is a list of shell commands to run
-if @samp{#!} works; @var{action-if-not-supported} is a list of shell
-commands to run otherwise.
+Check whether the system supports starting shell scripts with a line of
+the form @samp{#!/bin/csh} to select the shell to use. If @samp{#!}
+works, execute shell commands @var{action-if-supported}; if not, execute
+@var{action-if-not-supported}.
@end defmac
@defmac AC_LONG_FILE_NAMES
fact does (@pxref{Invoking configure}, for more information).
@end defmac
-@defmac AC_PREPARE (@var{unique-file-in-source-dir})
-@maindex PREPARE
-Find the source code directory and set up shell variables necessary for
-other Autoconf macros to work. @var{unique-file-in-source-dir} is some
-file that is in the package's source directory; @code{configure} checks
-for this file's existence to make sure that the directory that it is
-told contains the source code in fact does (@pxref{Invoking configure},
-for more information). @code{AC_PREPARE} is the last thing done by
-@code{AC_INIT}. Use @code{AC_PREPARE} instead of @code{AC_INIT} if you
-want to do argument parsing yourself; never use both.
-@end defmac
-
@defmac AC_OUTPUT (@r{[}@var{file}@dots{}@r{] [,}@var{extra-cmds}@r{]})
@maindex OUTPUT
Create output files (typically one or more @file{Makefile}s) and
@file{config.status} to be run after all its other processing.
@end defmac
+@defmac AC_PREPARE (@var{unique-file-in-source-dir})
+@maindex PREPARE
+Find the source code directory and set up shell variables necessary for
+other Autoconf macros to work. @var{unique-file-in-source-dir} is some
+file that is in the package's source directory; @code{configure} checks
+for this file's existence to make sure that the directory that it is
+told contains the source code in fact does (@pxref{Invoking configure},
+for more information). @code{AC_PREPARE} is the last thing done by
+@code{AC_INIT}. Use @code{AC_PREPARE} instead of @code{AC_INIT} if you
+want to do argument parsing yourself; never use both.
+@end defmac
+
@defmac AC_PREREQ (@var{version})
@maindex PREREQ
Ensure that a recent enough version of Autoconf is being used. If the
@defmac AC_PROGRAM_PATH (@var{variable}, @var{prog-to-check-for}, @var{value-if-not-found})
@maindex PROGRAM_PATH
Similar to @code{AC_PROGRAM_CHECK}, but set @var{variable} to the entire path of
-@var{prog-to-check-for} if found. Otherwise, just set @var{variable} to
-the value of @var{value-if-not-found}; no path checking is performed.
+@var{prog-to-check-for} if found. Otherwise, set @var{variable} to
+the value @var{value-if-not-found} and perform no path checking.
Calls @code{AC_SUBST} for @var{variable}.
@end defmac
@defmac AC_PROGRAMS_PATH (@var{variable}, @var{progs-to-check-for} @r{[}, @var{value-if-not-found}@r{]})
@maindex PROGRAMS_PATH
Like @code{AC_PROGRAMS_CHECK}, but if any of @var{progs-to-check-for}
-are found, @var{variable} is set to the entire pathname of the found
-program.
+are found, set @var{variable} to the entire pathname of the program
+found.
@end defmac
@defmac AC_REPLACE_FUNCS (@var{function-name}@dots{})
@defmac AC_SIZEOF_TYPE (@var{type}, @var{size-var})
@maindex SIZEOF_TYPE
Assign to shell variable @var{size-var} the size (in bytes) of the C (or
-C++) type @var{type}, e.g. @samp{int} or @samp{char *}. If @samp{type}
-is unknown to the compiler, assign 0 to @var{size-var}. The caller will
-likely use @code{AC_DEFINE} to define a symbol in the package being
-configured, based on the value of @var{size-var}. For example,
+C++) builtin type @var{type}, e.g. @samp{int} or @samp{char *}. If
+@samp{type} is unknown to the compiler, assign 0 to @var{size-var}. The
+caller will likely use @code{AC_DEFINE} to define a symbol in the
+package being configured, based on the value of @var{size-var}. For
+example,
@example
AC_SIZEOF_TYPE(char *, psize)
On systems that have @file{unistd.h}, @code{configure} will change the
second line to read @samp{#define HAVE_UNISTD_H 1}. On other systems,
-it will leave the line unchanged.
+it will comment that line out (in case the system predefines that symbol).
Due to the syntactical bizarreness of the Bourne shell, do not use
semicolons to separate @code{AC_DEFINE} calls from other macro calls or
Other macros should rarely need to run @code{echo} directly to print
messages for the @code{configure} 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 the callers
-change automatically.
+changes need only be made to the macro definitions, and all of the
+callers change automatically.
@defmac AC_CHECKING (@var{feature-description})
@maindex CHECKING
-Tell the user that @code{configure} is checking for a particular
+Notify the user that @code{configure} is checking for a particular
feature. This macro prints a message that starts with @samp{checking }.
It prints nothing if @code{configure} is run with the @samp{--silent} or
@samp{--quiet} option. The @var{feature-description} should be
@defmac AC_VERBOSE (@var{result-description})
@maindex VERBOSE
-Notify the user of the results of a check. This extra information is
+Notify the user of the results of a check. This information is
only printed if @code{configure} is run with the @samp{--verbose}
option. @var{result-description} should be something like @samp{setting
ADA to $ADA}.
@node Language Choice, Macro Ordering, Printing Messages, General Purpose Macros
@section Language Choice
-Programs that use both C and C++ need to test features of both
-compilers. The following macros determine which language's compiler is
-used in tests that follow in @file{configure.in}.
+Packages that use both C and C++ need to test features of both
+compilers. Autoconf-generated @code{configure} scripts check for C
+features by default. The following macros determine which language's
+compiler is used in tests that follow in @file{configure.in}.
@defmac AC_LANG_C
@maindex LANG_C
@maindex LANG_SAVE
Remember the current language (as set by @code{AC_LANG_C} or
@code{AC_LANG_CPLUSPLUS}) on a stack. Does not change which language is
-current.
+current. Use this macro and @code{AC_LANG_RESTORE} in macros that need
+to temporarily switch to a particular language.
@end defmac
@defmac AC_REQUIRE_CPP
Running @code{configure} takes a minute or two. While it is running, it
prints some messages that tell what it is doing. If you don't want to
-see the messages, run @code{configure} with its standard output
+see any messages, run @code{configure} with its standard output
redirected to @file{/dev/null}; for example, @samp{./configure >/dev/null}.
To compile the package in a different directory from the one containing
projects / thirdparty / autoconf.git / commitdiff
