configure.texi

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help identify potential portability problems, and hence configure tests
that you will want to use.
@ifnothtml
@xref{Invoking autoscan, , , autoconf, the autoconf manual}.
@end ifnothtml
@ifhtml
See @uref{http://www.delorie.com/gnu/docs/autoconf/autoconf_4.html, the
autoscan documentation}.
@end ifhtml

Another handy tool for an existing body of code is @samp{ifnames}.  This
will show you all the preprocessor conditionals that the code already
uses.
@ifnothtml
@xref{Invoking ifnames, , , autoconf, the autoconf manual}.
@end ifnothtml
@ifhtml
See @uref{http://www.delorie.com/gnu/docs/autoconf/autoconf_5.html, the
ifnames documentation}.
@end ifhtml

Besides the portability tests which are specific to your particular
package, every @file{configure.in} file should contain the following
macros.

@table @samp
@item AC_INIT
@cindex @samp{AC_INIT}
This macro takes a single argument, which is the name of a file in your
package.  For example, @samp{AC_INIT(foo.c)}.

@item AC_PREREQ(@var{VERSION})
@cindex @samp{AC_PREREQ}
This macro is optional.  It may be used to indicate the version of
@samp{autoconf} that you are using.  This will prevent users from
running an earlier version of @samp{autoconf} and perhaps getting an
invalid @file{configure} script.  For example, @samp{AC_PREREQ(2.12)}.

@item AM_INIT_AUTOMAKE
@cindex @samp{AM_INIT_AUTOMAKE}
This macro takes two arguments: the name of the package, and a version
number.  For example, @samp{AM_INIT_AUTOMAKE(foo, 1.0)}.  (This macro is
not needed if you are not using automake).

@item AM_CONFIG_HEADER
@cindex @samp{AM_CONFIG_HEADER}
This macro names the header file which will hold the preprocessor macro
definitions at run time.  Normally this should be @file{config.h}.  Your
sources would then use @samp{#include "config.h"} to include it.

This macro may optionally name the input file for that header file; by
default, this is @file{config.h.in}, but that file name works poorly on
DOS filesystems.  Therefore, it is often better to name it explicitly as
@file{config.in}.

This is what you should normally put in @file{configure.in}:
@example
AM_CONFIG_HEADER(config.h:config.in)
@end example

@cindex @samp{AC_CONFIG_HEADER}
(If you are not using automake, use @samp{AC_CONFIG_HEADER} rather than
@samp{AM_CONFIG_HEADER}).

@item AM_MAINTAINER_MODE
@cindex @samp{AM_MAINTAINER_MODE}
This macro always appears in Cygnus configure scripts.  Other programs
may or may not use it.

If this macro is used, the @samp{--enable-maintainer-mode} option is
required to enable automatic rebuilding of generated files used by the
configure system.  This of course requires that developers be aware of,
and use, that option.

If this macro is not used, then the generated files will always be
rebuilt automatically.  This will cause problems if the wrong versions
of autoconf, automake, or others are in the builder's @samp{PATH}.

(If you are not using automake, you do not need to use this macro).

@item AC_EXEEXT
@cindex @samp{AC_EXEEXT}
@cindex @samp{AM_EXEEXT}
Either this macro or @samp{AM_EXEEXT} always appears in Cygnus configure
files.  Other programs may or may not use one of them.

This macro looks for the executable suffix used on the host system.  On
Unix systems, this is the empty string.  On Windows systems, this is
@samp{.exe}.  This macro directs automake to use the executable suffix
as appropriate when creating programs.  This macro does not take any
arguments.

The @samp{AC_EXEEXT} form is new, and is part of a Cygnus patch to
autoconf to support compiling with Visual C++.  Older programs use
@samp{AM_EXEEXT} instead.

(Programs which do not use automake use neither @samp{AC_EXEEXT} nor
@samp{AM_EXEEXT}).

@item AC_PROG_CC
@cindex @samp{AC_PROG_CC}
If you are writing C code, you will normally want to use this macro.  It
locates the C compiler to use.  It does not take any arguments.

However, if this @file{configure.in} file is for a library which is to
be compiled by a cross compiler which may not fully work, then you will
not want to use @samp{AC_PROG_CC}.  Instead, you will want to use a
variant which does not call the macro @samp{AC_PROG_CC_WORKS}.  Examples
can be found in various @file{configure.in} files for libraries that are
compiled with cross compilers, such as libiberty or libgloss.  This is
essentially a bug in autoconf, and there will probably be a better
workaround at some point.

@item AC_PROG_CXX
@cindex @samp{AC_PROG_CXX}
If you are writing C++ code, you will want to use this macro.  It
locates the C++ compiler to use.  It does not take any arguments.  The
same cross compiler comments apply as for @samp{AC_PROG_CC}.

@item AM_PROG_LIBTOOL
@cindex @samp{AM_PROG_LIBTOOL}
If you want to build libraries, and you want to permit them to be
shared, or you want to link against libraries which were built using
libtool, then you will need this macro.  This macro is required in order
to use libtool.

@cindex @samp{AM_DISABLE_SHARED}
By default, this will cause all libraries to be built as shared
libraries.  To prevent this--to change the default--use
@samp{AM_DISABLE_SHARED} before @samp{AM_PROG_LIBTOOL}.  The configure
options @samp{--enable-shared} and @samp{--disable-shared} may be used
to override the default at build time.

@item AC_DEFINE(_GNU_SOURCE)
@cindex @samp{_GNU_SOURCE}
GNU packages should normally include this line before any other feature
tests.  This defines the macro @samp{_GNU_SOURCE} when compiling, which
directs the libc header files to provide the standard GNU system
interfaces including all GNU extensions.  If this macro is not defined,
certain GNU extensions may not be available.

@item AC_OUTPUT
@cindex @samp{AC_OUTPUT}
This macro takes a list of file names which the configure process should
produce.  This is normally a list of one or more @file{Makefile} files
in different directories.  If your package lives entirely in a single
directory, you would use simply @samp{AC_OUTPUT(Makefile)}.  If you also
have, for example, a @file{lib} subdirectory, you would use
@samp{AC_OUTPUT(Makefile lib/Makefile)}.
@end table

If you want to use locally defined macros in your @file{configure.in}
file, then you will need to write a @file{acinclude.m4} file which
defines them (if not using automake, this file is called
@file{aclocal.m4}).  Alternatively, you can put separate macros in an
@file{m4} subdirectory, and put @samp{ACLOCAL_AMFLAGS = -I m4} in your
@file{Makefile.am} file so that the @samp{aclocal} program will be able
to find them.

The different macro prefixes indicate which tool defines the macro.
Macros which start with @samp{AC_} are part of autoconf.  Macros which
start with @samp{AM_} are provided by automake or libtool.

@node Write Makefile.am
@section Write Makefile.am
@cindex @file{Makefile.am}, writing

You must write the file @file{Makefile.am}.  This is an automake input
file, and the automake manual describes in detail what this file should
look like.

The automake commands in @file{Makefile.am} mostly look like variable
assignments in a @file{Makefile}.  automake recognizes special variable
names, and automatically add make rules to the output as needed.

There will be one @file{Makefile.am} file for each directory in your
package.  For each directory with subdirectories, the @file{Makefile.am}
file should contain the line
@smallexample
SUBDIRS = @var{dir} @var{dir} @dots{}
@end smallexample
@noindent
where each @var{dir} is the name of a subdirectory.

For each @file{Makefile.am}, there should be a corresponding
@file{Makefile} in the @samp{AC_OUTPUT} macro in @file{configure.in}.

Every @file{Makefile.am} written at Cygnus should contain the line
@smallexample
AUTOMAKE_OPTIONS = cygnus
@end smallexample
@noindent
This puts automake into Cygnus mode.  See the automake manual for
details.

You may to include the version number of @samp{automake} that you are
using on the @samp{AUTOMAKE_OPTIONS} line.  For example,
@smallexample
AUTOMAKE_OPTIONS = cygnus 1.3
@end smallexample
@noindent
This will prevent users from running an earlier version of
@samp{automake} and perhaps getting an invalid @file{Makefile.in}.

If your package builds a program, then in the directory where that
program is built you will normally want a line like
@smallexample
bin_PROGRAMS = @var{program}
@end smallexample
@noindent
where @var{program} is the name of the program.  You will then want a
line like
@smallexample
@var{program}_SOURCES = @var{file} @var{file} @dots{}
@end smallexample
@noindent
where each @var{file} is the name of a source file to link into the
program (e.g., @samp{foo.c}).

If your package builds a library, and you do not want the library to
ever be built as a shared library, then in the directory where that
library is built you will normally want a line like
@smallexample
lib_LIBRARIES = lib@var{name}.a
@end smallexample
@noindent
where @samp{lib@var{name}.a} is the name of the library.  You will then
want a line like
@smallexample
lib@var{name}_a_SOURCES = @var{file} @var{file} @dots{}
@end smallexample
@noindent
where each @var{file} is the name of a source file to add to the
library.

If your package builds a library, and you want to permit building the
library as a shared library, then in the directory where that library is
built you will normally want a line like
@smallexample
lib_LTLIBRARIES = lib@var{name}.la
@end smallexample
The use of @samp{LTLIBRARIES}, and the @samp{.la} extension, indicate a
library to be built using libtool.  As usual, you will then want a line
like
@smallexample
lib@var{name}_la_SOURCES = @var{file} @var{file} @dots{}
@end smallexample

The strings @samp{bin} and @samp{lib} that appear above in
@samp{bin_PROGRAMS} and @samp{lib_LIBRARIES} are not arbitrary.  They
refer to particular directories, which may be set by the @samp{--bindir}
and @samp{--libdir} options to @file{configure}.  If those options are
not used, the default values are based on the @samp{--prefix} or
@samp{--exec-prefix} options to @file{configure}.  It is possible to use
other names if the program or library should be installed in some other
directory.

The @file{Makefile.am} file may also contain almost anything that may
appear in a normal @file{Makefile}.  automake also supports many other
special variables, as well as conditionals.

See the automake manual for more information.

@node Write acconfig.h
@section Write acconfig.h
@cindex @file{acconfig.h}, writing

If you are generating a portability header file, (i.e., you are using
@samp{AM_CONFIG_HEADER} in @file{configure.in}), then you will have to
write a @file{acconfig.h} file.  It will have to contain the following
lines.

@smallexample
/* Name of package.  */
#undef PACKAGE

/* Version of package.  */
#undef VERSION
@end smallexample

This requirement is really a bug in the system, and the requirement may
be eliminated at some later date.

The @file{acconfig.h} file will also similar comment and @samp{#undef}
lines for any unusual macros in the @file{configure.in} file, including
any macro which appears in a @samp{AC_DEFINE} macro.

In particular, if you are writing a GNU package and therefore include
@samp{AC_DEFINE(_GNU_SOURCE)} in @file{configure.in} as suggested above,
you will need lines like this in @file{acconfig.h}:
@smallexample
/* Enable GNU extensions.  */
#undef _GNU_SOURCE
@end smallexample

Normally the @samp{autoheader} program will inform you of any such
requirements by printing an error message when it is run.  However, if
you do anything particular odd in your @file{configure.in} file, you
will have to make sure that the right entries appear in
@file{acconfig.h}, since otherwise the results of the tests may not be
available in the @file{config.h} file which your code will use.

(Thee @samp{PACKAGE} and @samp{VERSION} lines are not required if you
are not using automake, and in that case you may not need a
@file{acconfig.h} file at all).

@node Generate files
@section Generate files

Once you have written @file{configure.in}, @file{Makefile.am},
@file{acconfig.h}, and possibly @file{acinclude.m4}, you must use
autoconf and automake programs to produce the first versions of the
generated files.  This is done by executing the following sequence of
commands.

@smallexample
aclocal
autoconf
autoheader
automake
@end smallexample

The @samp{aclocal} and @samp{automake} commands are part of the automake
package, and the @samp{autoconf} and @samp{autoheader} commands are part
of the autoconf package.

If you are using a @file{m4} subdirectory for your macros, you will need
to use the @samp{-I m4} option when you run @samp{aclocal}.

If you are not using the Cygnus tree, use the @samp{-a} option when
running @samp{automake} command in order to copy the required support
files into your source directory.

If you are using libtool, you must build and install the libtool package
with the same @samp{--prefix} and @samp{--exec-prefix} options as you
used with the autoconf and automake packages.  You must do this before
running any of the above commands.  If you are not using the Cygnus
tree, you will need to run the @samp{libtoolize} program to copy the
libtool support files into your directory.

Once you have managed to run these commands without getting any errors,
you should create a new empty directory, and run the @samp{configure}
script which will have been created by @samp{autoconf} with the
@samp{--enable-maintainer-mode} option.  This will give you a set of
Makefiles which will include rules to automatically rebuild all the
generated files.

After doing that, whenever you have changed some of the input files and
want to regenerated the other files, go to your object directory and run