autoheaderto Create config.h.in
autoheader program can create a template file of C
‘#define’ statements for
configure to use.
It searches for the first invocation of
configure sources to determine the name of the template.
(If the first call of
AC_CONFIG_HEADERS specifies more than one
input file name,
autoheader uses the first one.)
It is recommended that only one input file is used. If you want to append
a boilerplate code, it is preferable to use
File conf_post.h is not processed during the configuration then,
which make things clearer. Analogically,
AH_TOP can be used to
prepend a boilerplate code.
In order to do its job,
autoheader needs you to document all
of the symbols that you might use. Typically this is done via an
AC_DEFINE_UNQUOTED call whose first argument
is a literal symbol and whose third argument describes the symbol
(see Defining Symbols). Alternatively, you can use
AH_TEMPLATE (see Autoheader Macros), or you can supply a
suitable input file for a subsequent configuration header file.
Symbols defined by Autoconf’s builtin tests are already documented properly;
you need to document only those that you
You might wonder why
autoheader is needed: after all, why
configure need to “patch” a config.h.in to
produce a config.h instead of just creating config.h from
scratch? Well, when everything rocks, the answer is just that we are
wasting our time maintaining
config.h directly is all that is needed. When things go wrong,
however, you’ll be thankful for the existence of
The fact that the symbols are documented is important in order to
check that config.h makes sense. The fact that there is a
well-defined list of symbols that should be defined (or not) is
also important for people who are porting packages to environments where
configure cannot be run: they just have to fill in the
But let’s come back to the point: the invocation of
If you give
autoheader an argument, it uses that file instead
of configure.ac and writes the header file to the standard output
instead of to config.h.in. If you give
argument of -, it reads the standard input instead of
configure.ac and writes the header file to the standard output.
autoheader accepts the following options:
Print a summary of the command line options and exit.
Print the version number of Autoconf and exit.
Report processing steps.
Don’t remove the temporary files.
Remake the template file even if newer than its input files.
Append dir to the include path. Multiple invocations accumulate.
Prepend dir to the include path. Multiple invocations accumulate.
Enable or disable warnings related to each category. See m4_warn, for a comprehensive list of categories. Special values include:
Enable all categories of warnings.
Disable all categories of warnings.
Treat all warnings as errors.
Disable warnings falling into category.
The enviroment variable
WARNINGS may also be set to a
comma-separated list of warning categories to enable or disable.
It is interpreted exactly the same way as the argument of
--warnings, but unknown categories are silently ignored.
The command line takes precedence; for instance, if
is set to
obsolete, but -Wnone is given on the
command line, no warnings will be issued.
Some categories of warnings are on by default. Again, for details see m4_warn.