gnulib/doc/configmake.texi

@node configmake
@section configmake

@mindex configmake
@cindex @file{configmake.h}, module for updating

The @code{configmake} module builds a C include file named
@file{configmake.h} containing the usual installation directory
values; for example, those specified by @code{--prefix} or
@code{--libdir} to configure.  Each variable is given a @code{#define}
with an all-uppercase macro name, such as @code{PREFIX} and
@code{LIBDIR}.  (Automake cannot create this file directly because the
user might override directory values at @code{make} time.)

Specifically, the module retrieves values of the variables through
@code{configure} followed by @code{make}, not directly through
@code{configure}, so that a user who sets some of these variables
consistently on the @code{make} command line gets correct results.

One advantage of this approach, compared to the classical approach of
adding @code{-DLIBDIR=\"$(libdir)\"} etc.@: to @code{AM_CPPFLAGS}, is
that it protects against the use of undefined variables.  That is, if,
say, @code{$(libdir)} is not set in the Makefile, @code{LIBDIR} is not
defined by this module, and code using @code{LIBDIR} gives a
compilation error.

Another advantage is that @code{make} output is shorter.

For the complete list of variables which are @code{#define}d this way,
see the file @file{gnulib/modules/configmake}, or inspect your
resulting gnulib Makefile.