@node ax_define_sub_path
@unnumberedsec ax_define_sub_path

@majorheading Synopsis

@smallexample
AX_DEFINE_SUB_PATH(DEFNAME, varname, description)
@end smallexample

@majorheading Description

Look at varname and detect the subpath that it contains relative to
$prefix/$exec_prefix. If the path is indeed relative to
$prefix/$exec_prefix, then a single "./" (dotslash) is prepended,
otherwise it can be seen as an absolute path that cannot be moved, which
you possibly do for "/etc" files, or even those ending up in
"/lib/modules" or "/winnt/system".

This macro is not very intelligent, it's just a first try in this
direction. It does currently just look into the current patterns, and
replaces a $@{prefix@} with a simple dot. Amazingly, it works quite well
for most packages.

Example (configure.ac):

@smallexample
  AX_DEFINE_DIR([EPREFIX], [exec_prefix], [--exec-prefix or default])
  AX_DEFINE_SUB_PATH([PATH_LIBDIR], [libdir], [--bindir subdir])
  AC_DEFINE_UNQUOTED([PACKAGE],"$PACKAGE", [Name of package])
@end smallexample

Example (in C):

@smallexample
  static const char _libdir[] = PATH_LIBDIR; /* configure default */
  char* libdir;
  char* eprefix = getenv (PACKAGE "DIR");
  if (! eprefix) eprefix = EPREFIX; /* default */
  if (*_libdir != '.') libdir = strdup(_libdir);
  else @{
     libdir = malloc(strlen(eprefix) + strlen(_libdir) + 2);
     strcpy(libdir, eprefix);
     strcat(libdir, PATH_DELIMITER_STRING);
     strcat(libdir, _libdir);
  @}
  ...
  free (libdir);
@end smallexample

The AX_DEFINE_SUB_PATHS(varnames) macro looks for the given various
install-paths that largely depend on either $@{prefix@} or $@{exec_prefix@}.
Just cut out the prefix and ac_define the value. The value is uppercased
and PATH_ prepended ie. ax_define_sub_paths(bindir libdir pkgdatadir)
will create the defines PATH_BINDIR PATH_LIBDIR PATH_PKGDATADIR - see
posix' include/paths.h that creates _PATH_DEV and friends.

@majorheading Source Code

Download the
@uref{http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=blob_plain;f=m4/ax_define_sub_path.m4,latest
version of @file{ax_define_sub_path.m4}} or browse
@uref{http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=history;f=m4/ax_define_sub_path.m4,the
macro's revision history}.

@majorheading License

@w{Copyright @copyright{} 2008 Guido U. Draheim @email{guidod@@gmx.de}}

Copying and distribution of this file, with or without modification, are
permitted in any medium without royalty provided the copyright notice
and this notice are preserved.  This file is offered as-is, without any
warranty.