(autoconf.info.gz) Configuration Headers

(autoconf.info.gz) Makefile Substitutions
(autoconf.info.gz) Configuration Commands
 
 Configuration Header Files
 ==========================
 
    When a package contains more than a few tests that define C
 preprocessor symbols, the command lines to pass `-D' options to the
 compiler can get quite long.  This causes two problems.  One is that
 the `make' output is hard to visually scan for errors.  More seriously,
 the command lines can exceed the length limits of some operating
 systems.  As an alternative to passing `-D' options to the compiler,
 `configure' scripts can create a C header file containing `#define'
 directives.  The `AC_CONFIG_HEADERS' macro selects this kind of output.
 It should be called right after `AC_INIT'.
 
    The package should `#include' the configuration header file before
 any other header files, to prevent inconsistencies in declarations (for
 example, if it redefines `const').  Use `#include <config.h>' instead
 of `#include "config.h"', and pass the C compiler a `-I.' option (or
 `-I..'; whichever directory contains `config.h').  That way, even if
 the source directory is configured itself (perhaps to make a
 distribution), other build directories can also be configured without
 finding the `config.h' from the source directory.
 
  - Macro: AC_CONFIG_HEADERS (HEADER ..., [CMDS], [INIT-CMDS])
      This macro is one of the instantiating macros; see 
      Configuration Actions.  Make `AC_OUTPUT' create the file(s) in
      the whitespace-separated list HEADER containing C preprocessor
      `#define' statements, and replace `@DEFS@' in generated files with
      `-DHAVE_CONFIG_H' instead of the value of `DEFS'.  The usual name
      for HEADER is `config.h'.
 
      If HEADER already exists and its contents are identical to what
      `AC_OUTPUT' would put in it, it is left alone.  Doing this allows
      making some changes in the configuration without needlessly
      causing object files that depend on the header file to be
      recompiled.
 
      Usually the input file is named `HEADER.in'; however, you can
      override the input file name by appending to HEADER a
      colon-separated list of input files.  Examples:
 
           AC_CONFIG_HEADERS([config.h:config.hin])
           AC_CONFIG_HEADERS([defines.h:defs.pre:defines.h.in:defs.post])
 
      Doing this allows you to keep your file names acceptable to
      MS-DOS, or to prepend and/or append boilerplate to the file.
 
     Configuration Actions, for more details on HEADER.
(autoconf.info.gz) Configuration Headers

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