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(autoconf.info)Preset Output Variables

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Preset Output Variables
-----------------------

   Some output variables are preset by the Autoconf macros.  Some of the
Autoconf macros set additional output variables, which are mentioned in
the descriptions for those macros.  Note: Output Variable Index, for a
complete list of output variables.  Note: Installation Directory
Variables, for the list of the preset ones related to installation
directories.  Below are listed the other preset ones.  They all are
precious variables (Note: Setting Output Variables, `AC_ARG_VAR').

 - Variable: CFLAGS
     Debugging and optimization options for the C compiler.  If it is
     not set in the environment when `configure' runs, the default
     value is set when you call `AC_PROG_CC' (or empty if you don't).
     `configure' uses this variable when compiling programs to test for
     C features.

 - Variable: configure_input
     A comment saying that the file was generated automatically by
     `configure' and giving the name of the input file.  `AC_OUTPUT'
     adds a comment line containing this variable to the top of every
     `Makefile' it creates.  For other files, you should reference this
     variable in a comment at the top of each input file.  For example,
     an input shell script should begin like this:

          #! /bin/sh
          # @configure_input@

     The presence of that line also reminds people editing the file
     that it needs to be processed by `configure' in order to be used.

 - Variable: CPPFLAGS
     Header file search directory (`-IDIR') and any other miscellaneous
     options for the C and C++ preprocessors and compilers.  If it is
     not set in the environment when `configure' runs, the default
     value is empty.  `configure' uses this variable when compiling or
     preprocessing programs to test for C and C++ features.

 - Variable: CXXFLAGS
     Debugging and optimization options for the C++ compiler.  If it is
     not set in the environment when `configure' runs, the default
     value is set when you call `AC_PROG_CXX' (or empty if you don't).
     `configure' uses this variable when compiling programs to test for
     C++ features.

 - Variable: DEFS
     `-D' options to pass to the C compiler.  If `AC_CONFIG_HEADERS' is
     called, `configure' replaces `@DEFS@' with `-DHAVE_CONFIG_H'
     instead (Note: Configuration Headers).  This variable is not
     defined while `configure' is performing its tests, only when
     creating the output files.  Note: Setting Output Variables, for
     how to check the results of previous tests.

 - Variable: ECHO_C
 - Variable: ECHO_N
 - Variable: ECHO_T
     How does one suppress the trailing newline from `echo' for
     question-answer message pairs?  These variables provide a way:

          echo $ECHO_N "And the winner is... $ECHO_C"
          sleep 100000000000
          echo "${ECHO_T}dead."

     Some old and uncommon `echo' implementations offer no means to
     achieve this, in which case `ECHO_T' is set to tab.  You might not
     want to use it.

 - Variable: FFLAGS
     Debugging and optimization options for the Fortran 77 compiler.
     If it is not set in the environment when `configure' runs, the
     default value is set when you call `AC_PROG_F77' (or empty if you
     don't).  `configure' uses this variable when compiling programs to
     test for Fortran 77 features.

 - Variable: LDFLAGS
     Stripping (`-s'), path (`-L'), and any other miscellaneous options
     for the linker.  Don't use this variable to pass library names
     (`-l') to the linker, use `LIBS' instead.  If it is not set in the
     environment when `configure' runs, the default value is empty.
     `configure' uses this variable when linking programs to test for
     C, C++ and Fortran 77 features.

 - Variable: LIBS
     `-l' options to pass to the linker.  The default value is empty,
     but some Autoconf macros may prepend extra libraries to this
     variable if those libraries are found and provide necessary
     functions, see Note: Libraries.  `configure' uses this variable
     when linking programs to test for C, C++ and Fortran 77 features.

 - Variable: builddir
     Rigorously equal to `.'.  Added for symmetry only.

 - Variable: abs_builddir
     Absolute path of `builddir'.

 - Variable: top_builddir
     The relative path to the top-level of the current build tree.  In
     the top-level directory, this is the same as `srcbuild'.

 - Variable: abs_top_builddir
     Absolute path of `top_builddir'.

 - Variable: srcdir
     The relative path to the directory that contains the source code
     for that `Makefile'.

 - Variable: abs_srcdir
     Absolute path of `srcdir'.

 - Variable: top_srcdir
     The relative path to the top-level source code directory for the
     package.  In the top-level directory, this is the same as `srcdir'.

 - Variable: abs_top_srcdir
     Absolute path of `top_srcdir'.