(autoconf.info)Preset Output Variables


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4.8.1 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 or linking programs
     to test for C features.

     If a compiler option affects only the behavior of the preprocessor
     (e.g., `-D NAME'), it should be put into `CPPFLAGS' instead.  If
     it affects only the linker (e.g., `-L DIRECTORY'), it should be
     put into `LDFLAGS' instead.  If it affects only the compiler
     proper, `CFLAGS' is the natural home for it.  If an option affects
     multiple phases of the compiler, though, matters get tricky.  One
     approach to put such options directly into `CC', e.g., `CC='gcc
     -m64''.  Another is to put them into both `CPPFLAGS' and
     `LDFLAGS', but not into `CFLAGS'.


 -- 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
     Preprocessor options for the C, C++, and Objective 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 preprocessing or compiling programs to test for
     C, C++, and Objective C features.

     This variable's contents should contain options like `-I', `-D',
     and `-U' that affect only the behavior of the preprocessor.
     Please see the explanation of `CFLAGS' for what you can do if an
     option affects other phases of the compiler as well.

     Currently, `configure' always links as part of a single invocation
     of the compiler that also preprocesses and compiles, so it uses
     this variable also when linking programs.  However, it is unwise to
     depend on this behavior because the GNU coding standards do not
     require it and many packages do not use `CPPFLAGS' when linking
     programs.

     Note: Special Chars in Variables, for limitations that `CPPFLAGS'
     might run into.

 -- Variable: CXXFLAGS
     Debugging and optimization options for the C++ compiler.  It acts
     like `CFLAGS', but for C++ instead of C.

 -- 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: ERLCFLAGS
     Debugging and optimization options for the Erlang compiler.  If it
     is not set in the environment when `configure' runs, the default
     value is empty.  `configure' uses this variable when compiling
     programs to test for Erlang features.

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

 -- 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 or linking
     programs to test for Fortran 77 features.

 -- Variable: LDFLAGS
     Options for the linker.  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++, Objective
     C, and Fortran features.

     This variable's contents should contain options like `-s' and `-L'
     that affect only the behavior of the linker.  Please see the
     explanation of `CFLAGS' for what you can do if an option also
     affects other phases of the compiler.

     Don't use this variable to pass library names (`-l') to the
     linker; use `LIBS' instead.

 -- 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 features.

 -- Variable: OBJCFLAGS
     Debugging and optimization options for the Objective C compiler.
     It acts like `CFLAGS', but for Objective C instead of C.

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

 -- Variable: abs_builddir
     Absolute name of `builddir'.

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

 -- Variable: top_build_prefix
     The relative name of the top level of the current build tree with
     final slash if nonemtpy.  This is the same as `top_builddir',
     except that it contains of zero of more runs of `../', so it
     should not be appended with a slash for concatenation.  This helps
     for `make' implementations that otherwise do not treat `./file'
     and `file' as equal in the toplevel build directory.

 -- Variable: abs_top_builddir
     Absolute name of `top_builddir'.

 -- Variable: srcdir
     The name of the directory that contains the source code for that
     makefile.

 -- Variable: abs_srcdir
     Absolute name of `srcdir'.

 -- Variable: top_srcdir
     The name of 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 name of `top_srcdir'.


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