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(autoconf.info)Language Choice

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Language Choice
===============

   Packages that use both C and C++ need to test features of both
compilers.  Autoconf-generated `configure' scripts check for C features
by default.  The following macros determine which language's compiler
is used in tests that follow in `configure.in'.

 - Macro: AC_LANG_C
     Do compilation tests using `CC' and `CPP' and use extension `.c'
     for test programs.  Set the shell variable `cross_compiling' to
     the value computed by `AC_PROG_CC' if it has been run, empty
     otherwise.

 - Macro: AC_LANG_CPLUSPLUS
     Do compilation tests using `CXX' and `CXXCPP' and use extension
     `.C' for test programs.  Set the shell variable `cross_compiling'
     to the value computed by `AC_PROG_CXX' if it has been run, empty
     otherwise.

 - Macro: AC_LANG_FORTRAN77
     Do compilation tests using `F77' and use extension `.f' for test
     programs.  Set the shell variable `cross_compiling' to the value
     computed by `AC_PROG_F77' if it has been run, empty otherwise.

 - Macro: AC_LANG_SAVE
     Remember the current language (as set by `AC_LANG_C',
     `AC_LANG_CPLUSPLUS' or `AC_LANG_FORTRAN77') on a stack.  Does not
     change which language is current.  Use this macro and
     `AC_LANG_RESTORE' in macros that need to temporarily switch to a
     particular language.

 - Macro: AC_LANG_RESTORE
     Select the language that is saved on the top of the stack, as set
     by `AC_LANG_SAVE', and remove it from the stack.  This macro is
     equivalent to either `AC_LANG_C', `AC_LANG_CPLUSPLUS' or
     `AC_LANG_FORTRAN77', whichever had been run most recently when
     `AC_LANG_SAVE' was last called.

     Do not call this macro more times than `AC_LANG_SAVE'.

 - Macro: AC_REQUIRE_CPP
     Ensure that whichever preprocessor would currently be used for
     tests has been found.  Calls `AC_REQUIRE' (Note: Prerequisite
     Macros) with an argument of either `AC_PROG_CPP' or
     `AC_PROG_CXXCPP', depending on which language is current.