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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 (see section Prerequisite Macros) with an argument of either AC_PROG_CPP or AC_PROG_CXXCPP, depending on which language is current.


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