(autoconf.info)Language Choice


Next: Writing Test Programs Up: Writing Tests

6.1 Language Choice
===================

Autoconf-generated `configure' scripts check for the C compiler and its
features by default.  Packages that use other programming languages
(maybe more than one, e.g., C and C++) need to test features of the
compilers for the respective languages.  The following macros determine
which programming language is used in the subsequent tests in
`configure.ac'.

 -- Macro: AC_LANG (LANGUAGE)
     Do compilation tests using the compiler, preprocessor, and file
     extensions for the specified LANGUAGE.

     Supported languages are:

    `C'
          Do compilation tests using `CC' and `CPP' and use extension
          `.c' for test programs.  Use compilation flags: `CPPFLAGS'
          with `CPP', and both `CPPFLAGS' and `CFLAGS' with `CC'.

    `C++'
          Do compilation tests using `CXX' and `CXXCPP' and use
          extension `.C' for test programs.  Use compilation flags:
          `CPPFLAGS' with `CXXCPP', and both `CPPFLAGS' and `CXXFLAGS'
          with `CXX'.

    `Fortran 77'
          Do compilation tests using `F77' and use extension `.f' for
          test programs.  Use compilation flags: `FFLAGS'.

    `Fortran'
          Do compilation tests using `FC' and use extension `.f' (or
          whatever has been set by `AC_FC_SRCEXT') for test programs.
          Use compilation flags: `FCFLAGS'.

    `Erlang'
          Compile and execute tests using `ERLC' and `ERL' and use
          extension `.erl' for test Erlang modules.  Use compilation
          flags: `ERLCFLAGS'.

    `Objective C'
          Do compilation tests using `OBJC' and `OBJCPP' and use
          extension `.m' for test programs.  Use compilation flags:
          `CPPFLAGS' with `OBJCPP', and both `CPPFLAGS' and `OBJCFLAGS'
          with `OBJC'.

 -- Macro: AC_LANG_PUSH (LANGUAGE)
     Remember the current language (as set by `AC_LANG') on a stack, and
     then select the LANGUAGE.  Use this macro and `AC_LANG_POP' in
     macros that need to temporarily switch to a particular language.

 -- Macro: AC_LANG_POP ([LANGUAGE])
     Select the language that is saved on the top of the stack, as set
     by `AC_LANG_PUSH', and remove it from the stack.

     If given, LANGUAGE specifies the language we just _quit_.  It is a
     good idea to specify it when it's known (which should be the
     case...), since Autoconf detects inconsistencies.

          AC_LANG_PUSH([Fortran 77])
          # Perform some tests on Fortran 77.
          # ...
          AC_LANG_POP([Fortran 77])

 -- Macro: AC_LANG_ASSERT (LANGUAGE)
     Check statically that the current language is LANGUAGE.  You
     should use this in your language specific macros to avoid that
     they be called with an inappropriate language.

     This macro runs only at `autoconf' time, and incurs no cost at
     `configure' time.  Sadly enough and because Autoconf is a two
     layer language (1), the macros `AC_LANG_PUSH' and `AC_LANG_POP'
     cannot be "optimizing", therefore as much as possible you ought to
     avoid using them to wrap your code, rather, require from the user
     to run the macro with a correct current language, and check it
     with `AC_LANG_ASSERT'.  And anyway, that may help the user
     understand she is running a Fortran macro while expecting a result
     about her Fortran 77 compiler...

 -- 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.

   ---------- Footnotes ----------

   (1) Because M4 is not aware of Sh code, especially conditionals,
some optimizations that look nice statically may produce incorrect
results at runtime.


automatically generated by info2www