acx_f77_cmain_fflags

This macro figures out if extra Fortran compiler flags are required in order to use the Fortran linker to link programs where the main() function is defined via C (or other language). On some systems, notably the Alpha with Compaq compilers, the Fortran libraries have their own main() function which must be disabled.

Runs ACTION-IF-SUCCEED if successful, and ACTION-IF-FAIL if not. Defines the output variable F77_CMAIN_FFLAGS to any discovered flags. (If ACTION-IF-FAIL is not specified, defaults to halting with an error.)

This macro is especially useful in conjunction with automake, since by default automake uses $F77 to link programs mixing C and Fortran, leading to a link error on some systems. In this case, you should set the FFLAGS for that program to include F77_CMAIN_FFLAGS.

AC_DEFUN([ACX_F77_CMAIN_FFLAGS],
[AC_CACHE_CHECK([for f77 flags to use C main function], acx_cv_f77_cmain_fflags,
[acx_cv_f77_cmain_fflags="unknown"
AC_LANG_PUSH(C)
AC_COMPILE_IFELSE([[int main(void) { return 0; }]],
		  [mv conftest.$ac_objext conftest_cmain.$ac_objext],
		  [acx_cv_f77_cmain_fflags=error])
AC_LANG_POP(C)
if test "x$acx_cv_f77_cmain_fflags" != xerror; then
    AC_LANG_PUSH(Fortran 77)
    acx_save_LIBS=$LIBS
    LIBS="conftest_cmain.$ac_objext $LIBS"
    acx_save_FFLAGS=$FFLAGS
    for acx_flag in none -nofor_main; do
	case $acx_flag in
	    none) FFLAGS=$acx_save_FFLAGS ;;
	    *)    FFLAGS="$acx_save_FFLAGS $acx_flag" ;;
	esac
	AC_LINK_IFELSE([
      subroutine foobar()
      return
      end
], [acx_cv_f77_cmain_fflags=$acx_flag; break]);
    done
    FFLAGS=$acx_save_FFLAGS
    LIBS=$acx_save_LIBS
    AC_LANG_POP(Fortran 77)
fi])
    case $acx_cv_f77_cmain_fflags in
	error|unknown)
	    F77_CMAIN_FFLAGS=""
	    ifelse([$2],,[AC_MSG_ERROR([cannot link C main with Fortran])],[$2])
	    ;;
	*)
	    if test "x$acx_cv_f77_cmain_fflags" = xnone; then
		F77_CMAIN_FFLAGS=""
	    else
		F77_CMAIN_FFLAGS="$acx_cv_f77_cmain_fflags"
	    fi
	    $1
	    ;;
    esac
    AC_SUBST(F77_CMAIN_FFLAGS)
])