ax_cflags_gcc_option

AX_CFLAGS_GCC_OPTION(-fvomit-frame) would show a message as like "checking CFLAGS for gcc -fvomit-frame ... yes" and adds the optionflag to CFLAGS if it is understood. You can override the shellvar-default of CFLAGS of course. The order of arguments stems from the explicit macros like AX_CFLAGS_WARN_ALL.

The cousin AX_CXXFLAGS_GCC_OPTION would check for an option to add to CXXFLAGS - and it uses the autoconf setup for C++ instead of C (since it is possible to use different compilers for C and C++).

The macro is a lot simpler than any special AX_CFLAGS_* macro (or ac_cxx_rtti.m4 macro) but allows to check for arbitrary options. However, if you use this macro in a few places, it would be great if you would make up a new function-macro and submit it to the ac-archive.

- $1 option-to-check-for : required ("-option" as non-value)
- $2 shell-variable-to-add-to : CFLAGS (or CXXFLAGS in the other case)
- $3 action-if-found : add value to shellvariable
- $4 action-if-not-found : nothing

note: in earlier versions, $1-$2 were swapped. We try to detect the situation and accept a $2=~/-/ as being the old option-to-check-for.

also: there are other variants that emerged from the original macro variant which did just test an option to be possibly added. However, some compilers accept an option silently, or possibly for just another option that was not intended. Therefore, we have to do a generic test for a compiler family. For gcc we check "-pedantic" being accepted which is also understood by compilers who just want to be compatible with gcc even when not being made from gcc sources.

see also:
       AX_CFLAGS_SUN_OPTION               AX_CFLAGS_HPUX_OPTION
       AX_CFLAGS_AIX_OPTION               AX_CFLAGS_IRIX_OPTION

AC_DEFUN([AX_CFLAGS_GCC_OPTION_OLD], [dnl
AS_VAR_PUSHDEF([FLAGS],[CFLAGS])dnl
AS_VAR_PUSHDEF([VAR],[ac_cv_cflags_gcc_option_$2])dnl
AC_CACHE_CHECK([m4_ifval($1,$1,FLAGS) for gcc m4_ifval($2,$2,-option)],
VAR,[VAR="no, unknown"
 AC_LANG_SAVE
 AC_LANG_C
 ac_save_[]FLAGS="$[]FLAGS"
for ac_arg dnl
in "-pedantic  % m4_ifval($2,$2,-option)"  dnl   GCC
   #
do FLAGS="$ac_save_[]FLAGS "`echo $ac_arg | sed -e 's,%%.*,,' -e 's,%,,'`
   AC_TRY_COMPILE([],[return 0;],
   [VAR=`echo $ac_arg | sed -e 's,.*% *,,'` ; break])
done
 FLAGS="$ac_save_[]FLAGS"
 AC_LANG_RESTORE
])
case ".$VAR" in
     .ok|.ok,*) m4_ifvaln($3,$3) ;;
   .|.no|.no,*) m4_ifvaln($4,$4) ;;
   *) m4_ifvaln($3,$3,[
   if echo " $[]m4_ifval($1,$1,FLAGS) " | grep " $VAR " 2>&1 >/dev/null
   then AC_RUN_LOG([: m4_ifval($1,$1,FLAGS) does contain $VAR])
   else AC_RUN_LOG([: m4_ifval($1,$1,FLAGS)="$m4_ifval($1,$1,FLAGS) $VAR"])
                      m4_ifval($1,$1,FLAGS)="$m4_ifval($1,$1,FLAGS) $VAR"
   fi ]) ;;
esac
AS_VAR_POPDEF([VAR])dnl
AS_VAR_POPDEF([FLAGS])dnl
])


dnl the only difference - the LANG selection... and the default FLAGS

AC_DEFUN([AX_CXXFLAGS_GCC_OPTION_OLD], [dnl
AS_VAR_PUSHDEF([FLAGS],[CXXFLAGS])dnl
AS_VAR_PUSHDEF([VAR],[ac_cv_cxxflags_gcc_option_$2])dnl
AC_CACHE_CHECK([m4_ifval($1,$1,FLAGS) for gcc m4_ifval($2,$2,-option)],
VAR,[VAR="no, unknown"
 AC_LANG_SAVE
 AC_LANG_CXX
 ac_save_[]FLAGS="$[]FLAGS"
for ac_arg dnl
in "-pedantic  % m4_ifval($2,$2,-option)"  dnl   GCC
   #
do FLAGS="$ac_save_[]FLAGS "`echo $ac_arg | sed -e 's,%%.*,,' -e 's,%,,'`
   AC_TRY_COMPILE([],[return 0;],
   [VAR=`echo $ac_arg | sed -e 's,.*% *,,'` ; break])
done
 FLAGS="$ac_save_[]FLAGS"
 AC_LANG_RESTORE
])
case ".$VAR" in
     .ok|.ok,*) m4_ifvaln($3,$3) ;;
   .|.no|.no,*) m4_ifvaln($4,$4) ;;
   *) m4_ifvaln($3,$3,[
   if echo " $[]m4_ifval($1,$1,FLAGS) " | grep " $VAR " 2>&1 >/dev/null
   then AC_RUN_LOG([: m4_ifval($1,$1,FLAGS) does contain $VAR])
   else AC_RUN_LOG([: m4_ifval($1,$1,FLAGS)="$m4_ifval($1,$1,FLAGS) $VAR"])
                      m4_ifval($1,$1,FLAGS)="$m4_ifval($1,$1,FLAGS) $VAR"
   fi ]) ;;
esac
AS_VAR_POPDEF([VAR])dnl
AS_VAR_POPDEF([FLAGS])dnl
])

dnl -------------------------------------------------------------------------

AC_DEFUN([AX_CFLAGS_GCC_OPTION_NEW], [dnl
AS_VAR_PUSHDEF([FLAGS],[CFLAGS])dnl
AS_VAR_PUSHDEF([VAR],[ac_cv_cflags_gcc_option_$1])dnl
AC_CACHE_CHECK([m4_ifval($2,$2,FLAGS) for gcc m4_ifval($1,$1,-option)],
VAR,[VAR="no, unknown"
 AC_LANG_SAVE
 AC_LANG_C
 ac_save_[]FLAGS="$[]FLAGS"
for ac_arg dnl
in "-pedantic  % m4_ifval($1,$1,-option)"  dnl   GCC
   #
do FLAGS="$ac_save_[]FLAGS "`echo $ac_arg | sed -e 's,%%.*,,' -e 's,%,,'`
   AC_TRY_COMPILE([],[return 0;],
   [VAR=`echo $ac_arg | sed -e 's,.*% *,,'` ; break])
done
 FLAGS="$ac_save_[]FLAGS"
 AC_LANG_RESTORE
])
case ".$VAR" in
     .ok|.ok,*) m4_ifvaln($3,$3) ;;
   .|.no|.no,*) m4_ifvaln($4,$4) ;;
   *) m4_ifvaln($3,$3,[
   if echo " $[]m4_ifval($2,$2,FLAGS) " | grep " $VAR " 2>&1 >/dev/null
   then AC_RUN_LOG([: m4_ifval($2,$2,FLAGS) does contain $VAR])
   else AC_RUN_LOG([: m4_ifval($2,$2,FLAGS)="$m4_ifval($2,$2,FLAGS) $VAR"])
                      m4_ifval($2,$2,FLAGS)="$m4_ifval($2,$2,FLAGS) $VAR"
   fi ]) ;;
esac
AS_VAR_POPDEF([VAR])dnl
AS_VAR_POPDEF([FLAGS])dnl
])


dnl the only difference - the LANG selection... and the default FLAGS

AC_DEFUN([AX_CXXFLAGS_GCC_OPTION_NEW], [dnl
AS_VAR_PUSHDEF([FLAGS],[CXXFLAGS])dnl
AS_VAR_PUSHDEF([VAR],[ac_cv_cxxflags_gcc_option_$1])dnl
AC_CACHE_CHECK([m4_ifval($2,$2,FLAGS) for gcc m4_ifval($1,$1,-option)],
VAR,[VAR="no, unknown"
 AC_LANG_SAVE
 AC_LANG_CXX
 ac_save_[]FLAGS="$[]FLAGS"
for ac_arg dnl
in "-pedantic  % m4_ifval($1,$1,-option)"  dnl   GCC
   #
do FLAGS="$ac_save_[]FLAGS "`echo $ac_arg | sed -e 's,%%.*,,' -e 's,%,,'`
   AC_TRY_COMPILE([],[return 0;],
   [VAR=`echo $ac_arg | sed -e 's,.*% *,,'` ; break])
done
 FLAGS="$ac_save_[]FLAGS"
 AC_LANG_RESTORE
])
case ".$VAR" in
     .ok|.ok,*) m4_ifvaln($3,$3) ;;
   .|.no|.no,*) m4_ifvaln($4,$4) ;;
   *) m4_ifvaln($3,$3,[
   if echo " $[]m4_ifval($2,$2,FLAGS) " | grep " $VAR " 2>&1 >/dev/null
   then AC_RUN_LOG([: m4_ifval($2,$2,FLAGS) does contain $VAR])
   else AC_RUN_LOG([: m4_ifval($2,$2,FLAGS)="$m4_ifval($2,$2,FLAGS) $VAR"])
                      m4_ifval($2,$2,FLAGS)="$m4_ifval($2,$2,FLAGS) $VAR"
   fi ]) ;;
esac
AS_VAR_POPDEF([VAR])dnl
AS_VAR_POPDEF([FLAGS])dnl
])

AC_DEFUN([AX_CFLAGS_GCC_OPTION],[ifelse(m4_bregexp([$2],[-]),-1,
[AX_CFLAGS_GCC_OPTION_NEW($@)],[AX_CFLAGS_GCC_OPTION_OLD($@)])])

AC_DEFUN([AX_CXXFLAGS_GCC_OPTION],[ifelse(m4_bregexp([$2],[-]),-1,
[AX_CXXFLAGS_GCC_OPTION_NEW($@)],[AX_CXXFLAGS_GCC_OPTION_OLD($@)])])