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ac-archive: ax_cflags_<option> macros...

From: Guido Draheim
Subject: ac-archive: ax_cflags_<option> macros...
Date: Mon, 06 Jan 2003 02:37:41 +0100
User-agent: Mozilla/5.0 (X11; U; Linux i686; de-AT; rv:1.1) Gecko/20020826

I did lately needed again extensions of the old scheme to add
compiler-specific options. The macros being most in usage
  ac_prog_cc_warnings.m4 (renamed to) vl_prog_cc_warnings.m4
  ac_prog_cc_no_writeable_strings.m4  (needed widely around, and)
  ac_check_cc_opt.m4 (to add arbritrary long-options to gcc/others).

Looking at the implementation bits, we see quite different
approaches at detecting the correct option for the compiler
currently under test. An even different scheme can be seen
in the -ansi detection in the autoconf base macros for the

From these, I did start to invent a different detection scheme
that is hopefully generic enough to add step-by-step more
ac-macros that can add compiler-specific options intended for
the same compile-scheme that the programmers want to have.

It basically picks up the for-list scheme from AC_PROG_CC_STDC
and extends it - the list items contain "%" separator marks
that will mark breaks in the option strings. Each option to
be tested has a _selector test_ - in other words, all compilers
but one shall error-out on these selectors. The selector
options however will not be part of the resulting option
string for the feature that is wished for.

These selector-tests are usually derived from the different
schemes that enable ansi-constraints for the compilers, now
just have a look at the following example take up from

for ac_arg dnl
in "-pedantic  % -Wall"       dnl   GCC
   "-xstrconst % -v"          dnl Solaris C
   "-std1      % -verbose -w0 -warnprotos" dnl Digital Unix
   "-qlanglvl=ansi % -qsrcmsg -qinfo=all:noppt:noppc:noobs:nocnd" dnl AIX
   "-ansi -ansiE % -fullwarn" dnl IRIX
   "+ESlit     % +w1"         dnl HP-UX C
   "-Xc        % -pvctl[,]fullmsg" dnl NEC SX-5 (Super-UX 10)
   "-h conform % -h msglevel 2" dnl Cray C (Unicos)
do CFLAGS="$ac_save_CFLAGS "`echo $ac_arg | sed -e 's,%%.*,,' -e 's,%,,'`
   AC_TRY_COMPILE([],[return 0;],
   [ac_cv_cflags_warn_all=`echo $ac_arg | sed -e 's,.*% *,,'`

The reason: some compilers will happily accept "-v" or "+w1" for
something not intended - they are valid but they do not do what
we want, to just enable additional warning-options.

With this scheme, I have reworked the existing macros that I do
use widely to pick up this detection, and furthermore I did change
them all to a common result-scheme - they add to CFLAGS or CXXFLAGS
when no output-variable has been given as an argument. Note that
each of the following files contains two macros, one for adding to
CFLAGS (AX_CFLAGS_...) and one for C++ flags (AX_CXXFLAGS_...)

hints? comments? objections? ;-)

-- cheers, guido               

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