Re: Detecting C compiler

[Bob Proulx]

> I'm trying to write a pair of macros to enable strict ansi conformance mode
> and all vaguely useful warnings for at least my target platforms:
> 
> * AIX with Visualage for C++ C compiler (xlc_r)
> * Solaris with Sun's ANSI C compiler (cc)
> * HP-UX with HP's C compiler (cc)
> * Linux with GCC

I am far from being expert in autoconf/automake.  But I just tackled
that same problem not too terribly long ago.  This is what I came up
with.  It is probably wrong for a number of reasons.  I would welcome
a critique from the list.  Note that I am using autoconf and automake
together and so do have the automake macros available.

  AM_PROG_CC_STDC
  if test "$am_cv_prog_cc_stdc" = "no"
  then
    echo "Error: Compiler is not ANSI." 1>&2
    exit 1
  fi
  if test -z "$CC"
  then
    echo "Error: No Compiler found." 1>&2
    exit 1
  fi

I don't like the above because I reached into the internals of the
automake macros to get am_prog_cc_stdc.  But I found no other way.
But since I am generating the confiure script I can guarentee that
they are consistent.  And the failure mode is not too terrible
regardless.

As you can see this is not looking for maximal portability to pre-ANSI
systems.  It just wants to correctly diagnose a non-ANSI system and
state it right up front.

This is drift.  But then if the compiler found is gcc I can turn on
more specific gcc warnings.  But if not then do nothing.

  AC_MSG_CHECKING(for maximum warning verbosity options)
  if test "$GCC" = "yes"
  then
    ac_compile_warnings_opt='-Wall -Wmissing-prototypes -Wstrict-prototypes'
    CFLAGS="$CFLAGS $ac_compile_warnings_opt"
  fi
  ac_compile_warnings_msg="$ac_compile_warnings_msg
  $ac_compile_warnings_opt for C"
  AC_MSG_RESULT($ac_compile_warnings_msg)
  unset ac_compile_warnings_msg
  unset ac_compile_warnings_opt

> The problem is what to do to differentiate between the Sun and HP cc's.

The above fragment works fine on the HP systems.  Not with the bundled
crippled compiler but an ANSI C compiler installed.  But I have not
tested it in the case that neither the HP ANSI C compiler nor the gcc
compilers are installed.  I assume it would work on a Sun as well.  As
you can see nothing in the code says anything particular about either
system.

> I haven't even considered looking at uname and relying on the kernel
> architecture since that breaks the philosophy of autoconf.

Good.  I hate it when people do that.

I am now compiling for ia64 and even if only the config.guess and
config.sub files need to be updated it is still a pain.  But when I
have to dig through configure scripts to tweak the architecture checks
around then I am really in a world of hurt.  Because usually then I
need a specific version of autoconf to regenerate.  In which case I
usually just bypass and edit the generated configure.  The programs
that avoid those architecture checks usually work out of the box
without modification.

Bob