Selecting C++ language

[Steffen Dettmer]

Hi,

for a project I needed to select C++98. When using g++, this is done
by adding compiler flag "-std=c++98". I liked to have a compiler check
whether this option works.

A web search revealed that this seems not to be intended for maximum
portability; language should not be limited. A similar thread appeared
here for C, but I think the portability argument is wrong. If the
source code is written for C++98, C++98 compiler must be used (only
because standards are mostly backward-compatible, this is not a daily
major issue). Similar with C vs. C++. If someone has no C++ compiler,
he cannot compile the C++ sources. /bin/cat is maximum portable but
supports only the empty subset of needed features :-) so in short, I
think the requirement is right. For C++-98 sources, a C++-98 compiler
must be used. Theoretically it should be "at least", but probably
there are possibilities to write code that behaves differently when
using e.g. c++11, so packages may require /exactly/ c++98, I think.
The package developer needs it to avoid to accidentally use newer
features. Cool would be to couple this to a debug/release mode (but
AFAIK this is not a autoconf concept at all).

How do I configure C++98?

I tried to temporarily set CXXFLAGS and call AC_COMPILE_IFELSE, but
this looks so ugly and is so complex that I think it cannot be right.

Also, my guesswork relies on the assumption that any compiler that
does not moan about "-std=c++98", understands it in the intended way.
Here, it should be obvious, but what's with generic options like "-g",
could be something different on exotic compilers. autoconf detects the
gcc (and I think it sets a variable to use the result), but not g++. I
could assume that c++ is g++ if gcc is present, but that's still an
assumption.

I'm also not sure whether I should I set CXXFLAGS or CPPFLAGS?

I also wanted to support --enable-debug, but I didn't find how to do
that. Is there no standard option or mechanism? For example, I like
-DNDEBUG if --disable-debug etc, but -D may be compiler specific,
config.h may be too late - so what is adviced?

I include my guesswork script for "-std=c++98 auto detection" in the
hope to get criticism.

Thank you for reading this long question!

Regards,
Steffen


AC_INIT([test], [1.0], address@hidden, [test], [])
AC_PREREQ([2.59])

AC_CONFIG_MACRO_DIR([m4])
AM_PATH_CPPUNIT()
LT_INIT
AM_INIT_AUTOMAKE([1.10 -Wall no-define foreign])

AC_PROG_CXX

CPPFLAGS='-I$(top_srcdir)/src'

dnl A function to check if compiler accepts option "-std=c++98" (g++)
AC_DEFUN([AC_STD_CHECK_STD], [
AC_MSG_CHECKING([Compiler flag to use 1998 ISO C++ standard plus amendments])
dnl The 1998 ISO C++ standard plus amendments
AC_SUBST(CXX_ISOCXX98)
CXX_ISOCXX98=-std=c++98
AC_LANG_PUSH(C++)
ac_std_cxx_flags="$CXXFLAGS"
="$CXX_ISOCXX98 $CXXFLAGS"
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], [[]])],
  [ac_std_check_std_result='yes'],
  [ac_std_check_std_result='no'; CXX_ISOCXX98=""])
AC_MSG_RESULT([$ac_std_check_std_result])
CXXFLAGS="$ac_std_cxx_flags"
AC_LANG_POP()
])
AC_STD_CHECK_STD
dnl for the needed files, Makefile.am has a "maude_CXXFLAGS"

AC_CONFIG_HEADERS([config.h])
AC_CONFIG_FILES([Makefile])
AC_OUTPUT