[boost] Compiler identification macros (please comment)

From: Gennaro Prota (gennaro_prota_at_[hidden])
Date: 2004-03-22 13:11:27

As recently come up (again) in the threads

    "Comment regarding __GNUC__ spoofing"
    "[config] Patch for Intel 8.0 + Dinkum lib"

boost library developers have often a need to know the exact compiler
in use, but they have no straightforward and easily maintainable way
do that. The issue is that they can't just rely on compiler
"identification" macros, as predefined by each compiler, because those
are not *unique* to each compiler. Two typical cases are __GNUC__,
which is defined both by g++ and Intel for Linux, and _MSC_VER which
is defined by several compilers. A test for "real" g++, for instance,
would look something like

 #if defined(__GNUC__) && !defined(__ICL) && !defined...

which is unnecessarily tedious, error prone and hard to maintain. The
problem would be solved if the config system exposed a macro for each
compiler that it identifies.

There seems to be agreement that this should be done, so please
express your opinion about the names you prefer for the macros, or
tell why you don't want them. I heartedly ask for *short* names,
because preprocessing lines become easily enourmous otherwise (the
typical test has the form: #if defined(MACRO_NAME) && (MACRO_NAME <=
xx)).

Currently, there are 16 config files in boost/config/compiler/ but we
don't need so much macros immediately. So I just propose the following
(other ones can be added on an "as needed" basis):

 BOOST_BORLAND
 BOOST_COMEAU
 BOOST_GNU (1)
 BOOST_INTEL
 BOOST_MSVC (2)

----
Notes:
 (1) since the other macros employ the name of the producing company,
rather than the name of the compiler, BOOST_GNU seems more consistent
than BOOST_GCC (though, of course, GNU is not a "company")
 (2) this is inconsistent, but it already exists. Maybe
BOOST_MICROSOFT, or BOOST_MS, could be provided as a synonym.
Genny.