I understand that BOOST_MSVC is needed to detect MSVC because other compilers besides MSVC define _MSC_VER.

But what about #ifdefing #pragma warning, should it use _MSC_VER or BOOST_MSVC? The reason why the ifdefing is needed is to prevent GCC and other compilers issuing a warning about #pragma warning, but presumably compilers that have _MSC_VER defined wouldn't warn about that, would they?

Well one would hope not, but I'm not so sure about Como, and even Borland used to define _MSC_VER at one point - and they definitely didn't support that pragma! My gut feeling is that if BOOST_MSVC is available then make use of it, but I could be wrong... John.