To be fair, MSVC has the most C99 stuffs. What is mainly missing for porting (my) programs is the native complex number. But we have Intel compiler for free on Windows, which is fully compatible with the C/C++ standard and produces faster binaries.

The C++ frontend of MSVC handles (the common) compiler-specific language extensions differently than the other compilers. Besides, its pre-processor behaves differently too. It is now good that there is a clang frontend for MSVC.