Compile-time assert on datatype sizes

Question

I would like to perform a compile-time check on datatype sizes in a C/C++ project, and error on unexpected mismatches. Simple

#if sizeof foo_t != sizeof bar_t

does not compile - claims that sizeof is not a proper compile-time constant.

The desired scope of platforms - at the very least Visual C++ with Win32/64, and GCC on x86/amd64.

EDIT: compile-time, not necessarily preprocessor. Just not a run-time error.

EDIT2: the code assumes that wchar_t is 2 bytes. I want a compilation error if it's accidentally compiled with 4-byte wchar's.

Answer 1

in C++11 you can use static assert

static_assert(sizeof(foo_t) == sizeof(bar_t), "sizes do not match");

If it is pre C++11 then you can use boost static assert macro

http://www.boost.org/doc/libs/1_48_0/doc/html/boost_staticassert.html

BOOST_STATIC_ASSERT(sizeof(int)==sizeof(unsigned));
BOOST_STATIC_ASSERT_MSG(sizeof(int)==sizeof(unsigned), "sizes do not match");