Example of how to implement static assert using template specialisation.

ctassert.h

template<bool> struct _compile_time_assert;
template<> struct _compile_time_assert<true> {};
#define ctassert(expr) if (0) { int flaming_goat_sausage = sizeof(_compile_time_assert<(bool)(expr)>); flaming_goat_sausage++; }

int main (int argc, char *argv[]) {
    ctassert (sizeof (int) == 4);
    ctassert ((sizeof (int) == 5) == false);

    //BLAM
    ctassert (sizeof (int) == 5);
}

/*
eskil@machine:/tmp$ g++ ctassert.cc -Wall -Werror
ctassert.cc: In function ‘int main(int, char**)’:
ctassert.cc:10: error: invalid application of ‘sizeof’ to incomplete type ‘_compile_time_assert<false>’ 
*/