Question

To check that two variables have the same structure type I use a macro

#define assert_same_struct_types(a, b)    ((void) (sizeof((a)=(b))))

If some function-like macro

#define m(a,b) blablabla

assumes a and b should be of the same structure type, I add a compile time check:

#define m(a,b) (assert_same_struct_types(a, b), blablabla)

which provokes compiler error if caller of m(a,b) accidentally passes to m different types of structs.

However, this approach doesn’t always work for builtin and pointer types due to implicit conversions between them.

So, is it possible to solve this problem for arbitrary types, not necessarily structs?

I need a solution for C89, however, it would be interesting to hear about C99 or C11 possibilities.

Answer 1

#define ASSERT_SAME_TYPE(a, b)  ((void) (&(a) == &(b)))

will get you a compile diagnostic and an error with -Werror (for gcc or a similar option for other compilers).

Note that a lot of compilers have a non standard extension typeof operator to get the type of an object and this can be used to check two types are the same.