Typecheck macro in C (from Linux Source)

typecheck_macro.c

//Use -Werror in GCC to get error, otherwise it will be a warning

/*
Constraints

One of the following shall hold:

    both operands have arithmetic type;
    both operands are pointers to qualified or unqualified versions of compatible types;
    one operand is a pointer to an object or incomplete type and the other is a pointer to a qualified or unqualified version of      void; or
    one operand is a pointer and the other is a null pointer constant.
*/

#include <stdio.h>

#define typecheck(type, x) \
                 ({ type _z; \
		    typeof(x) _y; \
		    (void)(&_y == &_z); \
		    1; \
		  })

int main(int argc, char* argv[])
{
  printf("%d\n", typecheck(int, 10));
  return 0;
}