Typechecking macro arguments in C

Question

Is it possible to typecheck arguments to a #define macro? For example:

typedef enum
{
    REG16_A,
    REG16_B,
    REG16_C
}REG16;

#define read_16(reg16)  read_register_16u(reg16); \
                        assert(typeof(reg16)==typeof(REG16));

The above code doesn't seem to work. What am I doing wrong?

BTW, I am using gcc, and I can guarantee that I will always be using gcc in this project. The code does not need to be portable.

Answer 1

gcc supports typeof

e.g. a typesafe min macro taken from the linux kernel

#define min(x,y) ({ \
    typeof(x) _x = (x); \
    typeof(y) _y = (y); \
    (void) (&_x == &_y);        \
    _x < _y ? _x : _y; })

but it doesn't allow you to compare two types. Note though the pointer comparison which Will generate a warning - you can do a typecheck like this (also from the linux kernel)

#define typecheck(type,x) \
({  type __dummy; \
    typeof(x) __dummy2; \
    (void)(&__dummy == &__dummy2); \
    1; \
})

Presumably you could do something similar - i.e. compare pointers to the arguments.