How to get C compile time #error if a sizeof(struct ...) not equal to a given number?
The question is from programming course, where I'd like to avoid to run miss-sized binary code.
(The sizeof operator, as we know, doesn't work in #if .. #endif directive.)
How to get C compile time #error if a sizeof(struct ...) not equal to a given number?
You cannot, because the pre-processor knows nothing about sizes of types.
You can however static_assert:
static_assert(sizeof(T) == N, "T must have size N")
In C, the keyword is _Static_assert, also available through macro static_assert in <assert.h>.
Don't. You already explained why.
In modern C++ you can write:
static_assert(sizeof(T) == 42);
Although it is better to write code that doesn't care what the size of T is.
#include <assert.h>
//T should have size 10
static_assert(sizeof(T) == 10)
It's available only the latest C compiler
