static_assert

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< c‎ | error
Defined in header <assert.h>
#define static_assert _Static_assert

This convenience macro expands to the keyword _Static_assert

[edit] Example

#include <assert.h>
int main(void)
{
    static_assert(2 + 2 == 4, "2+2 isn't 4");      // well-formed
    static_assert(sizeof(int) < sizeof(char),
                 "this program requires that int is less than char"); // compile-time error
}