static_assert, _Static_assert − fail compilation if assertion is false
Standard C library (libc)
#include <assert.h>
void static_assert(scalar constant-expression, const char *msg);
/* Since C23: */
void static_assert(scalar
constant-expression);
This macro is similar to assert(3), but it works at compile time, generating a compilation error (with an optional message) when the input is false (i.e., compares equal to zero).
If the input is nonzero, no code is emitted.
msg must be a string literal. Since C23, this argument is optional.
There’s a keyword, _Static_assert(), that behaves identically, and can be used without including <assert.h>.
No value is returned.
In C11, the second argument (msg) was mandatory; since C23, it can be omitted.
C11 and later.
static_assert() can’t be used in some places, like for example at global scope. For that, a macro must_be() can be written in terms of static_assert(). The following program uses the macro to get the size of an array safely.
#include
<assert.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/*
* This macro behaves like static_assert(), failing to
* compile if its argument is not true. However, it always
* returns 0, which allows using it everywhere an expression
* can be used.
*/
#define must_be(e) \
( \
0 * (int) sizeof( \
struct { \
static_assert(e); \
int ISO_C_forbids_a_struct_with_no_members; \
} \
) \
)
#define is_same_type(a, b) \
__builtin_types_compatible_p(typeof(a), typeof(b))
#define is_array(arr) (!is_same_type((arr), &*(arr)))
#define must_be_array(arr) must_be(is_array(arr))
#define sizeof_array(arr) (sizeof(arr) + must_be_array(arr))
#define nitems(arr) (sizeof((arr)) / sizeof((arr)[0]) \
+ must_be_array(arr))
int foo[10];
int8_t bar[sizeof_array(foo)];
int
main(void)
{
for (size_t i = 0; i < nitems(foo); i++) {
foo[i] = i;
}
memcpy(bar, foo, sizeof_array(bar));
for (size_t i = 0; i < nitems(bar); i++) {
printf("%d,", bar[i]);
}
exit(EXIT_SUCCESS);
}
assert(3)