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#include <stdio.h>
 
#define STATIC_ASSERT(COND) typedef char static_assertion_##__LINE__[(COND) ? 1 : -1]
#define ENSURE_SIZE(structure, size) STATIC_ASSERT(sizeof(structure) == size)
 
typedef struct
{
	unsigned b0 : 1;
	unsigned b1 : 1;
	unsigned b2 : 1;
	unsigned b3 : 1;
	unsigned b4 : 1;
	unsigned b5 : 1;
	unsigned b6 : 1;
	unsigned b7 : 1;
	unsigned b8 : 1;
	unsigned b9 : 1;
	unsigned b10 : 1;
	unsigned b11 : 1;
	unsigned b12 : 1;
	unsigned b13 : 1;
	unsigned b14 : 1;
	unsigned b15 : 1;
	unsigned b16 : 1;
	unsigned b17 : 1;
	unsigned b18 : 1;
	unsigned b19 : 1;
	unsigned b20 : 1;
	unsigned b21 : 1;
	unsigned b22 : 1;
	unsigned b23 : 1;
	unsigned b24 : 1;
	unsigned b25 : 1;
	unsigned b26 : 1;
	unsigned b27 : 1;
	unsigned b28 : 1;
	unsigned b29 : 1;
	unsigned b30 : 1;
	unsigned b31 : 1;
	unsigned b32 : 1;
} foo;
ENSURE_SIZE(foo, sizeof(unsigned));
 
int main(void) {
	return 0;
}
 

prog.c:3:42: error: size of array 'static_assertion___LINE__' is negative
 #define STATIC_ASSERT(COND) typedef char static_assertion_##__LINE__[(COND) ? 1 : -1]
                                          ^
prog.c:4:38: note: in expansion of macro 'STATIC_ASSERT'
 #define ENSURE_SIZE(structure, size) STATIC_ASSERT(sizeof(structure) == size)
                                      ^
prog.c:42:1: note: in expansion of macro 'ENSURE_SIZE'
 ENSURE_SIZE(foo, sizeof(unsigned));
 ^

Standard output is empty