Flexible array members in flexible array members are allowed

flexible-in-flexible.c

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct a {
	char x;
	char buf[];
};

struct b {
	char y;
	struct a fub[];
};

int
main(void)
{
	int len_fub = 5;
	int len_buf = 2;

	size_t sz = sizeof(struct b) + len_fub * (sizeof(struct a) + len_buf);
	struct b *p = malloc(sz);

	printf("sizeof(struct a) = %d\n", (int)sizeof(struct a));
	printf("sizeof(struct b) = %d\n", (int)sizeof(struct b));
	printf("*p is size %d\n", (int)sz);

	memcpy(p, "123456789ABCDEF", sz);

	assert('1' == p->y);
	assert('2' == p->fub[0].x);
	assert('3' == p->fub[0].buf[0]);
	assert('4' == p->fub[0].buf[1]);
	assert('4' == p->fub[1].buf[0]);

	return 0;
}