http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54454
--- Comment #1 from mikulas at artax dot karlin.mff.cuni.cz 2012-09-02 01:52:54 UTC --- Another specification violation: section 6.7.2.1 paragraph 20 says that assignment of a structure with flexible array member doesn't copy any of the array elements. In gcc it is buggy because it copies some array elements. Try this: #include <stdio.h> #include <stdlib.h> #include <string.h> struct flexible { unsigned a; unsigned short b; unsigned char array[]; }; int main(void) { struct flexible *f1, *f2; f1 = malloc(sizeof(struct flexible) + 3); f1->array[0] = 0; f1->array[1] = 0; f1->array[2] = 0; f2 = malloc(sizeof(struct flexible) + 3); f2->array[0] = 1; f2->array[1] = 1; f2->array[2] = 1; *f2 = *f1; printf("f2->array[0] == %d (should be 1)\n", f2->array[0]); printf("f2->array[1] == %d (should be 1)\n", f2->array[1]); printf("f2->array[2] == %d (should be 1)\n", f2->array[2]); return 0; }