Flexible array member

flexible_array_member.c

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

typedef struct string
{
    int length;
    char chars[];
} string;

int main(int argc, char * argv[])
{
    int len = sizeof(string) + 10;
    char buf[len];

    string *s = (string*)buf;
    s->length = 9;
    strcpy(s->chars, "123456789");

    printf("%d\n%s\n", s->length, s->chars);

    return EXIT_SUCCESS;
}

flexible_array_member_copy.c

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

typedef struct string
{
    int length;
    char chars[];
} string;

int main(int argc, char * argv[])
{
    int len = sizeof(string) + 10;
    char buf[len];

    string *s = (string*)buf;
    s->length = 10;
    strcpy(s->chars, "123456789");

    string s2 = *s;                          // copy struct string s
    printf("%d\n%s\n", s2.length, s2.chars); // s2.length is copied, s2.chars is not
    return EXIT_SUCCESS;
}