int random string generator c 2b 2b

1 
2string  gen_random(int len) {
3        string s;
4        static const char alphanum[] =
5            "0123456789"
6            "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
7            "abcdefghijklmnopqrstuvwxyz";
8
9        for (int i = 0; i < len; ++i) {
10            s+= alphanum[rand() % (sizeof(alphanum) - 1)];
11             }
12
13     return s;
14