How do I create a random alpha-numeric string in C++?

Question

I'd like to create a random string, consisting of alpha-numeric characters. I want to be able to be specify the length of the string.

How do I do this in C++?

Answer 1

Mehrdad Afshari's answer would do the trick, but I found it a bit too verbose for this simple task. Look-up tables can sometimes do wonders:

#include <iostream>
#include <ctime>
#include <unistd.h>

using namespace std;

string gen_random(const int len) {
    
    string tmp_s;
    static const char alphanum[] =
        "0123456789"
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        "abcdefghijklmnopqrstuvwxyz";
    
    srand( (unsigned) time(NULL) * getpid());

    tmp_s.reserve(len);

    for (int i = 0; i < len; ++i) 
        tmp_s += alphanum[rand() % (sizeof(alphanum) - 1)];
    
    
    return tmp_s;
    
}

int main(int argc, char *argv[]) {
    
    cout << gen_random(12) << endl;
    
    return 0;
}