#include 
#include 

std::string random_string()
{
     std::string str("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz");

     std::random_device rd;
     std::mt19937 generator(rd());

     std::shuffle(str.begin(), str.end(), generator);

     return str.substr(0, 32);    // assumes 32 < number of characters in str         
}