// Generate a random sequence of characters:
// 0-9
// A-Z
// a-z
// -,_

#include <random>
#include <cstdlib>
#include <iostream>
int main(int argc, char * argv[])
{
  // Default length: 16
  // Minimum length: 1
  int length;
  if(argc > 1) length = std::atoi(argv[1]);
  if(length < 1) length = 16;

  // Seed the pseudo-random generator with some actual randomness
  std::mt19937 prand;
  {
    std::random_device rd;
    prand.seed( rd() );
  }

  // Generate random integers in the range [0, 63]
  std::uniform_int_distribution<char> range(0, 63);
  for(int i = 0; i < length; ++i)
  {
    // Transform the integer into acceptable characters
    char next = range(prand);
    // 0-9
    if(next < 10) std::cout << char(next + 48);
    // A-Z
    else if(next < 36) std::cout << char(next + 55);
    // a-z
    else if(next < 62) std::cout << char(next + 61);
    // -
    else if(next < 63) std::cout << '-';
    // _
    else std::cout << '_';
  }
  std::cout << std::endl;

  return 0;
}