One man's quest for the most optimized random password generator that can be made with C++, hopefully this will be useful.

randpw.cpp

#include <chrono>
#include <functional>
#include <iostream>
#include <random>
#include <string>

static void show_usage(std::string name)
{
    std::cerr << "Usage: " << name << " <option(s)>\n"
              << "Options:\n"
              << "\t-h,--help\t\tShow this help message\n"
              << "\t-l,--length LENGTH\tSpecify the password length\n"
              << "\t-s,--seed SEED\t\tUse a unique seed for the random engine\n"
              << "\t-v,--version\t\tOutput the program version\n";
}

int main (int argc, char *argv[])
{
    std::string charset ("abcdefghijklmnopqrstuvwxyz"
                         "ABCDEFGHIJKLMNOPQRSTUVWXYZ" 
                         "1234567890!@#$%^&*()");
    int length = 16;
    std::default_random_engine generator;
    std::uniform_int_distribution<int> distribution (0, (int) charset.size() - 1);
    generator.seed (std::chrono::system_clock::now().time_since_epoch().count());

    if (argc >= 2) {
        for (int i = 1; i < argc; i++) {
            std::string arg = argv[i];
            if ((arg ==  "-l") || (arg == "--length")) {
                if (i + 1 < argc) {
                    length = atoi(argv[++i]);
                } else {
                    std::cerr << "-l,--length takes one argument" << std::endl;
                    return 1;
                }
            } else if ((arg == "-s") || (arg == "--seed")) {
                if (i + 1 < argc) {
                    std::string str (argv[++i]);
                    std::seed_seq seed (str.begin(), str.end());
                    generator.seed (seed);
                } else {
                    std::cerr << "-s,--seed takes one argument" << std::endl;
                    return 1;
                }
            } else if ((arg == "-h") || (arg == "--help")) {
                show_usage(argv[0]);
                return 0;
            } else if ((arg == "-v") || (arg == "--version")) {
                std::cout << "Version 0.0.1" << std::endl;
                return 0;
            }
        }
    }

    auto randchar = std::bind (distribution, generator);
    std::string password;
    password.resize(length);

    for (int i = 0; i < length; i++) {
        password.at(i) = charset.at(randchar());
    }

    std::cout << password << std::endl;
    return 0;
}