c++我的随机生成器随机生成某些东西，但是每次运行它时它都以相同的顺序执行

所以我做了一个MAC地址生成器。但是随机部分很奇怪。它随机生成一个数字，我用来从数组中选择一些东西。但是每次运行exe。它生成相同的数字。这是我的代码

#include <random>
#include <string>
//Mac Addr example -> 82-F5-4D-72-C1-EA
//6 two char sets
//Dont include spaces/dashes/dots

std::string chars[] = { "A","B","C","D","E","F" };
int nums[] = { 0,1,2,3,4,5,6,7,8,9 };

std::string GenMacAddr()
{
    std::string final;
    std::string CharSet;
    int choice;
    for (int i = 0; i < 6; i++) {
        choice = 1 + rand() % 4;
        if (choice == 1) { //Char Set only int
            for (int x = 0; x < 2; x++) { //Makes action happen twice
                final += std::to_string(nums[rand()%10]);
            }
        }
        else if (choice == 2) { //Char set only str
            for (int x = 0; x < 2; x++) { //Makes action happen twice
                final += chars[rand() % 6];
            }
        }
        else if (choice == 3) {
            final += chars[rand() % 6];
            final += std::to_string(nums[rand() % 10]);
        }
        else if (choice == 4) {
            final += std::to_string(nums[rand() % 10]);
            final += chars[rand() % 6] ;
        }
    }
    
    return final;
}

回答

#include <random>
#include <iostream>

int main() {
    std::random_device random_dev; // Non deterministic random number generator
    std::mt19937 mers_t(random_dev()); // Seed mersenne twister with it .
    std::uniform_int_distribution<int> distribution(0, 100); // Bound the output.

    // Print a random integer in the range [0,100] ( included ) .
    std::cout << distribution(mers_t) << 'n';
}