std :: mt19937不返回随机数 [英] std::mt19937 doesn't return random number

问题描述

我有以下代码:

unsigned int randomInt()
{
    mt19937 mt_rand(time(0));
    return mt_rand();
};

如果我在for循环中调用此代码(例如4000次)，则不会得到随机的无符号整数，而不会得到例如1000次一个值，而接下来的1000次将获得下一个值.

If I call this code, for example 4000 times in a for loop, I don't get random unsigned integers, instead I get for example 1000 times one value and the next 1000 times I get the next value.

我在做什么错了?

推荐答案

之所以会发生这种情况，是因为您在一个循环中调用f 4000次，这可能不到一毫秒，因此每次调用time(0)都会返回相同的结果值，因此使用相同的种子初始化伪随机数生成器.正确的方法是一劳永逸地初始化种子，最好通过std::random_device进行初始化，就像这样:

This happens because you call f 4000 times in a loop, which probably takes less than a mili second, so at each call time(0) returns the same value, hence initializes the pseudo-random generator with the same seed. The correct way is to initialize the seed once and for all, preferably via a std::random_device, like so:

#include <random>
#include <iostream>

static std::random_device rd; // random device engine, usually based on /dev/random on UNIX-like systems
// initialize Mersennes' twister using rd to generate the seed
static std::mt19937 rng(rd()); 

int dice()
{
    static std::uniform_int_distribution<int> uid(1,6); // random dice
    return uid(rng); // use rng as a generator
}

int main()
{
    for(int i = 0; i < 10; ++i)
        std::cout << dice() << " ";   
}

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