不同实现之间的随机输出不同 [英] Random output different between implementations

问题描述

我已经使用libstdc ++，libc ++和dinkumware尝试过该程序:

I've tried this program with libstdc++, libc++ and dinkumware:

#include <iostream>
#include <algorithm>
#include <vector>
#include <random>
#include <functional>
#include <limits>

int main()
{
    std::vector<int> v(10);

    std::mt19937 rand{0};
    std::uniform_int_distribution<> dist(
        1, 10
    );

    std::generate_n(v.begin(), v.size(),
        std::bind(dist, rand));

    for (auto i : v)
        std::cout << i << " ";
}

输出分别为:

6 6 8 9 7 9 6 9 5 7 

6 1 4 4 8 10 4 6 3 5 

5 10 4 1 4 10 8 4 8 4 

每次运行的输出都是一致的，但是正如您所看到的，它们是不同的.解释吗?

The output is consistent for each run but as you can see, they're different. Explain?

推荐答案

uniform_int_distribution<>不需要不需要. [rand.dist.general]指定:

There is no required implementation for uniform_int_distribution<>. [rand.dist.general] specifies that:

产生每个指定分布的算法是实现定义的.

The algorithms for producing each of the specified distributions are implementation-defined.

[rand.dist.uni.int]所陈述的全部是:

All that [rand.dist.uni.int] states is:

uniform_int_distribution随机数分布产生随机整数i，a <= i <= b，分布 根据常数离散概率函数 P(i | a, b) = 1/(b − a + 1).

A uniform_int_distribution random number distribution produces random integers i, a <= i <= b, distributed according to the constant discrete probability function P(i | a, b) = 1/(b − a + 1) .

每个实现都可以按照自己的意愿随意实现此分发.您所看到的显然是三种不同的实现.

Each implementation is free to achieve this distribution how it wishes. What you are seeing is apparently three different implementations.

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