如何创建具有随机数据成员值的对象？ C++

Question

下面代码生成的所有对象都具有相同的 randomNumber1 和 randomNumber2 值。如何正确使用 std::default_random_engine？

#include <random>
#include <iostream>

class Food{

    public:
        int randomNumber1;
        int randomNumber2;
        Food(){
            std::default_random_engine generator;
            std::uniform_int_distribution<int> distribution(1,40);
            std::uniform_int_distribution<int> distribution2(1,30);
            randomNumber1 = distribution(generator) * 20;
            randomNumber2 = distribution2(generator) * 20;
        };
};

int main(){

    Food * food = new Food();
    std::cout << food->randomNumber1 << " " << food->randomNumber2 << std::endl;
    Food * food1 = new Food();
    std::cout << food1->randomNumber1 << " " << food1->randomNumber2 << std::endl;
    Food * food2 = new Food();
    std::cout << food2->randomNumber1 << " " << food2->randomNumber2 << std::endl;

    return 0;
};

Answer 1

这是因为您每次创建 Food 对象时都会重新播种 engine（使用相同的种子）。你可以做的是把它设为static，这样它只会播种一次：

static std::default_random_engine generator;
std::uniform_int_distribution<int> distribution(1,40);
std::uniform_int_distribution<int> distribution2(1,30);
randomNumber1 = distribution(generator) * 20;
randomNumber2 = distribution2(generator) * 20;

或者..让调用者决定种子。

或者，正如 @Unimportant 在 cmets 中所说，使用 std::random_device：

static std::random_device dev;
static std::default_random_engine generator(dev());