C++ 如何阻止随机引擎产生负数? [英] C++ how to stop a random engine from producing negative numbers?

问题描述

我有一个函数试图生成 18 到 5 之间的随机数

I have a function that im trying to produce random numbers between 18 and 5

int randomAge() {
  int random;
  std::random_device rd;
  static std::default_random_engine generator(rd()); //produce a static random engine
  std::normal_distribution<double> distribution(18, 52);  //random age between 18 and 52
  random = distribution(generator);
  return random;
}

但是，我收到了大于 52 的负数和偶数.我该如何解决这个问题，使其生成 18 到 52 之间的数字?

However I am recieving negative numbers and even numbers that are higher than 52. How can I fix this so it produces numbers between 18 and 52?

推荐答案

您正在使用 std::normal_distribution，它根据正态(或高斯)随机数分布生成随机数.您正在使用 this 构造函数:

You're using std::normal_distribution which generates random numbers according to the Normal (or Gaussian) random number distribution. You're using this constructor:

explicit normal_distribution( RealType mean, RealType stddev = 1.0 );

你想要的是std::uniform_real_distribution.请参阅参考:

产生随机浮点值 i，均匀分布在区间 [a, b)

Produces random floating-point values i, uniformly distributed on the interval [a, b)

请注意，您的引擎和发行版必须是 thread_local(或 static)，并且随机设备可以是临时的.否则，您的结果分布不均匀.您还应该考虑获取一个随机整数而不是 double，因为无论如何返回类型都是 int:

Do note that your engine and distribution must be thread_local (or static) and the random device can be a temporary. Otherwise your results are not uniformly distributed. You should also consider getting a random integer instead of double since the return type is int anyway:

#include <random>

int randomAge() {
  thread_local std::mt19937 engine{ std::random_device{}() };
  thread_local std::uniform_int_distribution<int> distribution{ 18, 52 };
  return distribution(engine);
}

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• 如果我截断输出，Mersenne-twister 加密安全吗?

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