每次在C ++中生成相同的随机数

Question

这是我的代码：

int main(int argc, char** argv) {

    int sleeptime = atoi(argv[1]);    
    int sleepCount = atoi(argv[2]);

    int sleepTimeRandom = 1 + (rand() % (int)(sleeptime));
    int sleepCountRandom = 1 + (rand() % (int)(sleepCount));

    sleepTimeRandom = sleepTimeRandom * 1000;

    DWORD id = GetCurrentProcessId();

    cout << "\n\nProcess with id " << id << " will sleep for " << sleepTimeRandom << " milliseconds\n";
    cout << "\n\nProcess with id " << id << " will sleep " << sleepCountRandom << " times \n";

当我打电话给exe时

sleeper 4 4 

我总是得到2000毫秒，4次......为什么？

Answer 1

您必须为随机数生成器播种。 see here for an example

未seeded.c

#include <stdio.h>
#include <stdlib.h>

int main ()
{
  printf ("Random not seeded: %d\n", rand()%10);
  return 0;
}

非种子输出

Random not seeded: 3
Random not seeded: 3
Random not seeded: 3
Random not seeded: 3
Random not seeded: 3

seeded.c

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main ()
{
  srand(time(NULL));
  printf ("Random seeded: %d\n", rand()%10);
  return 0;
}

种子输出

Random fast seeded: 7
Random fast seeded: 7
Random fast seeded: 7
Random fast seeded: 1
Random fast seeded: 1
Random fast seeded: 1
Random fast seeded: 5
Random fast seeded: 5
Random fast seeded: 5
Random fast seeded: 5

快速seeded.c

如果您希望能够每秒多次调用您的实用程序，则必须使用不同的来源为您播种，否则您最终会得到一些重复的随机数。

这是一个使用纳秒而不是time()的示例，它只返回秒。

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main ()
{
    struct timespec ts;
    clock_gettime(CLOCK_MONOTONIC, &ts);

    /* using nano-seconds instead of seconds */
    srand((time_t)ts.tv_nsec);

    printf ("Random fast seeded: %d\n", rand()%10);
    return 0;
}

快速种子输出

您可以在此处看到，这些数字的分组与前一个示例不同。

Random fast seeded: 9
Random fast seeded: 6
Random fast seeded: 5
Random fast seeded: 6
Random fast seeded: 1
Random fast seeded: 1
Random fast seeded: 9
Random fast seeded: 4
Random fast seeded: 3
Random fast seeded: 2

均匀分布的随机数

如果您对均匀分布的随机数感兴趣，请在下面看到 user3003631 的答案。如果你实际上在使用C ++，那就是我建议做随机数的方法。 More information here too on this.

Answer 2

C ++中还有随机效用 如果你想要一个不同的方法......可能更高的质量 请原谅最低限度的解释

#include <iostream>
#include <algorithm>
#include <random>

int random_test_200()
{
    std::random_device rd;
    uniform_int_distribution<int> ud(1,9);
    mt19937 mt(rd());
    std::vector<int> v1;
    for (int i = 0; i < 40; ++i)
    {
        auto x = ud(mt);
        v1.push_back(x);
    }
}

Answer 3

您需要使用time（）函数为随机数生成器设定种子，以确保RNG以类似随机的方式运行。在开始生成随机数之前添加srand（）调用。