C语言 如何同时在多个进程中生成随机数

Question

如何在 C 中为同时运行的多个进程生成随机数？

我想使用 srand 和 rand但我不知道如何（也许使用进程 ID？

Answer 1

您可以根据进程 ID 为每个进程使用不同的种子，例如：

srand(getpid());

然后只需使用rand().

Answer 2

经过多年来自可怜的随机种子的奇怪错误，我最终编写了一个代码来从/dev/urandom中获取随机数，这与用于SSL的随机数相同。 在我的代码中，我使用这些"好"的随机数来播种C stdlib rand（）函数，只要它有一个好的种子，它就足以完成我的任务：

#include <stdio.h>
#include <stdlib.h>
//HOW MANY BITS IN A CHAR? THIS MACRO IS USUALLY DEFINED
#ifndef CHAR_BIT
#define CHAR_BIT 8
#endif
//PATH TO RANDOM NUMBER GENERATOR
const char inPath[]="/dev/urandom";
//EXTRACTS A PSEUDORANDOM unsigned long FROM THE OPERATING SYSTEM VIA /dev/urandom
unsigned long get_urandom(){
  //OPEN INPUT STREAM
  FILE *inFile;
  inFile=fopen(inPath,"r");
  //FAILED TO OPEN STREAM
  if(inFile==NULL){
    fprintf(stderr, "# Failed to open random device %sn", inPath);
    return 0;
  }
  //HOW MANY BITS IN A CHAR? HOW MANY CHARS IN AN UNSIGNED LONG?
  const int bitsInChar  = CHAR_BIT;
  const int charsInLong = sizeof(unsigned long) / sizeof(char);
  //GET RANDOM UNSIGNED LONG ONE CHARACTER AT A TIME
  unsigned long randomSeed=0;
  for(int i=0; i<charsInLong; i++)
    randomSeed |= fgetc(inFile) << i*bitsInChar;
  //CLOSE STREAM AND RETURN
  fclose(inFile);
  return randomSeed;
}
int main(){
  // We can use the above function directly to get our random numbers, but this is slow.
  printf("We can get random numbers from the OS via get_urandom: %un", get_urandom());  
  // Or we can just call get_urandom once, to use as a seed for the stdlib rand() function.
  unsigned int randomSeed=get_urandom();
  srand(randomSeed);
  printf("Or, using a random seed from get_urandom: %un", randomSeed);
  printf("We can get random numbers from stdlib, e.g.: %un", rand());
}

下面是相同的代码，该函数用 C++ 重写：

#include <fstream>
using namespace std;
//HOW MANY BITS IN A CHAR? THIS MACRO IS USUALLY DEFINED
#ifndef CHAR_BIT
#define CHAR_BIT 8
#endif
//EXTRACTS A PSEUDORANDOM unsigned long FROM THE OPERATING SYSTEM VIA /dev/urandom
unsigned long get_urandom(const char inPath[]="/dev/urandom"){
  //OPEN INPUT STREAM
  ifstream inFile(inPath);
  //FAILED TO OPEN STREAM
  if(inFile.fail()){
    fprintf(stderr, "# Failed to open random device %sn", inPath);
    return 0;
  }
  //HOW MANY BITS IN A CHAR? HOW MANY CHARS IN AN UNSIGNED LONG?
  const int bitsInChar  = CHAR_BIT;
  const int charsInLong = sizeof(unsigned long) / sizeof(char);
  //GET RANDOM UNSIGNED LONG ONE CHARACTER AT A TIME
  unsigned long randomSeed=0;
  for(int i=0; i<charsInLong; i++)
    randomSeed |= inFile.get() << i*bitsInChar;
  //CLOSE STREAM AND RETURN
  inFile.close();
  return randomSeed;
}
int main(){
  // We can use the above function directly to get our random numbers, but this is slow.
  printf("We can get random numbers from the OS via get_urandom: %un", get_urandom());  
  // Or we can just call get_urandom once, to use as a seed for the stdlib rand() function.
  unsigned int randomSeed=get_urandom();
  srand(randomSeed);
  printf("Or, using a random seed from get_urandom: %un", randomSeed);
  printf("We can get random numbers from stdlib, e.g.: %un", rand());
}