rand()不返回随机值

Question

它是一个生成随机厄米特矩阵厄米特矩阵的小代码.

我在每次调用rand()之前调用了srand().但输出中仍然没有随机性.

我使用c99的复杂数据类型功能来创建一个埃尔米特矩阵.我不确定我错在哪里:(

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

#define MATSIZE 5
#define RAND_RANGE 100

double complex mat[MATSIZE][MATSIZE];

void gen_mat()
{
  int i =0,j;
  int real;
  int img;
  for( ;i < MATSIZE; i++)
  {
    srand(time(NULL));
    real = rand()%RAND_RANGE + 1;
    srand(time(NULL));
    img = rand()%RAND_RANGE + 1;
    for(j = MATSIZE; j != i ; j--) 
    { 
       mat[i][j] = real + img * I;
       mat[j][i] = conj(mat[i][j]);
    }
    srand(time(NULL));
    if(i == j)
      mat[i][i] = rand()%RAND_RANGE + 0*I;
  }
}

void print_mat()
{
  int i,j;
  for(i = 0; i < MATSIZE; i++)
  {
    for(j = 0; j < MATSIZE; j++)
    {
      printf("%f + %f *i", creal(mat[i][j]), cimag(mat[i][j]));
      printf("    ");
    }
    puts("\n");
  }
}

int main()
{
  gen_mat();
  print_mat();
  return 0;
}

样本输出

[aft@centos-c physics-numaric]$ ./a.out 
66.000000 + 0.000000 *i    67.000000 + 67.000000 *i    67.000000 + 67.000000 *i             67.000000 + 67.000000 *i    67.000000 + 67.000000 *i    

67.000000 + -67.000000 *i    66.000000 + 0.000000 *i    67.000000 + 67.000000 *i      67.000000 + 67.000000 *i    67.000000 + 67.000000 *i    

67.000000 + 67.000000 *i    67.000000 + -67.000000 *i    66.000000 + 0.000000 *i    67.000000 + 67.000000 *i    67.000000 + 67.000000 *i    

67.000000 + 67.000000 *i    67.000000 + -67.000000 *i    67.000000 + -67.000000 *i    66.000000 + 0.000000 *i    67.000000 + 67.000000 *i    

67.000000 + 67.000000 *i    67.000000 + -67.000000 *i    67.000000 + -67.000000 *i      67.000000 + -67.000000 *i    66.000000 + 0.000000 *i    

在main()中编辑调用srand实际上解决了问题.感谢你们.

[aft@centos-c physics-numaric]$ ./a.out 
31.000000 + 0.000000 *i    81.000000 + 75.000000 *i    81.000000 + 75.000000 *i     81.000000 + 75.000000 *i    81.000000 + 75.000000 *i    

81.000000 + -75.000000 *i    53.000000 + 0.000000 *i    69.000000 + 57.000000 *i    69.000000 + 57.000000 *i    69.000000 + 57.000000 *i    

69.000000 + 57.000000 *i    69.000000 + -57.000000 *i    27.000000 + 0.000000 *i    93.000000 + 11.000000 *i    93.000000 + 11.000000 *i    

93.000000 + 11.000000 *i    69.000000 + -57.000000 *i    93.000000 + -11.000000 *i    58.000000 + 0.000000 *i    76.000000 + 78.000000 *i    

76.000000 + 78.000000 *i    69.000000 + -57.000000 *i    93.000000 + -11.000000 *i    76.000000 + -78.000000 *i    67.000000 + 0.000000 *i    

Answer 1

srand每次打电话前都不要打电话rand.程序启动时调用一次.

Answer 2

srand如果循环不要在里面调用.只打电话一次.

srand(time(NULL));
for( ;i < MATSIZE; i++)
{
    // ... calls to rand()   
}

否则,您使用相同的种子为随机生成器播种(因为它足够快以获得相同的时间)

BTW,很多次我觉得为程序/序列创建初始化函数非常传统,我初始化很多东西,包括随机生成(例如调用srand())