c - 动态矩阵分配程序

Question

我正在学习 C。我有一个程序，可以使用 rand() 动态创建和填充两个矩阵 X 和 Y，并使用随机数，如下所示

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

void main(){

 int i, j, k, m, n;
 double **x;
 double **y;
 printf("Enter a number as the size of two square matrices\n");
 scanf("%d", &m);
 x = (double**)malloc(m * sizeof(double));  
 y = (double**)malloc(m * sizeof(double));
 /* initialize random seed: */
 srand(time(NULL));
 for(i = 0; i < m; i++) {
    x[i] = (double*)malloc(m * sizeof(double));
    y[i] = (double*)malloc(m * sizeof(double));
    for(i = 0; i < m; i++) {
        for(j = 0; j < m; j++) {
            x[i][j] = rand();
            y[i][j] = rand();
        }
        printf("\n");
    }
  }
  printf("\n\n");
}

当我运行这个程序并给出 2 作为矩阵大小时，我看到“段错误”错误。请注意，这个想法是用 double 类型的随机元素填充两个矩阵。让我知道上面的代码是否正确。

更正:编辑1

 x = (double**)malloc(m * sizeof(double*)); 
 y = (double**)malloc(m * sizeof(double*));
 /* initialize random seed: */
 srand(time(NULL));
 for(i = 0; i < m; i++) {
    x[i] = (double*)malloc(m * sizeof(double));
    y[i] = (double*)malloc(m * sizeof(double));

    for(j = 0; j < m; j++) {
        x[i][j] = rand();
        y[i][j] = rand();
    }
    printf("\n");

  }
  printf("\n\n");
}

以上现在可以正常工作了。需要一些解释 x = (double**)malloc(m * sizeof(double*)); 和x[i] = (double*)malloc(m * sizeof(double));

为什么 * for sizeof(double*) in x = (double**)malloc(m * sizeof(double*));

编辑2

void main(){

 int i, j, k, m, n; 
 printf("Enter a number as the size of two square matrices\n");
 scanf("%d", &m);

 double (*x)[m] = malloc(sizeof(double[m][m]));
 double (*y)[m] = malloc(sizeof(double[m][m]));
 /* initialize random seed: */
 srand(time(NULL));
 for(i = 0; i < m; i++) {
    for(j = 0; j < m; j++) {
        x[i][j] = rand();
        y[i][j] = rand();
    }
    printf("\n");

  }
  printf("\n\n");
}

根据 Jens Gustedt 矩阵分配的变化...我已删除

 double **x;
 double **y;
 x = (double**)malloc(m * sizeof(double*)); 
 y = (double**)malloc(m * sizeof(double*));
 x[i] = (double*)malloc(m * sizeof(double));
 y[i] = (double*)malloc(m * sizeof(double));

Answer 1

这些只是假矩阵，这项技术属于博物馆。在现代 C 语言中，从 C99 开始，只需将 2D 矩阵分配为 double (*matrix)[m] = malloc(sizeof(double[m][m])); 。因此您只需调用 malloc 一次即可整个矩阵并将其全部存储在连续的内存中。
– 延斯·古斯特