c - 初始化结构的矩阵(双指针)成员

Question

我在指点方面遇到了困难，有人可以帮我一下吗？

我正在尝试在结构数组中初始化一个双(双)指针，但不知何故我做错了。示例:

struct MyStruct
{
    double **matrix;
};

double **CalculateMatrix(...)
{
    double **matrix = (double**)malloc(ROWS * sizeof(double*));
    for (int i = 0; i < ROWS; i++)
        matrix[i] = (double*)malloc(COLS * sizeof(double));
    // + assign some values
    return matrix;
}

void Initialize(struct MyStruct *structs, int size)
{
    for (int i = 0; i < size; i++)
        // Here structs[i].matrix holds the correct matrix values
        structs[i].matrix = CalculateMatrix(...);
}

int main()
{
    struct MyStruct *structs = (struct MyStruct*)malloc(SIZE * sizeof(struct MyStruct));
    Initialize(structs, SIZE);
    // but once the function returns, matrix values are completely different
}

对不起，如果它是重复的，我找不到任何东西

Answer 1

这里不需要全局变量。因此，您可以在 main 方法中声明、定义和初始化结构数组的大小，以及矩阵的维度。

此外，您的方法名称具有误导性，我将它们更改为可以向作者传达每个函数的用途的名称。或者，更准确地说，您的方法执行的任务不止一项。为可重用性划分任务是很好的做法。

这是一个让您入门的最小示例:

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

struct MyStruct
{
    double **matrix;
};

double **allocate_matrix(int rows, int cols)
{
    double **matrix = malloc(rows * sizeof(double*));
    for (int i = 0; i < rows; i++)
        matrix[i] = malloc(cols * sizeof(double));
    return matrix;
}

void allocate_matrices(struct MyStruct *structs, int size, int rows, int cols)
{
    for (int i = 0; i < size; i++)
        structs[i].matrix = allocate_matrix(rows, cols);
}

void fill_matrices(struct MyStruct *structs, int size, int rows, int cols)
{
    for (int i = 0; i < size; i++)
        for(int j = 0; j < rows; j++)
            for(int z = 0; z < cols; z++)
                structs[i].matrix[j][z] = -1.2;
}

void print_matrices(struct MyStruct *structs, int size, int rows, int cols)
{
    for (int i = 0; i < size; i++)
        for(int j = 0; j < rows; j++)
            for(int z = 0; z < cols; z++)
                printf("%f\n", structs[i].matrix[j][z]);
}

void free_matrices(struct MyStruct *structs, int size, int rows) {
    for (int i = 0; i < size; i++) {
        for(int j = 0; j < rows; j++) {
            free(structs[i].matrix[j]);
        }
        free(structs[i].matrix);
    }
}


int main()
{
    int rows = 3, cols = 4, size = 2;
    struct MyStruct *structs = malloc(size * sizeof(struct MyStruct));
    structs[0].matrix = NULL;
    structs[1].matrix = NULL;
    if(structs[0].matrix == NULL)
        printf("null\n");
    allocate_matrices(structs, size, rows, cols);
    if(structs[0].matrix == NULL)
        printf("null\n");
    fill_matrices(structs, size, rows, cols);
    print_matrices(structs, size, rows, cols);
    free_matrices(structs, size, rows);
    free(structs);
}

输出:

null
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000
-1.200000

灵感来 self 的 2D dynamic array (C) .