c - 在C中动态分配二维数组的总和

Question

对于这个练习(我们必须扫描 txt 文件并返回行、列、矩阵 1 和矩阵 2；然后求矩阵 1 和 2 的和)，“使用动态内存分配”有额外的学分，即前面几章。鉴于下面的程序，我将如何去做呢？我知道动态内存分配的4个函数(malloc、calloc、free和realloc)，但还不知道如何使用它们。

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main()
{
    FILE *inFile;
    int i,j;
    int rows, cols;

    inFile = fopen ("Matrix.txt", "r");

    if (inFile == NULL)
    {
        printf("\n\nFile does not exist or cannot be opened.\n");
        exit(1);
    }
    fscanf(inFile,"%d %d", &rows, &cols);

    int m1[rows][cols],m2[rows][cols],m3[rows][cols];

    /*Scan and store Matrix 1 and Matrix 2*/
    for (i = 0; i < rows; i++) 
    {
        for ( j = 0;j<cols;j++)
        {
            fscanf(inFile,"%d", &m1[i][j]);
        }
    }
    for (i = 0; i < rows; i++) 
    {
        for ( j = 0;j<cols;j++)
        {
            fscanf(inFile,"%d", &m2[i][j]);
        }
    }

    fclose(inFile);

    printf("\nThe sum of the two matrices:\n");
    for (i = 0; i < rows; i++)
    {
        for (j = 0; j < cols; j++)
        {
            m3[i][j]=m1[i][j]+m2[i][j];
            printf("    %d", m3[i][j]);
        }
        printf("\n");
    }

}

Answer 1

我没有您的“Matrix.txt”文件，因此我无法调试我编写的代码，但无论如何它都在这里。

两个答案合二为一。惰性方式和二维数组方式。 在大多数情况下，我倾向于将 2D 数组作为 1D 数组来处理，因为它的代码更少，需要跟踪的东西也更少。

为了测试它，只需注释或取消注释#define。

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

#define IF_LAZY (1) // comment/uncomment this line if you like lazy solutions or not.

int main() {
    FILE *inFile;
    int i, j;
    int rows, cols;

    inFile = fopen("Matrix.txt", "r");

    if (inFile == NULL) {
        printf("\n\nFile does not exist or cannot be opened.\n");
        exit(1);
    }
    fscanf(inFile, "%d %d", &rows, &cols);

#ifdef IF_LAZY

    /* Dynamic allocation using 1D arrays. */
    int* m1 = (int*) malloc(sizeof(int) * rows * cols);
    int* m2 = (int*) malloc(sizeof(int) * rows * cols);
    int* m3 = (int*) malloc(sizeof(int) * rows * cols);

#else

    /* Dynamic allocation using 2D arrays made out of pointers to pointers. */
    int** m1 = (int**) malloc(sizeof(int*) * rows);
    for(int i = 0; i < rows; i++) {
        m1[i] = (int*) malloc(sizeof(int) * cols);
    }

    int** m2 = (int**) malloc(sizeof(int*) * rows);
    for(int i = 0; i < rows; i++) {
        m2[i] = (int*) malloc(sizeof(int) * cols);
    }

    int** m3 = (int**) malloc(sizeof(int*) * rows);
    for(int i = 0; i < rows; i++) {
        m3[i] = (int*) malloc(sizeof(int) * cols);
    }

#endif

#ifdef IF_LAZY

    /*Scan and store Matrix 1 and Matrix 2*/
    for (i = 0; i < rows; i++) {
        for (j = 0; j < cols; j++) {
            fscanf(inFile, "%d", &m1[i * cols + j]);
        }
    }
    for (i = 0; i < rows; i++) {
        for (j = 0; j < cols; j++) {
            fscanf(inFile, "%d", &m2[i * cols + j]);
        }
    }

    fclose(inFile);

    printf("\nThe sum of the two matrices:\n");
    for (i = 0; i < rows; i++) {
        for (j = 0; j < cols; j++) {
            m3[i * cols + j] = m1[i * cols + j] + m2[i * cols + j];
            printf("    %d", m3[i * cols + j]);
        }
        printf("\n");
    }

#else
    /*Scan and store Matrix 1 and Matrix 2*/
    for (i = 0; i < rows; i++) {
        for (j = 0; j < cols; j++) {
            fscanf(inFile, "%d", &m1[i][j]);
        }
    }
    for (i = 0; i < rows; i++) {
        for (j = 0; j < cols; j++) {
            fscanf(inFile, "%d", &m2[i][j]);
        }
    }

    fclose(inFile);

    printf("\nThe sum of the two matrices:\n");
    for (i = 0; i < rows; i++) {
        for (j = 0; j < cols; j++) {
            m3[i][j] = m1[i][j] + m2[i][j];
            printf("    %d", m3[i][j]);
        }
        printf("\n");
    }
#endif

}