试图理解我的代码中的问题

Question

我正在尝试执行以下功能：

•从用户接收3个整数：size1，size2，size3。

•创建一个size1 * size2矩阵和一个size2 * size3矩阵。

•将2个矩阵相乘。

•打印结果矩阵。

•释放所有动态内存。

在输入两个矩阵之后，

BUT我希望程序显示矩阵的乘法，但它会在FreeMatrix函数中导致断点，并这样写：在Project8.exe中的0x0F82AC1D（ucrtbased.dll）处引发异常：0xC0000005：访问冲突读取位置0xCCCCCCC4。

代码：

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

void BuildMatrix(int*** pMat, int row, int col);
void FreeMatrix(int*** matrix, int row);
void PrintMatrix(int** pMat, int row, int col);
int** MultiplyMatrixes(int** a, int** b, int size1, int size2, int size3);

int main() {
    int** matrix1 = NULL, ** matrix2 = NULL, ** matrix3 = NULL;
    int* newCol = NULL;
    int size1, size2, size3, newRow;

    printf("-How many rows in the first matrix?: ");
    scanf("%d", &size1);
    printf("-How many columns in the first matrix and rows in the second matrix?[size2, size3]: ");
    scanf("%d", &size2);  /*size2 = rows of matrix2.*/
    printf("-How many columns in the second matrix?: ");
    scanf("%d", &size3);

    /*Build both matrices*/
    printf("-First matrix input.\n");
    BuildMatrix(&matrix1, size1, size2);
    PrintMatrix(matrix1, size1, size2);
    printf("-Second matrix input.\n");
    BuildMatrix(&matrix2, size2, size3);
    PrintMatrix(matrix2, size2, size3);

    /*Combine the 2 matrices to a new matrix*/
    matrix3 = MultiplyMatrixes(matrix1, matrix2, size1, size2, size3);
    FreeMatrix(&matrix2, size2); //Free the second matrix

    printf("\n-Multiplied matrix: \n");
    PrintMatrix(matrix3, size1, size3);

    FreeMatrix(&matrix3, size1);
    FreeMatrix(&matrix1, size1);
}

void BuildMatrix(int*** pMat, int row, int col) 
{
    int i, j;
    (*pMat) = (int**)malloc(row * sizeof(int*));
    if (*pMat == NULL) 
    {
        free(pMat);
        printf("*Not enough RAM.\nTerminating.\n");
        exit(1);
    }

    for (i = 0; i < row; i++) 
    {
        (*pMat)[i] = malloc(col * sizeof(int));
        if ((*pMat)[i] == NULL) {
            printf("*Not enough RAM.\nTerminating.\n");
            FreeMatrix(pMat, row);
            exit(1);
        }
        for (j = 0; j < col; j++) {
            printf("-Enter %d element in %d row: ", j + 1, i + 1);
            scanf("%d", &(*pMat)[i][j]);
        }
        printf("\n");
    }
    //FreeMatrix(pMat, row);
}

void FreeMatrix(int*** matrix, int row)
{
    for (int i = 0; i < row; i++)
    {
        free((matrix)[i]);
    }
    free(matrix);
}

void PrintMatrix(int** pMat, int row, int col) 
{
    for (int i = 0; i < row; ++i) 
    {
        for (int j = 0; j < col; ++j) 
        {
            printf("%d ", (pMat[i][j]));
        }
        printf("\n");
    }
}

int** MultiplyMatrixes(int** a, int** b, int size1, int size2, int size3)
{
    int i, j, k, ** c = NULL;
    c = (int**)malloc(size1 * sizeof(int*));
    if (c == NULL) 
    {
        free(*c);
        printf("*Not enough RAM.\nTerminating.\n");
        exit(1);
    }

    for (i = 0; i < size1; i++) {
        c[i] = malloc(size3 * sizeof(int));
        if (c[i] == NULL) 
        {
            printf("*Not enough RAM.\nTerminating.\n");
            FreeMatrix(&c, size1);
            exit(1);
        }

        for (j = 0; j < size3; j++) 
        {
            c[i][j] = 0;
            for (k = 0; k < size2; k++) 
            {
                c[i][j] += (a[i][k] * b[k][j]);
            }
        }
    }
}

Answer 1

当您为BuildMatrix中的矩阵分配时：

(*pMat) = (int**)malloc(row * sizeof(int*));

for (i = 0; i < row; i++) 
{
    (*pMat)[i] = malloc(col * sizeof(int));
    ...
}

因此，在FreeMatrix中，您的代码应更改为：

void FreeMatrix(int*** matrix, int row)
{
    for (int i = 0; i < row; i++)
    {
        free((*matrix)[i]); // using *matrix instead of matrix
    }
    free(*matrix); // using *matrix instead of matrix also
}

Answer 2

此代码中有两个问题。第一个问题，这会在FreeMatrix函数中导致您的异常。您传递了int***，但没有取消引用第一个指针。

void FreeMatrix(int*** matrix, int row)
{
    for (int i = 0; i < row; i++)
    {
        free((matrix)[i]); // Type inside free is `int**`, not `int*`
    }
    free(matrix); // Type inside free is `int***`, not `int**`
}

应该是：

void FreeMatrix(int*** matrix, int row)
{
    for (int i = 0; i < row; i++)
    {
        free((*matrix)[i]); // Type inside free is `int**`, not `int*`
    }
    free(*matrix); // Type inside free is `int***`, not `int**`
}

而且在解决此问题之后，您的代码中的matrix3值也出现问题。您缺少return函数中的MultiplyMatrixes语句，并且未分配matrix3变量。

应该是：

int** MultiplyMatrixes(int** a, int** b, int size1, int size2, int size3)
{
    int i, j, k, ** c = NULL;
    c = (int**)malloc(size1 * sizeof(int*));
    if (c == NULL)
    {
        free(*c);
        printf("*Not enough RAM.\nTerminating.\n");
        exit(1);
    }

    for (i = 0; i < size1; i++) {
        c[i] = malloc(size3 * sizeof(int));
        if (c[i] == NULL)
        {
            printf("*Not enough RAM.\nTerminating.\n");
            FreeMatrix(&c, size1);
            exit(1);
        }

        for (j = 0; j < size3; j++)
        {
            c[i][j] = 0;
            for (k = 0; k < size2; k++)
            {
                c[i][j] += (a[i][k] * b[k][j]);
            }
        }
    }

    return c; // <====
}