pointer was nullptr C 编程错误

Question

我有一个严重的问题。

在第 **c = (int*)malloc(size1 * sizeof(int*)); 行编译器给我这个错误，我真的不知道它说了什么。

Unhandled exception thrown: read access violation.
c was nullptr. occurred

我不知道我做错了什么.. 我像这样初始化每个指针。

void BuildMatrix(int ***, int, int);
void FreeMatrix(int ***, int);
void PrintMatrix(int **, int, int);
int **MultiplyMatrixes(int **, int**, int, int, int);

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 second?[size2, size3]: ");
    scanf("%d %d", &size2, &size3);  /*size2 = rows of matrix2.*/

    /*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] = (int *)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 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++) {

        for (j = 0; j < size3; j++) {
            c[i] = (int *)malloc(size3 * sizeof(int));
            if (c[i] == NULL) {
                printf("*Not enough RAM.\nTerminating.\n");
                FreeMatrix(&c, size1);
                exit(1);
            }
            for (k = 0; k < size2; k++) {
                c[i][j] += (a[i][k] * b[k][j]);
            }
        }
    }
    return c;
}

Answer 1

(*pMat)[i] = (int *)malloc(col * sizeof(int*));

将会

(*pMat)[i] = malloc(col * sizeof(int));

您已在阅读 int-s 的地方为 col 篇 int* 篇分配了 space。

还有

**c = (int*)malloc(size1 * sizeof(int*));

将会

c = malloc(size1 * sizeof(int*));

否则你试图取消引用 NULL 值，这 触发了你得到的错误。

循环也会

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]);
        }
    }
}

不要转换 malloc 的 return 值。

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