Question

我正在尝试编写一个使用指针和内存分配来转置矩阵的代码。

当我运行它时，它会冻结在下面给出的程序中产生 rand function 矩阵的部分。

所以我无法检查两个函数（transpose，printMatrix）是否有效。

我做错了什么？

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

int** transpose (int **matrix, int m, int n);
void printMatrix(int **matrix, int m, int n);

int main (void){
    int rows, cols;
    int r, c;
    int **matrix;

    printf("Number of Rows : ");
    scanf("%d", &rows);
    printf("Number of Cols : ");
    scanf("%d", &cols);

    matrix = (int **)malloc(rows*sizeof(int*));
    matrix[0] = malloc(rows*cols*sizeof(int));

    srand(2016);

 //error starts from here
    for( r = 0; r < rows; r++ ){
        for( c = 0; c < cols; c++ ){
            *(*(matrix + r)+c) = rand() % 99 + 1;
        }
    }

    printf("Matrix produced with seed number 2016\n");
    printMatrix(**matrix, rows, cols);

    matrix = transpose(**matrix, rows, cols);

    printf("Transposed Matrix\n");
    printMatrix(**matrix, rows, cols);              
}

int** transpose (int **matrix, int rows, int cols){
    int tmp, i ,j;

    if( rows < cols ){
        matrix[0] = (int *)realloc(matrix[0], rows*rows*sizeof(int));
    }
    else if(cols < rows){
        matrix = (int **)realloc(matrix, cols*sizeof(int*));
    }

    for (i = 0; i < rows; i++) {
        for (j = 0 ; j < cols; j++) {
            tmp = *(*(matrix + i) + j);
            *(*(matrix + i) + j) = *(*(matrix + j) + i);
            *(*(matrix + j) + i) = tmp;
        }
    }  
    return matrix;
}
void printMatrix(int **matrix, int m, int n){
    int i, j;

    for( i = 0; i < m; i++ ){
        for( j = 0; j < n; j++ ){
            printf("%3d", *(*(matrix + i )+j) );
        }
        printf("\n");
    }

}

Answer 1

您正在从matrix [0]开始分配连续的行数* cols * sizeof（int）：

matrix[0] = malloc(rows*cols*sizeof(int));

我认为分配应该是：

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

Answer 2

您的问题在于以下代码：

matrix = (int **)malloc(rows*sizeof(int*));
matrix[0] = malloc(rows*cols*sizeof(int));

在第一个语句中，您尝试分配指针数组。但是，在第二个语句中，您只将内存分配给一个指针。因此，当您尝试执行*(*(matrix + r)+c)时，它会访问无效的内存。

你应该这样做：

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

Answer 3

正如其他答案所述，您的问题在于矩阵的内存分配。但是你的问题并没有就此止步。当你想在函数中使用双指针时，你也传递了矩阵的值。

请参阅更正后的代码：

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

int** transpose (int **matrix, int m, int n);
void printMatrix(int **matrix, int m, int n);

int main (void){
    int rows, cols;
    int r, c;
    int **matrix;

    printf("Number of Rows : ");
    scanf("%d", &rows);
    printf("Number of Cols : ");
    scanf("%d", &cols);

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

    srand(2016);

 //error starts from here
    for( r = 0; r < rows; r++ ){
        for( c = 0; c < cols; c++ ){
            *(*(matrix + r)+c) = rand() % 99 + 1;
        }
    }

    printf("Matrix produced with seed number 2016\n");
    //Changed this, you where doing printMatrix(**matrix, rows, cols);
    printMatrix(matrix, rows, cols);

    //Changed this, you where doing matrix = transpose(**matrix, rows, cols);
    matrix = transpose(matrix, rows, cols);

    printf("Transposed Matrix\n");
    //Changed this, you where doing printMatrix(**matrix, rows, cols);
    printMatrix(matrix, rows, cols);              
}

int** transpose (int **matrix, int rows, int cols){
    int tmp, i ,j;

    if( rows < cols ){
        matrix[0] = (int *)realloc(matrix[0], rows*rows*sizeof(int));
    }
    else if(cols < rows){
        matrix = (int **)realloc(matrix, cols*sizeof(int*));
    }

    for (i = 0; i < rows; i++) {
        for (j = 0 ; j < cols; j++) {
            tmp = *(*(matrix + i) + j);
            *(*(matrix + i) + j) = *(*(matrix + j) + i);
            *(*(matrix + j) + i) = tmp;
        }
    }  

}
void printMatrix(int **matrix, int m, int n){
    int i, j;
    for( i = 0; i < m; i++ ){
        for( j = 0; j < n; j++ ){
            printf("%3d", *(*(matrix + i )+j) );
        }
        printf("\n");
    }

}

使用指针C转置矩阵

3 个答案: