Question

没有重新分配内存到'转置'我尝试重新分配'矩阵'https://codepad.remoteinterview.io/WGIBSKENXV当我在网上运行它它工作正常但在visual basic 2017上，它给了我访问冲突错误在双循环部分。刚刚为“转置”分配新内存的方式在网络上也可以正常工作，但在visual basic 2017上它会出现访问冲突错误。有什么不对？

当我在定义的函数中分配内存时，我应该在main函数中释放它吗？和'矩阵'（我在main函数中分配的那个）一样？我做得对吗？

 # 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, i;
 int **matrix;

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

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

 srand(2016);
 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);

         i = 0;
 while(matrix[i] != 0){
        free(matrix[i]);
        ++i;
 }
    free(matrix);
  /*
    i = 0;
    while(transposed[i] != 0){
         free(transposed[i]);
         ++i;
    }
    free(transposed);
  */   
    return 0;
 }
       //When I allocate memory in a defined function, should I free it in the main function? as with 'matrix'? Did I do it correctly?

 int** transpose (int **matrix, int rows, int cols){

 int i ,j;

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

   for (i = 0; i < rows; i++) {
    for (j = i +1 ; j < cols ; j++) {
     tmp= *(*(matrix + i) + j);
     *(*(matrix + i) + j) = *(*(matrix + j) + i);
     *(*(matrix + j) + i) = tmp;
    }
 }
      return matrix;

 // Without newly allocating memory to 'transposed' I tried to realloc on 'matrix'
 https://codepad.remoteinterview.io/WGIBSKENXV when I run it on web it works fine but on visual basic 2017, it gives me access violation error at double for loop part.


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

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

 // Just allocating new memory to 'transposed' works okay on web https://codepad.remoteinterview.io/WGIBSKENXV, but on visual basic 2017 it gives access violation error. When I allocate memory in a defined function, should I free it in the main function? as with 'matrix'? Did I do it correctly?
 }     
 void printMatrix(int **matrix, int m, int n){
 int i, j;

 for( i = 0; i < m; i++ ){
 for( j = 0; j < n; j++ ){
 printf("%4d", *(*(matrix + i )+j) );
 }
 printf("\n");
 }

 }

Answer 1

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

在这种情况下，您将使用较小的行重新分配矩阵，但是后面的循环仍会访问它，直到rows

   for (i = 0; i < rows; i++) {
    for (j = i +1 ; j < cols ; j++) {
     tmp= *(*(matrix + i) + j);
     *(*(matrix + i) + j) = *(*(matrix + j) + i);
     *(*(matrix + j) + i) = tmp;
    }
 }

*(*(matrix + i) + j);当我＆gt; cols将导致访问无效内存，因为矩阵被重新分配到cols个地址

使用c指针转置矩阵，内存访问错误

1 个答案: