C编程-Malloc/Free [英] C Programming- Malloc/Free

问题描述

所以我有一个代码，当我运行它时，当我输入大于3的大小时，它会挂起.当它恰好是3时，它会平稳运行.我将问题缩小为malloc和free，但我不知道问题是什么.我是新来的，因此不胜感激.

So I have a code and when I run it, it hangs when I enter a size greater than 3. When it's exactly 3 it runs smoothly. I narrowed down the problem to malloc and free and I don't know what the problem is. I'm new at this so any help is appreciated.

do  //repeatedly ask the user to put a number between 3-9
{ 
 printf("Enter the size of the game board between 3-9: ");
 scanf("%d", &size);
}while(size<3 || size>9);

if((board = (char***)malloc(sizeof(char**)*size))==NULL)
  printf("Memory Allocation failed\n");
  for(i=0; i<size; i++)
  {
    if((board[i] = (char**)malloc(sizeof(char*)*size))==NULL)
     printf("Memory Allocation failed\n");
     for(j=0; j<size; j++)
     {
       if((board[i][j] = (char *)malloc(sizeof(char)*4))==NULL)  
         printf("Memory Allocation failed\n");
         strcpy(board[i][j], "Go");
     }   
 } 
/*************Some random code ***********/ 

free(board);
for(i=0;i<size;i++)
{
 free(board[i]);
 for(j=0;j<size;j++)
   free(board[i][j]);
}

推荐答案

问题是您在free d之后访问了board.您应该以与malloc完全相反的顺序释放内存.

The problem is you access board after you freed it. You should release memory in exactly the reverse order that you malloc it.

另一种方法是，您可以整体分配所需的所有内存，例如

An alternative approach is that you can allocate all the memory you need in a whole, like

 char ***board = NULL;
 char  **rows  = NULL;
 char   *data  = NULL;

 if((board = (char***)malloc(sizeof(char**)*size))==NULL)
  printf("Memory Allocation failed\n");
 if((rows = (char**)malloc(sizeof(char*)*size*size))==NULL)
     printf("Memory Allocation failed\n");
 if((data = (char *)malloc(sizeof(char)*size*size*4))==NULL)  
     printf("Memory Allocation failed\n");

 for (i = 0; i < size; i++) {
     int board_offset = i * size;
     board[i] = rows[board_offset];
     for (j = 0; j < size; j++) {
         int row_offset = board_offset + j;
         rows[row_offset] = data[row_offset * 4]；
         stcpy(data[row_offset * 4], "GO");
     }
 }

 free(board);
 free(rows);
 free(data);

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