Question

以下是List ADT，

typedef struct List{
  void **array;

  /* Following members for Housekeeping - Array enhancement*/
  int lastItemPosition;
  int size;
}List;
#define INITIAL_LIST_SIZE 50

createList操作会尝试free(*(list->array))期望释放void*数组，但不会释放指向每个void*的对象，因为listPointer采用浅层副本list

List *createList(List *list, Op opType){

  List *listPointer = (List *)malloc(sizeof(List));
  void *accumulator = NULL;
  if(opType == CREATE_NEW_LIST){

    accumulator = malloc(INITIAL_LIST_SIZE*sizeof(void*));
    listPointer->array = &accumulator;

    /* Is it safe to initialise zero to  element of array of void* pointers? */
    listPointer->array = memset(listPointer->array, 0, INITIAL_LIST_SIZE*sizeof(void *));

    listPointer->lastItemPosition = -1;
    listPointer->size = INITIAL_LIST_SIZE;
  }else if(opType == DOUBLE_THE_LIST){

    accumulator = malloc(2*(list->size)*sizeof(void *));
    listPointer->array = &accumulator;

    /* Performing shallow copy, Is deep copy required? */
    listPointer->array = memcpy(listPointer->array, list->array, list->size*sizeof(void*));

    listPointer->lastItemPosition = list->lastItemPosition;;
    listPointer->size = 2*(list->size);

    free(*(list->array)); // How to free  list pointer and its members?

  }else if(opType == HALF_THE_LIST){

    accumulator = malloc(((list->size)/2)*sizeof(void *));
    listPointer->array = &accumulator;

    /* Performing shallow copy, Is deep copy required? */
    listPointer->array = memcpy(listPointer->array, list->array, (list->size/2)*sizeof(void *));
    listPointer->lastItemPosition = list->lastItemPosition;
    listPointer->size = (list->size)/2;

    free(*(list->array)); // How to free  list pointer and its members?
  }

  return listPointer;

}

执行以下列表操作List，

void insertItem(List *, void *newItem);
void deleteItem(List *, int listIndex);

用户访问，

/* main.c */

#include"list.h"

int main(void){
  List *arrayList = createList((List *)NULL, CREATE_NEW_LIST);


  if (arrayList == (List *)NULL){
    fprintf(stderr, "Unable to createList() \n");
    exit(1); //Nothing else to do without arrayList
  }

  /* Objects should be on heap */
  int *object = malloc(sizeof(int));

  *object = 650;


  insertItem(arrayList, object);
}

问题：

请您澄清一下，我的代码中free（*（list-＆gt; array））的作用是什么？

Answer 1

以下代码剪辑应该完成这项工作：

else if(opType == DOUBLE_THE_LIST){

    listPointer->array = realloc(listPointer->array, 2*(list->size)*sizeof(void *));

    listPointer->lastItemPosition = list->lastItemPosition;;
    listPointer->size = 2*(list->size);

    // do not free any more: free(*(list->array)); // How to free  list pointer and its members?
}

Answer 2

对于选项DOUBLE_THE_LIST和选项HALF_THE_LIST，您的代码将使用现有list进行调用。

然后代码创建一个新列表，并将现有列表的全部或一半复制到新列表中。

然后使用free(*(list->array));

删除现有列表（也称为免费）

最后，使用return listPointer;

返回新列表

因此，在使用带有这些选项的函数时，应始终将返回值分配给与用作参数的列表相同的列表。那就是：

myList = createList(myList, HALF_THE_LIST);

如果你这样做：

myListB = createList(myListA, HALF_THE_LIST);

你myListA指向已经免费的内存，这是不好的。

List ADT - 如何释放结构指针及其成员？

2 个答案: