Question

我有一个程序可以创建一个已排序的链表，在测试后它可以用来创建列表。尝试删除列表中的元素时出现问题。这些类型是隐藏的，在代码中你会看到参数void* newObj，并且struct有一个用于进行实际比较的函数指针。

我的代码段错误，我相信这是因为列表的负责人没有更新，因此传递价值问题，但我不知道如何修复它。

功能：

int SLRemove(SortedListPtr list, void *newObj)
{
    SortedListPtr temp;
    SortedListPtr temp2;

    if(list->CompareFcn(newObj, list->value) == 0)
    {
        if(list->flag == 1)
        {
            return 0;
        }
        temp = list;
        list = list->next;
        printf("(if)Address of object: %p with value %d, freed.\n", temp, *(int*)temp->value);
        free(temp);
        printf("New head of list is, address: %p, value: %d.\n", list, *(int*)list->value);
        return 1;
    }
    for (temp = list; temp != NULL; temp = temp->next)
    {
        printf("Address of TEMP: %p\n", temp);
        temp2 = temp->next;
        if(temp2->CompareFcn(newObj, temp2->value) == 0)/*value == *newObj*/
        {
            temp->next = temp2->next;
            printf("(loop)Address of object: %p, freed.\n", temp2);
            free(temp2);
            return 1;
        }
    }

    return 0;
}

呼叫者：

for (icount = 1; icount <= 3; icount += 1)
    {
        *ptr[icount-1] = icount;
        printf("Removing...\n");
        printf("Current head of list to be removed, address: %p, value: %d.\n", integerList, *(int*)integerList->value);
        if (SLRemove(integerList, ptr[icount-1]) == 1)
        {
            printf("SLRemove number %d, success!\n\n", icount);
            free(ptr[icount-1]);
        }
        else
        {
            printf("SLRemove number %d failed!\n\n", icount);
        }
    }

Valgrind的：

Removing...
Current head of list to be removed, address: 0x51f1040, value: 1.
Comparing newObj: 1 and item: 1. Returning 0.
(if)Address of object: 0x51f1040 with value 1, freed.
New head of list is, address: 0x51f1140, value: 2.
SLRemove number 1, success!

==23304== Invalid read of size 8
==23304==    at 0x400826: main (main.c:63)
==23304==  Address 0x51f1040 is 0 bytes inside a block of size 32 free'd
==23304==    at 0x4C2A82E: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==23304==    by 0x400B8D: SLRemove (sorted-list.c:176)
==23304==    by 0x400805: main (main.c:60)
==23304==

Answer 1

您正在修改SLRemove（）中的list，但由于它是按值传递的，因此该更改永远不会返回给调用者。试试

int SLRemove(SortedListPtr *list_ptr, void *newObj)
{
  SortedListPtr list = *list_ptr;
  .
  .
  .
    *list_ptr = list;
    return 1;
  .
  .
  .
}

当你打电话时，请使用：

    if (SLRemove(&integerList, ptr[icount-1]) == 1)

C函数具有数据结构指针参数

1 个答案: