C struct错误"不允许指向不完整类类型的指针"

Question

我正在使用Visual Studio 2013 Professional,我也在Kali和Ubuntu的Eclipse中尝试过它.

有更多区域出现相同的两个错误,但我只会在这里显示一些代码.

我已经看到了一些与同一问题相关的问题.大多数答案似乎是结构先前没有定义,虽然我不认为这适用于此.我还尝试将所有代码放入单个源文件中,这没有任何改变.

Visual Studio强调了代码显示中的错误,error: pointer to incomplete class type is not allowed当我构建项目时,它显示error C2037: left of 'previous' specifies undefined struct/union 'NODE'这些位置在下面的代码中注明.

另一个错误是warning C4133: '=' : incompatible types - from 'NODE *' to 'NODE *',下面也提到了位置.

所以当然我的问题是如何解决这些错误？

我头文件中的相关信息:

list.h
    #ifndef LIST_H
    #define LIST_H

    typedef struct node{
        struct NODE *next;
        struct NODE *previous;
    }NODE;

    typedef struct list{
        NODE node;
        int count;
    }LIST;

    extern void     listDelete(LIST *pList, NODE *pNode);
    extern void     listFree(LIST *pList);
    #endif

我的C源文件中的相关信息:

list.c
    #include "list.h"
    #define HEAD    node.next       /* first node in list */  
    #define TAIL    node.previous       /* last node in list */  

    void listDelete(LIST *pList, NODE *pNode)
    {
        NODE *mynode;
        if (pNode->previous == NULL)
        {
            pList->HEAD = pNode->next;
        }
        else
        {
            pNode->previous->next = pNode->next; // pointer to incomplete class type is not allowed
        }

        if (pNode->next == NULL)
        {
            pList->TAIL = pNode->previous;
        }
        else
        {
            pNode->next->previous = pNode->previous; // pointer to incomplete class type is not allowed
        }

        pList->count--;
    }

    void listFree(LIST *pList)
    {
        NODE *p1, *p2;

        if (pList->count > 0)
        {
            p1 = pList->HEAD; // warning C4133: '=' : incompatible types - from 'NODE *' to 'NODE *'
            while (p1 != NULL)
            {
                p2 = p1->next; // warning C4133: '=' : incompatible types - from 'NODE *' to 'NODE *'
                free((char *)p1);
                p1 = p2;
            }
            pList->count = 0;
            pList->HEAD = pList->TAIL = NULL;
        }
    }

Answer 1

你不能NODE在里面定义使用struct node,因为NODE还没有定义.

缓慢的做法是:

struct node {
    struct node *next;
    struct node *previous;
};

typedef struct node NODE;

因此,在定义了什么之后struct node,您可以将其称为NODE.

更改

typedef struct node{
    struct NODE *next;
    struct NODE *previous;
}NODE;

至

typedef struct node {
    struct node *next;
    struct node *previous;
} NODE;