Question

当尝试在具有两个节点的链表上运行我的deleteLast（）函数两次（获取空列表）时，我遇到了问题。代码编译并运行，但是当我在空链表上调用traverse（）时，我得到一个无限循环，我无法确定原因。

奇怪的是，如果我两次调用deleteFirst（）而不是deleteLast（），程序会正常运行并终止。

以下是我的方法的代码：

#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#include <time.h>

struct NODE
{
    struct NODE *link;
    int value;
};

typedef struct NODE Node;



/* Deletes the first item in the list and returns next item */
Node *deleteFirst(Node **ptrToHeadPtr)
{
    Node *current;

    // If list is empty do nothing
    if (*ptrToHeadPtr == NULL)
        return NULL;

    else
    {
        current = *ptrToHeadPtr;
        *ptrToHeadPtr = current->link;
        free(current);
    }

    return *ptrToHeadPtr;
}

/* Inserts a new Node to the end of the list and returns it */
Node *insertLast(Node **ptrToHeadPtr, int val)
{
    Node *current, *lastNode;
    lastNode = (Node *)malloc( sizeof (Node) );

    // Check if malloc was successful
    if(!lastNode) return NULL;

    lastNode->value = val;
    lastNode->link = NULL;

    if (*ptrToHeadPtr == NULL)
        *ptrToHeadPtr = lastNode;

    else
    {
        current = *ptrToHeadPtr;

        // Walk to the end of the list
        while(current->link != NULL)
            current = current->link;

        // Insert new item at the end of the list
        current->link = lastNode;
    }
    return lastNode;
}

/* Deletes the last Node in the list and returns*/
Node *deleteLast(Node **ptrToHeadPtr)
{
    Node *current, *previous;

    /* If list is empty do nothing */
    if (*ptrToHeadPtr == NULL)
        return NULL;

    current = *ptrToHeadPtr;
    previous = NULL;

    /* If list has one item delete it and return NULL */
    if (current->link == NULL)
    {
        *ptrToHeadPtr == NULL;
        free(current);
        return NULL;
    }
    else
    {
        /* Walk to the end of the list */
        while (current->link != NULL)
        {
            previous = current;
            current = current->link;
        }

        previous->link = NULL;
        free(current);
        return previous;
    }       
}


/* Traverses the list, printing the value of each Node */
void traverse(Node*p)
{
    while( p!= NULL )
    {
        printf("%d ",p->value);
        p=p ->  link;
    }
}

/* Walks through the linked list, freeing memory of each Node */
void freeList(Node *p)
{
    Node *temp;
    while( p != NULL )
    {
        temp = p;
        p = p-> link;
        free(temp);
    }
}


int main()
{
    Node *headPtr = NULL;

    insertLast( &headPtr, 33 );
    insertLast( &headPtr, 35 );

    traverse(headPtr);
    printf("\n");

    deleteFirst ( &headPtr );
    traverse(headPtr);
    printf("\n");

    deleteLast ( &headPtr );

    traverse(headPtr);
    freeList(headPtr);
    return 1;
}

Answer 1

在你的deleteLast（）函数中（他们在C中调用函数，只是你知道，而不是方法。不要试图听起来很讽刺。）

    /* If list has one item delete it and return NULL */
if (current->link == NULL)
{
    *ptrToHeadPtr == NULL; // CHANGE THIS TO =, NOT ==
    free(current);
    return NULL;
}

编辑：就像上面提到的海报一样，你应该用-Wall编译（W是区分大小写的，必须大写。）它会抓住这个。

ANSI C S-Linked List - deleteLast（）无法正常运行

1 个答案: