双链表删除最后一个C

Question

我正在做一个双链表的实现。我希望链表有一定的长度限制。当列表变长时，删除最后一个节点。我这里有些问题。我想定义尾巴，这样我就不必寻找终点。下面是我正在研究的实现，它将允许长度为4，然后开始删除最后一个节点。

/* Doubly Linked List implementation */
#include<stdio.h>
#include<stdlib.h>
#include<string.h>

struct Node  {
    char command[1024];
    struct Node* next;
    struct Node* prev;
};

struct Node* head; //global pointing to head
struct Node* tail; //global pointing to tail

//Creates a new Node and returns pointer to it. 
struct Node* GetNewNode(char *line) {
    struct Node* newCommand = (struct Node*)malloc(sizeof(struct Node));
        int i = 0;
        while(line[i] != '\0'){
            newCommand->command[i] = line[i];
            i++;
        }
        newCommand->prev = NULL;
    newCommand->next = NULL;
    return newCommand;
}

//Inserts a Node at head of doubly linked list
void InsertAtHead(char *line) {
    struct Node* newCommand = GetNewNode(line);
    if(head == NULL) {
        head = newCommand;
        tail = newCommand;
        return;
    }
    head->prev = newCommand;
    newCommand->next = head; 
    head = newCommand;
}
//Use tail to delete the last node
void deleteLast(){
    struct Node* temp = tail;
    tail = temp->prev;
    free(tail->next);
    tail->next = NULL;
}
//Print in reverse orer
void Print() {
    struct Node* temp = tail;
    while(temp != NULL) {
        printf("%s \n",temp->command);
        temp = temp->prev;
    }
}

int main() {

        int numNodes = 0;
        char line[1024];
        head = NULL; 
        tail = NULL; // empty list. set head/tail as NULL. 
        printf("next node: ");
        while (fgets(line, 1024, stdin)) {
            line[strlen(line)-1] = '\0';
            if(numNodes == 4){
                numNodes -= 1;
                deleteLast();
            }
            InsertAtHead(line);Print();
            numNodes += 1;
            printf("next node: ");
        }
        Print();
}

它似乎在删除最后一个节点，但之后会打印一些奇怪的符号。我猜这是我如何释放的问题，但我想不出来。注意：此代码中的一些代码取自https://gist.github.com/mycodeschool/7429492

Answer 1

你的代码看起来不错，然而，有一个错误，在复制命令到节点：

    while(line[i] != '\0'){
        newCommand->command[i] = line[i];
        i++;
    }

应该是：

    while(line[i] != '\0'){
        newCommand->command[i] = line[i];
        i++;
    }
    newCommand->command[i] = '\0';

（您忘记终止复制的命令。）

还请注意，您必须检查不要超出可用空间，例如：

    while(i<1023 && line[i] != '\0'){
        newCommand->command[i] = line[i];
        i++;
    }
    newCommand->command[i] = '\0';