Question

我正在为一个应该是双向链表的类编写程序。它编译，但当我尝试执行命令addleft或addright时，我得到一个分段错误错误。我对C ++很新，所以任何建议都会很棒。我发布了代码的相关部分。

列表头文件：

//list.h

#include <string>
using namespace std;

class List {
    friend class Node;
public:
    List();
    void addleft(int);
    void addright(int);
    int left();
    int right();
    void print();
    bool search(int);
    //Node *head;
    //Node *tail;
    //Node *n;
};

列出类文件：

#include <iostream>
#include <string>
#include <stdio.h>
#include "List.h"
#include "Node.h"
using namespace std;
Node *current;
Node *tail;
Node *head;
Node *n;

List::List() {

}

void List::addleft(int a) {
    n = new Node;                                                       //The pointer n points to a new Node
    n->number = a;                                                      //Set the value in the node
    n->next = head;                                                     //Point the node to the old head of the linked list
    head->prev = n;                                                     //Link the old head node to the new node
    head = n;                                                           //Set the new node as the new head of the linked list
    head->prev = NULL;                                                  //Make the new node's previous pointer point to nothing (NULL)
    if(current == NULL) {                                               //If the list is empty...
            current = n;                                                //Set the new node as the current node pointer
        }
}

void List::addright(int a) {
    n = new Node;                                                       //The pointer n points to a new Node
    n->number = a;                                                      //Set the value in the node
    n->prev = tail;                                                     //Point the node to the old head of the linked list
    tail->next = n;                                                     //Link the old tail node to the new node
    tail = n;                                                           //Set the new node as the new tail of the linked list
    tail->next = NULL;                                                  //Make the new node's next pointer point to nothing (NULL)
    if(current == NULL) {                                               //If the list is empty...
        current = n;                                                    //Set the new node as the current node pointer
    }
}

int List::left() {
    current = current->prev;
    return current->number;
}

int List::right() {
    current = current->next;
    return current->number;
}

void List::print() {

}

bool List::search(int a) {
    int search;
    //while(search != tail) {

    //}
}

节点头文件：

//node.h

using namespace std;

class Node {
    friend class List;
public:
    Node();
private:
    int number;
    Node *next;
    Node *prev;
};

节点类文件：

#include <iostream>
#include <string>
#include <stdio.h>
#include "List.h"
#include "Node.h"
using namespace std;

Node::Node() {
    next = NULL;
    prev = NULL;
}

Answer 1

我猜测head和tail最初初始化为空指针。这就是为什么第一次尝试添加任何崩溃的原因。如果是这种情况，您必须通过代码的特殊分支处理第一次添加。当head和tail都为空时，必须专门针对这种情况编写该特殊分支。

编辑：在看到更多代码后，我们可以得出结论，您的代码确实如此。

然而，编写List类然后将head和tail声明为文件范围变量（而不是使它们成为List类的成员）毫无意义。看起来你最初宣称它们是类成员，但后来评论了这些成员。为什么???

为什么这是一个分段错误？

1 个答案: