实例化时的分段错误

Question

我目前正在使用链接列表数据结构。 该列表具有一个指向头节点的指针和一个指向尾节点的指针。

节点类为follode

template<class Type> class Node
{
private:
    Type* storedVertex;
    Node<Type>* next;

public:
    Node()
    {
        storedVertex = NULL;
        next = NULL;
    }

    Node(Type &vertex): next(NULL)
    {
        storedVertex = &vertex;
    }

    Type* get_Vertex()
    {
        return storedVertex;
    }

    Node<Type>* get_Next()
    {
        return this->next;
    }

    void set_Next(Node<Type>* _node)
    {
        this->next = _node;
    }

};

LinkList类：

template<class Type> class LinkList
{
private:
    int sz; //number of entries in linked list.
    Node<Type> *head = NULL;
    Node<Type> *tail = NULL;

public:
    LinkList(): sz(0)
    {
        //O(1)
    }

    ~LinkList()
    {}

    void del_All()
    {
        while (head != NULL)
        {
            Node<Type>* tmp = head;
            head = head->next;
            delete tmp;
        }
        sz = 0;
        tail = NULL;
    }
// /*
    void push_Front(Type _vertex)
    {
        Node<Type>* _node = new Node<Type>(_vertex);
        if(head == NULL)
        {
            head = _node;
            tail = _node;
            sz++;
        }
        else
        {
            _node->next = head;
            head = _node;
            sz++;
        }
    }

    void add_node(Type _vertex)
    {
        Node<Type>* _node = new Node<Type>(_vertex);
        //Adds node to the back of the linkList.
        if (head == NULL)
        {
            //cout << "ptr" << ptr->getNext() << endl;
            head = _node;
            tail = _node;
            sz++;
        }
        else
        {
            Node<Type>* ptr = head;
            while(ptr->get_Next() != NULL)
            {
                ptr = ptr->get_Next();
            }
            ptr->set_Next(_node);
            this->tail = _node;
            sz++;
        }
        //LinkList::printList();
    }
bool is_Empty()
    {
        if(head==0) cout << "Empty" << endl;
        return head==0;
    }

    Node<Type>* get_Head()
    {
        cout << "DEBUG:: IN GET HEAD" << endl;
        if(head == NULL) return NULL;
        return head;
    }

    void set_Head(Node<Type> _Node)
    {
        push_Front(_Node);
    }

    Type get_Tail()
    {
        if(tail == NULL) return NULL;
        return tail;
    }

//Accessors
    int size()
    {
        return sz;
    }

    bool search_for(string data)
    {
        cout << "DEBUG 3" << endl;
        if(this->get_Head() == NULL)
        {
            cout << "DEBUG 3.5" << endl;
            return false;
        }
        else
        {
            cout << "DEBUG 4" << endl;
            Node<Type>* ptr = head;
            if(ptr = NULL) return false;
            cout << "DEBUG AGAIN" << endl;

            cout << "search_for() while loop was ";
            while(ptr != NULL)
            {
                if(ptr->get_Vertex()->get_Data() == data)
                {
                    cout << "not skipped" << endl;
                    return true;
                }
                ptr = ptr->get_Next();
                cout << "not ";
            }
            cout << "skipped.";

            return false;
        }
    }
};

主要：

#include <iostream>
#include <string>
#include "Vertex.h"
#include "HashTable.h"

using namespace std;
int main()
{
            LinkList<string> list;
            cout << "*****Insert*****" << endl;
            cout << "Data(string) to insert: ";
            string data;
            cin >> data;

            Vertex<string>* vertex = new Vertex<string>(data);

            bool insert;
            insert = list.add_node(vertex);
            return 0;
}

这些文件正在我的终端上编译。 当我运行add_Node函数时，它将一直运行直到遇到任何类似（head == NULL）的语句。 这是即时通讯出现段错误的地方。 我不明白这是因为我将头初始化为NULL吗？

Answer 1

我唯一看到的错误是：

  if(ptr = NULL) return false;