删除链表中的节点无效?

I am using templates in c++ to create a linked list. I have coded a few functions , but the deletion of node ( either from head/tail ) isnt working properly. It displays an error and terminates. When debugging , the 'this' shown in watch windows contains a head which is null, which i have no idea why. Here is my code:

我在c++中使用模板创建一个链表。我编写了一些函数，但是删除节点(头/尾)不能正常工作。它显示一个错误并终止。当调试时，watch windows中显示的“this”包含一个空头，我不知道这是为什么。这是我的代码:

SLlistSc.h

#ifndef SLlistSc_H
#define SLlistSc_H

#include<iostream>
using namespace std;

template<class T> class SLlist;

template <class T> class snode{
    friend class SLlist<T>;
private:
    T info;
    snode<T> *next;
public:
    inline T getter() const { return info; }
    inline void setter(T setValue){ info = setValue; }
    snode(){ info = 0; next = 0; }
    snode(T inf , snode *nex = 0){ info = inf; next = nex; }
    ~snode(){ delete next; }

};
template <class T> class SLlist{
private:
    snode<T> *head, *tail;
    static int total;
public:
    SLlist(){ head = tail = 0; }

    ~SLlist(){
        snode<T> *p = head;
        while (head != 0){
            head = head->next;
            delete p;
            p = head;
        }
    }
    inline void incrcnt(){ total++; }
    inline void decrcnt(){ total--; }
    void displayList();
    void addToHead(T inf);
    void addToTail(T inf);
    T deleteFromHead();
    T deleteFromTail();
    int returnIndex();
    void deleteInfo();
    void deleteAll();
};

template <class T> void SLlist<T>::displayList(){
    snode<T> *p = head;
    while (p != 0){
        cout << "\n->" << p->info;
        p = p->next;
    }
    return;
}

template <class T> void SLlist<T>::addToHead(T inf){
    snode<T> *temp = new snode<T>(inf, 0);
    if (head == 0){ head = tail = temp; temp = 0; delete temp; incrcnt(); return; }
    else { temp->next = head; head = temp; temp = 0; delete temp; incrcnt(); return; }
}

template <class T> void SLlist<T>::addToTail(T inf){
    snode<T> *temp = new snode<T>(inf, 0);
    if (head == 0){ head = tail = temp; temp = 0; delete temp; incrcnt(); return; }
    else{ tail->next = temp; tail = temp; temp = 0; delete temp; return; }
}

template <class T> T SLlist<T>::deleteFromHead(){
    if (head == 0){ cout << "\nList is already empty"; return (T)0; }
    if (head == tail){ delete head; head = tail = 0; T info = head->info; return info; }
    else {
        T info = head->info;
        snode<T> *temp = head;
        head = head->next;
        temp = 0;
        delete temp;
        return info;
    }
}

template <class T> T SLlist<T>::deleteFromTail(){
    if (head == 0){ cout << "\nList is already empty"; return (T)0; }
    if (head == tail){ delete head; head = tail = 0; T info = head->info; return info; }
    else {
        T info = tail->info;
        snode<T> *temp = head;
        while (temp != 0)
        {
            temp = tail;
        }
        delete tail;
        tail = temp;
        temp = 0; delete temp;
        return (T)info;
    }
}

#endif

and the cpp file : SLlistSc.cpp

和cpp文件:SLlistSc.cpp。

// SLlistSc.cpp : Defines the entry point for the console application.
//

#include"SLlistSc.h"
#include<iostream>
using namespace std;

template <class T> int SLlist<T>::total = 0;

void main()
{
    cout << "\t\t\t Singly Linked List Super Class Implementation";
    SLlist<int> List1;
    int userchoice=0, inf=0;
    do{
        cout << "\n\n\t\t Menu"
            << "\n\t1. Display List"
            << "\n\t2. Add to Head"
            << "\n\t3. Add to tail"
            << "\n\t4. Delete from Head"
            << "\n\t5. Delete from Tail"
            << "\n\t6. Exit";
        cin >> userchoice;

        switch (userchoice){
        case 1: List1.displayList(); break;
        case 2: cout << "\nEnter info to be added:";
                cin >> inf;
                List1.addToHead(inf); break;
        case 3: cout << "\nEnter info to be added:";
                cin >> inf;
                List1.addToTail(inf); break;
        case 4: inf = List1.deleteFromHead();
                cout << "\n Value" << inf << "deleted from list"; break;
        case 5: inf = List1.deleteFromTail();
                cout << "\n Value" << inf << "deleted from list"; break;
        case 6: cout << "\n\t\t\t\tExiting";
                exit(0);
        default: continue;
        }
    } while (userchoice < 4);
}

Another thing i would like to ask is , when we use templates on a class (eg. class A) , we are required to replace the A with A everywhere. Is it because compiler generates a new class ie.

我想问的另一个问题是，当我们在一个类上使用模板时(如。A类)，我们需要用A来代替A。是因为编译器生成了一个新类ie。

A<T> isnt = A.

< T >不是=。

And while using friend class SLlist inside snode class , why do i have to declare as follows :

在snode类中使用friend类SLlist时，为什么要声明如下:

template<class T> class SLlist;

before the snode class? why cant i declare it directly in the snode class as :

在综述类?为什么我不能直接在snode类中声明它:

friend class SLlist<T>;

Also if there is a chance of improvemet in my code , please go hard on me. Thanks.

如果我的代码有改进的机会，请对我严厉一点。谢谢。

1 个解决方案

#1

You are attempting to use a pointer that is invalid because the block containing that pointer has been freed.

您正在尝试使用一个无效的指针，因为包含该指针的块已被释放。

The Microsoft C++ debug runtime library overwrites freed memory with the pattern 0xFEEEFEEE which makes this problem easier to identify.

Microsoft c++调试运行时库覆盖了释放内存和模式0xFEEEFEEE，这使得这个问题更容易识别。

#1