Программа с двусвязным списком крашится - C++ - Ответ 5474143

#include <iostream>
#include "stdlib.h"
#include <fstream>
 
using namespace std;
 
template <class T>
 
struct listitem
{
    T value;
    listitem <T> *next, *prev;
};
 
//static listitem base;
//static listitem *current;
//static listitem numofelem;
 
 
template <class T>
class list2
{
private:
    listitem <T> base;
    listitem <T> *current;
 
    int numofelem;
public:
    void createlist2();
 
 
 
    ~list2(); //destructor
 
    //void printlist(const int i);
    void printlistleft2right();
    void printlistright2left();
    void clearlist();
    void copylist(const list2 <T> &a);
 
    int gonext();
    int goprev();
    void gobeg ();
    void goend ();
 
    void addbefore(T x);
    void addafter(T x);
 
    //bool deletebefore();
    //bool deleteafter();
    void delcurrent();
/*
    bool getbefore(T &x);
    bool getafter (T &x);*/
 
    int numelem();
    //void deleteafter();
    //void deletebefore();
 
    bool isempty();
    bool atbeg();
    bool atend();
 
    /*T &ValBefore();
    T &ValAfter ();*/
 
    T &currentval();
 
    list2 <T> &operator=(const list2 <T> &a)
    {
        clearlist();
        copylist(a);
        return *this;
    }
};
 
template <class T>
void list2 <T>::createlist2()
{
   current=&base;
   base.next=base.prev=&base;
   numofelem=0;
}
 
template <class T>
void list2 <T>::copylist(const list2 <T> &a)
{
    listitem <T> *current;
 
    current = a.base.next;
    gobeg();
 
    while( !(current == &a.base) )
    {
        addbefore(current -> value);
        current = current -> next;
    }
 
    current = a.base.next -> prev;
    gobeg();
 
    while( !(current == a->prev) )
    {
        gonext();
        current = current -> next;
    }
}
 
template <class T>
void list2 <T>::clearlist()
{
    gobeg();
    while(!atend()) delcurrent();
}
 
/*template <class T>
void list2 <T>::PrintList(const int i)
{
        list2Item <T> *s = &base;
        s = s -> next;
 
        cout << "[ ";
        if( ( (s == &base) || (AtBeg()) ) && (i != 0) ) cout << "^ ";
        while(s != &base)
        {
            cout << s -> value << " ";
            if( (s == before) && (i != 0) ) cout << "^ ";
            s = s -> next;
        }
        cout << "]" << endl;
        return;
}
*/
 
/*template <class T>
list2 <T>::list2(const list2 <T> &a)
{
    CreateList();
    CopyList(a);
}*/
 
template <class T>
list2 <T>::~list2()
{
    gobeg();
 
    while( !isempty() )
    {
        gonext();
        delcurrent();
        goprev();
    }
}
 
 
 
template <class T>
int list2 <T>::gonext()
{
    if(atend()) return -1;
current=current->next;
 
}
 
template <class T>
int list2 <T>::goprev()
{
    if(atbeg()) return -1;
    current=current->prev;
}
 
template <class T>
void list2 <T>::gobeg()
{
    while(!atbeg())
    current=current->prev;
}
 
template <class T>
void list2 <T>::goend()
{
    while(!atend())
    current=current->next;
}
//++
template <class T>
void list2 <T>::addbefore(T x)
{
    listitem <T> *pos;
    //pos=(listitem *)malloc(sizeof(listitem));
    //if(!pos) return -1;
 
    pos->prev=current->prev;
    pos->next=current;
    current->prev->next=pos;
    current->prev=pos;
    pos->value=x;
    numofelem++;
}
//++
template <class T>
void list2 <T>::addafter(T x)
{
    listitem <T> *pos;
    //pos=(listitem <T> *)malloc(sizeof(listitem));
    //if(!pos) return -1;
 
    pos->next=current->next;
    pos->prev=current;
    current->next->prev=pos;
    current->next=pos;
    pos->value=x;
    numofelem++;
 
 
}
/*
template <class T>
bool list2 <T>::GetBefore(T &x)
{
    if( AtBeg() ) return false;
 
    x = before -> value;
    after -> prev = before -> prev;
    before -> prev -> next = after;
 
    delete before;
 
    before = after -> prev;
 
    return true;
}
 
template <class T>
bool list2 <T>::GetAfter(T &x)
{
    if(AtEnd()) return false;
 
    x = after -> value;
    before -> next = after -> next;
    after -> next -> prev = before;
 
    delete after;
 
    after = before -> next;
 
    return true;
}*/
 
 
/*
template <class T>
bool list2 <T>::DelBefore()
{
    if(AtBeg()) return false;
 
    after -> prev = before -> prev;
    before -> prev -> next = after;
 
    delete before;
 
    before = after -> prev;
 
    return true;
}
 
template <class T>
bool list2 <T>::DelAfter()
{
    if(AtEnd()) return false;
 
    before -> next = after -> next;
    after -> next -> prev = before;
 
    delete after;
 
    after = before -> next;
 
    return true;
}
*/
//++
template <class T>
void list2 <T>:: delcurrent()
{
    listitem <T> *pos;
    if(isempty()) cout<<"cant delete current element - list is empty!!!"<<endl;
 
    current->prev->next=current->next;
    current->next->prev=current->prev;
    pos=current;
    current=current->next;
    numofelem--;
    free(pos);
}
//++
template <class T>
T &list2 <T>::currentval()
{
    if( atbeg() )
    {
        cout << "\a";
    }
    return current->value;
}
//++
template <class T>
bool list2 <T>::isempty()
{
    return base.next==base.prev;
}
//++
template <class T>
bool list2 <T>::atbeg()
{
    return current==base.next;
}
//++
template <class T>
int list2 <T>::numelem()
{
    return numofelem;
}
//++
template <class T>
bool list2 <T>::atend()
{
    return current==base.prev;
 
}
 
template <class T>
void list2 <T>::printlistleft2right()
{
gobeg();
    while (!atend())
     {
     cout<<current->value<<"\n";
     gonext();
     }
     cout<<"\nend of output left2right\n";
 }
template <class T>
void list2 <T>::printlistright2left()
{
goend();
    while (!atbeg())
     {
     cout<<current->value<<"\n";
     goprev();
     }
     cout<<"\nend of output right2left\n";
 }
 
int main()
{
    char c;
    int i;
    list2 <int> a;
    a.createlist2();
    //list2 <int> a;
    int temp;
    int pqr=1;
    while(pqr==1)
    {
        cout << "Test program for integers" << endl;
        cout << "\t1: addbefore" << endl;
        cout << "\t2: addafter" << endl;
        cout << "\t3: deletecurrent" << endl;
        cout << "\t4: first item?" << endl;
        cout << "\t5: last item?" << endl;
        cout << "\t6: currentvalue" << endl;
        cout << "\t7: isempty or not?" << endl;
        cout << "\t8: numberofelements" << endl;
        cout << "\t9: PRINT LEFT2RIGHT" << endl;
        cout << "\t10: PRINT RIGHT2LEFT" << endl;
        cout << "\tx: Exit" << endl << endl;
 
        cout << "Choose key: ";
        cin >> c;
 
        switch (c)
        {
        case '1':
            cout << "Insert new item (before) : ";
            cin >> i;
            temp=a.currentval();
            a.addbefore(temp);
            break;
        case '2':
            cout << "Insert new item (after) : ";
            cin >> i;
            temp=a.currentval();
            a.addafter(temp);
            break;
        case '3':
            cout << "deleting current element...";
            a.delcurrent();
            break;
        case '4':
            a.gobeg();
            cout << "first item is " << a.currentval() << endl;
            break;
        case '5':
            a.goend();
            cout << "last item is " << a.currentval() << endl;
            break;
        case '6':
            cout << "current element value" << a.currentval() << endl;
            break;
        case '7':
            if(!a.isempty()) cout << "list not empty" << endl;
            else cout << "list is empty" << endl;
            break;
        case '8':
            temp=a.numelem();
            cout << "you will get the number of elements.... now!" << temp << endl;
            break;
        case '9':
            a.printlistleft2right();
                break;
        case '10':
            a.printlistright2left();
                break;
        case 'x':
            //system("cls");
            pqr=0;
        default:
            cout << "Input error, it seems..." << endl;
        }
 
        system("pause");
        //system("cls");
    }
return 0;
}