#include <iostream>
#include <exception>
using namespace std;
class LQueue
{
private:
    struct QItem 
    {
        int info;
        QItem* next;
        QItem* prev;
        QItem(int Ainfo): info(Ainfo), next(NULL), prev(NULL) {}
    };
    QItem *front, *rear;
    unsigned size;
    void Erase();
    void Clone(const LQueue&);
    void DeleteItem(QItem*);
    void* PtrByIndex(unsigned) const;
public:
    LQueue(): front(NULL), rear(NULL), size(0) {};
    LQueue(const LQueue&);
    LQueue& operator = (const LQueue&);
    ~LQueue();
    void PushF(int);
    void PushB(int);
    bool PopF(int&);
    bool PopB(int&);
    bool Pop();
    bool Del(unsigned);
    const int& GetByIndex(unsigned) const;
    void SetByIndex(int,unsigned);
    void Browse(void ItemWork(int)) const;
    
};
LQueue::LQueue(const LQueue& Q)
{
    Clone(Q);
}
LQueue::~LQueue()
{
    Erase();
}
LQueue& LQueue::operator = (const LQueue& Q) 
{
    if (this != &Q) 
    {
        Erase();
        Clone(Q);
    }
    return *this;
}

void LQueue::Erase()
{
    while (Pop());
    size = 0;
}
void LQueue::Clone(const LQueue& Q)
{
    QItem *tmp = Q.front;
    for (unsigned i=0; i<Q.size; i++) 
    {
        PushB(tmp->info);
        tmp = tmp->next;
    }
}
void LQueue::PushF(int Ainfo)
{
    QItem* tmp = new QItem(Ainfo);
    if (size>0)
    {
        tmp->next = front;
        front->prev=tmp;
    }
    else
    {
        front = tmp;
        rear=tmp;
    }
    front = tmp;
    size++;
}
void LQueue::PushB(int Ainfo)
{
    QItem* tmp = new QItem(Ainfo);
    if (size>0)
    {
        rear->next = tmp;
        tmp->prev=rear;
    }
    else
        front = tmp;
    rear = tmp;
    size++;
}
bool LQueue::PopF(int& Ainfo)
{
    if (size==0) 
        return false;
    Ainfo=front->info;
    QItem *tmp = front;
    front = front->next;
    delete tmp;
    size--;
    if (size==0)
        rear = NULL;
    return true;
}
bool LQueue::PopB(int& Ainfo)
{
    if (size==0) 
        return false;
    Ainfo=rear->info;
    QItem *tmp = rear;
    rear = rear->prev;
    delete tmp;
    size--;
    if (size==0)
        rear = NULL;
    return true;
}

const int& LQueue::GetByIndex (unsigned k) const 
{
    if ((k<0) || (k>=size))
        throw exception("Impossible to execute operator[]: invalid index");
    QItem *tmp = front;
    for (unsigned i=0; i<k; i++)
        tmp = tmp->next;
    return tmp->info;
}
void LQueue::SetByIndex(int zna,unsigned k)
{    
    if ((k<0) || (k>=size))
        throw exception("Impossible to execute operator[]: invalid index");
    QItem *tmp = front;
    for (unsigned i=0; i<k; i++)
        tmp = tmp->next;
    tmp->info=zna;
}
void ItemWork(int HHH)
{
    cout << HHH << " ";
}
void LQueue::Browse(void ItemWork(int)) const 
{
    QItem *tmp = front;
    for (unsigned i=0; i<size; i++)
    {
        ItemWork(tmp->info);
        tmp = tmp->next;
    }
}

void LQueue::DeleteItem(QItem* jj)
{
    QItem* tmp=jj;
    (jj->prev)->next=jj->next;
    (jj->next)->prev=jj->prev;
    delete tmp;
}
void* LQueue::PtrByIndex(unsigned k) const
{        
    if ((k<0) || (k>=size))
        throw exception("Impossible to execute operator[]: invalid index");
    QItem *tmp = front;
    for (unsigned i=0; i<k; i++)
        tmp = tmp->next;
    return tmp;
}
bool LQueue::Del(unsigned k)
{
    QItem* mmp=(QItem*)PtrByIndex(k);
    DeleteItem(mmp);
    return true;
}
bool LQueue::Pop()
{
    if (size==0) 
        return false;
    QItem *tmp = front;
    front = front->next;
    delete tmp;
    size--;
    if (size==0)
        rear = NULL;
    return true;
}
int main()
{
    try
    {
        setlocale(LC_ALL,".1251");
        LQueue kk;
        int h;
        kk.PushF(7);
        kk.PushF(77);
        kk.PushF(73);
        kk.PushB(70);
        kk.PushF(75);
        kk.PushF(79);
        cout << "Создание: ";
        kk.Browse(ItemWork);
        cout << endl;
        cout << "Оператор присваивания: ";
        LQueue jj;
        jj=kk;
        jj.Browse(ItemWork);
        cout << endl;
        cout << "Конст. коп.: ";
        LQueue jjk(kk);
        jjk.Browse(ItemWork);
    }
    catch(exception e)
    {
        cout << e.what() << endl;
    }
}

Наверное, у Вас просто не проинициализированы внутренние поля класса LQueue:

Спасибо большое feodorv