Question

我试图用虚拟节点（centinels）实现Dequeue。当我试图编译时，我得到一个分段错误11错误。这是我的代码:(非常感谢!!）

Node.h：

#ifndef LINKEDDEQUE_H
#define LINKEDDEQUE_H

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

template <class Element>
class LinkedDeque {
public:
     LinkedDeque();
    ~LinkedDeque();
    LinkedDeque(const LinkedDeque<Element>& deque);
    bool isEmpty()const;
    void insertFront(const Element & element);
    void insertRear(const Element & element);
    void deleteFront();
    void deleteRear();
    void print();
    const Element& getFront()const;
    const Element& getRear()const;
private:
    int num_elements; 
    Node<Element> *_front; 
    Node<Element> *_rear; 
    Node<Element> *frontSentinel;
    Node<Element> *rearSentinel;
};

template <class Element>
LinkedDeque<Element>::LinkedDeque(){
    //creamos nodos vacios
    _front->setNext(frontSentinel);
    _rear->setPrevious(rearSentinel); //**************
    int num_elements = 0; 

    cout << "Holi" << endl;

}

//cal implementar el constructor copia
template <class Element>
LinkedDeque<Element>::LinkedDeque(const LinkedDeque<Element>& deque){

}

template <class Element>
LinkedDeque<Element>::~LinkedDeque() {
}

template <class Element>
bool LinkedDeque<Element>::isEmpty()const{
    return (this->frontSentinel->getNext()==nullptr);   
}

template <class Element>
void LinkedDeque<Element>::insertFront(const Element & element){
    Node<Element> *new_node = new Node<Element> (element); 
    if(isEmpty()){
        rearSentinel->setPrevious(new_node);
        frontSentinel->setNext(new_node); 
    }else{
        Node<Element> *aux;
        aux = frontSentinel->getNext();
        frontSentinel->setNext(new_node);
        aux->setPrevious(frontSentinel->getNext());
        delete aux;
    }
    num_elements++;

}
template <class Element>
void LinkedDeque<Element>::insertRear(const Element & element){
    Node<Element> *new_node = new Node<Element> (element); 
    if(isEmpty()){
        rearSentinel->setPrevious(new_node);
        frontSentinel->setNext(new_node);
    }else{
        Node<Element> *aux;
        aux = rearSentinel->getPrevious();
        rearSentinel->setPrevious(new_node);
        aux->setNext(rearSentinel->getPrevious());
        delete aux;
    }
    num_elements++;
}
template <class Element>
void LinkedDeque<Element>::deleteFront(){
    if(!isEmpty()){
        if(num_elements == 1){
            delete frontSentinel->getNext();
            frontSentinel->setNext(rearSentinel);
            rearSentinel->setPrevious(frontSentinel);
        }else {
            Node<Element> *aux;
            aux = frontSentinel->getNext();
            aux->getNext()->setPrevious(frontSentinel);
            frontSentinel->setNext(aux->getNext());
            delete aux;
        }
        num_elements--;
    }
}
template <class Element>
void LinkedDeque<Element>::deleteRear(){
    if(!isEmpty()){
        if(num_elements == 1){
            delete rearSentinel->getPrevious();
            rearSentinel->setPrevious(nullptr);
            frontSentinel->getPrevious(nullptr);
        }else{
            Node<Element> *aux;
            aux = rearSentinel->getPrevious();
            aux->getPrevious()->setNext(rearSentinel);
            rearSentinel->setPrevious(aux->getPrevious());
            delete aux;
        }
        num_elements--;
    }
}
template <class Element>
void LinkedDeque<Element>::print(){
    if(!isEmpty()){
        Node<Element> *printController = frontSentinel->getNext();
        while( printController->getNext()!= nullptr){
            cout<< printController->getElement() << endl;
            printController = printController->getNext();
        }
    }
}

template <class Element>
const Element& LinkedDeque<Element>::getFront()const{
    return frontSentinel->getNext()->getElement();
}
template <class Element>
const Element& LinkedDeque<Element>::getRear()const{
    return rearSentinel->getPrevious()->getElement();
}

#endif /* LINKEDDEQUE_H */

LinkedDeque.h：

#include <cstdlib>
#include"Node.h"
#include"LinkedDeque.h"
using namespace std;

/*
 * 
 */
int main(int argc, char** argv) {
    LinkedDeque<int> *deque= new LinkedDeque<int>;
    deque->insertFront(4);
    deque->insertFront(5);
    deque->insertRear(10);
    deque->deleteFront();
    deque->print();

}

最后，main.cpp：

{{1}}

也许我不应该实现Node的析构函数并为它虚拟化？或者指针声明有一些错误？

Answer 1

我猜你的LinkedDeque构造函数模板正在访问无效的_front，_rear指针

template <class Element>
LinkedDeque<Element>::LinkedDeque(){
    //creamos nodos vacios
    _front->setNext(frontSentinel); //*_front has not been initialized and contains undefined values*
    _rear->setPrevious(rearSentinel); //**************
    int num_elements = 0; 

    cout << "Holi" << endl;

}

Answer 2

您可以使用new Node<Element>(NULL);构建标记，以便LinkedDeque有Node<Element>个对象用作标记而不是nullptr。从以下方法中的这些更改开始：

template <class Element>
LinkedDeque<Element>::LinkedDeque(){
    //creamos nodos vacios
    frontSentinel = new Node<Element>(NULL);
    rearSentinel  = new Node<Element>(NULL);
    rearSentinel->setPrevious(frontSentinel);
    frontSentinel->setNext(rearSentinel);
    int num_elements = 0;

    cout << "Holi" << endl;
}
template <class Element>
bool LinkedDeque<Element>::isEmpty()const{
    return this->frontSentinel->getNext()->getElement()==NULL;
}

template <class Element>
void LinkedDeque<Element>::insertFront(const Element & element){

    Node<Element> *new_node = new Node<Element>(element); 
    new_node->setNext(frontSentinel->getNext());
    frontSentinel->getNext()->setPrevious(new_node);
    new_node->setPrevious(frontSentinel);
    frontSentinel->setNext(new_node);

    num_elements++;
}

template <class Element>
void LinkedDeque<Element>::insertRear(const Element & element){

    Node<Element> *new_node = new Node<Element> (element); 
    new_node->setPrevious(rearSentinel->getPrevious());
    rearSentinel->getPrevious()->setNext(new_node);
    new_node->setNext(rearSentinel);
    rearSentinel->setPrevious(new_node);

    num_elements++;
}

template <class Element>
void LinkedDeque<Element>::deleteFront(){

    Node<Element> *aux = frontSentinel->getNext();
    aux->getNext()->setPrevious(frontSentinel);
    frontSentinel->setNext(aux->getNext());
    delete aux;

    num_elements--;
}

template <class Element>
void LinkedDeque<Element>::deleteRear(){

    Node<Element> *aux = rearSentinel->getPrevious();
    aux->getPrevious()->setNext(rearSentinel);
    rearSentinel->setPrevious(aux->getPrevious());
    delete aux;

    num_elements--;
}

template <class Element>
void LinkedDeque<Element>::print(){
    Node<Element> *printController = frontSentinel->getNext();
    while (printController->getElement() != NULL) {
        cout << printController->getElement() << endl;
        printController = printController->getNext();
    }
}

分段错误：11错误

2 个答案: