c++ - << 使用继承和模板定义

Question

<分区>

Answer 1

删除 friend std::ostream& operator<<(std::ostream& outputStream, const LinkedList<T>& sec);来自 LinkedList 类定义。您已经在此 header 中拥有此类运算符的模板化版本，并且链接器告诉您非模板化版本缺少实现。 链表.h:

#ifndef LINKEDLIST_H
#define LINKEDLIST_H

#include <string>
#include <iostream>

template<class T> class LinkedList;

// Class representing a templated linkedlist element
template<class T> class LLElement {
    friend class LinkedList<T>;
public:
    // Constructor
    LLElement(T* p_Data) : data(p_Data), next(NULL) {}

    T* getData() const { return data; }
    LLElement<T>* getNext() { return next; }
private:
    LLElement<T>* next;
    T* data;
};

// Class representing a templated linked list
template<class T> class LinkedList {
public:
    LinkedList() : size(0), start(NULL) {}
    LinkedList(const LinkedList&);
    ~LinkedList();

    unsigned int getSize() const { return size; }
    LLElement<T>* getStart() const { return start; }

    //adds shallow copy of T to the LinkedList
    void sortedAdd(T*);
    //removes the first occurence of T from the LinkedList
    void remove(T*);
    //merges existing LinkedList with given LinkedList
    void merge(const LinkedList<T>&);
    //formatted print of LinkedList to given outputstream
    void showLinkedList(std::ostream& p_Out) const;
    //friend std::ostream& operator<<(std::ostream& outputStream, const LinkedList<T>& sec);

private:
    LLElement<T>* start;
    unsigned int size;
};

//LinkedList copy constructor
//TODO
template<class T>  LinkedList<T>::LinkedList(const LinkedList<T>& a){
    this->size=a.getSize();
    this->start=a.getStart();
}

// LinkedList destructor
// TODO
template<class T> LinkedList<T>::~LinkedList(){
    LLElement<T>* a=this->getStart();
    LLElement<T>* b=a->next;
    while(a!=NULL){
        delete a;
        a=b;
        b=a->next;
    }

}


// sortedAdd
// adds shallow copy of T to the LinkedList
// TODO
template<class T> void LinkedList<T>::sortedAdd(T* add){
    LLElement<T>* a=new LLElement<T>(add);
    LLElement<T>* b=this->getStart();
    while(!(*(b->data)<=*(a->getData()))){
        b=b->next;
    }
    a->next=b->next;
    b->next=a;
    this->size++;
}



// remove
// removes the first occurence of T from the LinkedList
// TODO
template<class T> void LinkedList<T>::remove(T* ab){
    LLElement<T>* a=this->getStart();
    LLElement<T>* b=this->getStart();
    while(a!=NULL){
        if(*(a->data)==*(ab)){
            if(b==a){
                this->start=a->next;
                delete a;
                this->size--;
                return;
            }
            b->next=a->next;
            delete a;
            this->size--;
            return;
        }
        b=a;
        a=b->getNext();
    }
}


// TODO output operator

template<class T>  std::ostream& operator<<(std::ostream& outputStream, const LinkedList<T>& sec){
    sec.showLinkedList(outputStream);
    return outputStream;
}
//merges existing LinkedList with given LinkedList
template<class T> void LinkedList<T>::merge(const LinkedList<T>& p_LL){
    LLElement<T> *cursor = p_LL.start;
    while (cursor != NULL){
        sortedAdd(cursor->data);
        cursor = cursor->next;
    }
}

//formatted print of LinkedList to given outputstream
template<class T> void LinkedList<T>::showLinkedList(std::ostream& p_Out) const {
    LLElement<T>* current = start;
    int counter = 1;
    p_Out << "LINKEDLIST OF SIZE " << size << std::endl;
    while (current != NULL){
        p_Out << "LL ELEMENT " << counter++ << " : ";
        p_Out << *(current->getData()) << std::endl;
        current = current->getNext();
    }
}

#endif

此外，关于 Content.h:

bool CMSContent::operator< (const CMSContent& param) const;
bool CMSContent::operator<= (const CMSContent& param) const;
bool CMSContent::operator== (const CMSContent& param) const;

应该是

bool operator< (const CMSContent& param) const;
bool operator<= (const CMSContent& param) const;
bool operator== (const CMSContent& param) const;