C ++未定义对模板类方法的引用 [英] C++ undefined reference to template class method

问题描述

我总是获得

未定义的引用`Graph :: InsertVertex（std :: string）'

undefined reference to `Graph::InsertVertex(std::string)'

如果我编译我的项目！任何提示为什么他不能解决这个参考？
（所有文件都在netbeans项目文件夹中）

if I compile my project! Any hints why he cant resolve this reference? (all Files are in the netbeans project folder)

// main.cpp

#include <cstdlib>
#include <string>
#include "Graph.h"

using namespace std;

int main(int argc, char** argv)
{
    Graph<string> *graph = new Graph<string>(); // <--- ERROR

    graph->InsertVertex("A");

    return 0;
}

// Node.h

// Node.h

#include <iostream>
#include "Graph.h"

template<class T> 
class Node
{   

friend class Graph;    

public:
    Node(T val)
    {
        this->data = val;
        this->vertList = NULL;
        this->next = NULL;
    }

    Node(const Node& orig);
    virtual ~Node();

private:
    T data;
    Node<T> *vertList;
    Node<T> *next;
    int status;

};

// Graph.h

#include <iostream>
#include "Node.h"

template <class T> 
class Graph 
{    
public:
    Graph()
    {
        head = NULL;        
    }

    void InsertVertex(T val);    
    void InsertEdge(T v_val, T e_val);

    void PrintVertices();
    void PrintEdges(T v_val);

    void DeleteEdge(T v_val, T e_val);   
    void DeleteVertex(T val);

    void bfs();    

private:
    Node<T> *head;

};

// Graph.cpp

#include "Graph.h"

template <class T>
void Graph<T>::InsertVertex(T val)
{
    Node<T> *temp = new Node<T>(val);

    if(head == NULL) head = temp;
    else
    {
        Node<T> node = head;

        while(node->vertList != NULL)
            node = node->vertList;

        node->vertList = temp;
    }   
}

template <class T>
void Graph<T>::InsertEdge(T v_val, T e_val)
{
    if (head != NULL)
    {
        Node<T> *k = head;
        Node<T> *t = head;
        Node<T> *temp = new Node<T> (e_val);        

        while (t != NULL)
        {
            if (t->data == v_val)
            {
                Node<T> *s = t;

                while (s->next != NULL)
                    s = s->next;

                s->next = temp;

                while (k != NULL)
                {
                    if(k->data == e_val) break;

                    k = k->vertList;
                }

                temp->vertList = k;
                return;
            }

            t = t->vertList;
        } // end while loop        
    }
    else std::cout << "Add first vertices to the graph" << std::endl;
}

template <class T>
void Graph<T>::PrintEdges(T v_val)
{
    Node<T>* t = head;

    while (t != NULL)
    {
        if (t->data == v_val)
        {
            while (t->next != NULL)
            {
                std::cout << t->next->vertList->data << "   ";
                t = t->next;
            }
        }
        t = t->vertList;
    }
}

template <class T>
void Graph<T>::PrintVertices()
{
    Node<T>* t = head;

    while (t != NULL)
    {
        std::cout << t->data << "   ";
        t = t->vertList;
    }
}

推荐答案

你想要你的模板方法在标题中，所以他们在需要时编译。如果你真的想隐藏它在实现文件中，你必须显式实例化 Graph.cpp 如

Typically you want your template methods in the header, so they are compiled when needed. In case you really want to hide it in the implementation file, you have to explicitly instantiate the template in Graph.cpp like

template class  Graph<string>;

因为你必须为每个类型 T 你打算使用 Graph< T> ，模板类的点有点失败，你最好把所有的东西放在标题

Since you have to do that for every type T you intend to use with Graph<T>, the point of the template class is somewhat defeated and you better put everything into the header

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