未定义的引用错误c ++，但包含头文件？

Question

我刚写了一个创建链表的简单程序。当我在一个文件（main.cpp）中编写整个程序时，程序编译并运行正常。但是，当我将程序分成头文件，实现文件和main时，它不起作用。我得到错误“对List :: AddNode（int）的未定义引用。我不明白为什么......

头文件

#ifndef LINKEDLIST_H_INCLUDED
#define LINKEDLIST_H_INCLUDED
#include <iostream>
using namespace std;

class List
{
 public:
     List();
     void AddNode(int addData);
     void DeleteNode(int deldata);
     void PrintList();


 private:
    struct Node
    {
        int data;
        Node* next;

    };

    Node* head;
    Node* curr;
    Node* temp;
};


#endif // LINKEDLIST_H_INCLUDED

List.cpp

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

List::List()
{
    head = nullptr;
    curr = nullptr;
    temp = nullptr;
}

void List::AddNode(int addData)
{
    nodePtr n = new Node;
    n->next = nullptr;
    n->data = addData;

    if(head !=nullptr)
    {
        curr = head;
        while(curr->next!=nullptr)
        {
            curr = curr->next; //This while loop advances the curr pointer to the next node in the list
        }
        curr->next = n; //now the last node in the list points to the new node we created. So our new node is now the last node
    }

    else
    {
        head = n;
    }

}

void List::DeleteNode(int delData)
{
    Node* delPtr = nullptr; //created a deletion pointer and set it equal to nothing (it's not pointing to anything)
    temp = head;
    curr = head;
    while(curr != nullptr && curr->data !=delData)
    {
       temp = curr;
       curr = curr->next;
    }
    if(curr==nullptr)
    {
        cout << delData << " was not in the list \n"
        delete delPtr;
    }
    else
    {
        delPtr = curr;
        curr = curr->next;
        temp->next = curr;
        delete delPtr;
        cout << "the value " << delData << "was deleted \n";
    }

}

void List::PrintList()
{
    head = curr;
    while(curr!=nullptr)
    {
        cout<<curr->data<<endl;
        curr = curr->next;
    }
}

的main.cpp

#include <iostream>
#include <cstdlib>
#include "List.h"


using namespace std;

int main()
{
    List crisa;
    crisa.AddNode(5);
}

当我尝试调用函数AddNode时，我在main.cpp文件中收到错误。我不知道为什么，这可能是编译问题吗？