我用c++写了一个简单的领接表小程序，编译的时候报错 代码如下

#include <iostream>
#include <list>

using namespace std;

class Network;
class Node{
private:
    int number; // 节点序号
    int infected_step; // 节点受感染时间
    bool is_infected; // 节点是否被感染
    friend class Network;
public:
    Node(int val) {number = val; infected_step = -1; is_infected = false;};
    ~Node();
};
class Network{
private:
    int network_size;
    list<Node>* graph;
public:
    Network(const int val);
    ~Network();
    void print();
    void addEdge(int number1, int number2);
    void deleteEdge(int number1, int number2);
};
Network::Network(const int val){
    network_size = val;
    graph = new list<Node>[val + 1];
}
Network::~Network(){
    delete[] graph;
}

void Network::addEdge(int number1, int number2){
    Node node1(number1), node2(number2);
    graph[number1].push_back(node2);
    graph[number2].push_back(node1);
}

报错如下：

Undefined symbols for architecture x86_64:

"Node::~Node()", referenced from:

  Network::addEdge(int, int) in test-07ef30.o
  std::__1::__list_imp<Node, std::__1::allocator<Node> >::clear() in test-07ef30.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)