c ++中的命令设计模式问题

Question

我以这种方式实现了命令设计模式，但是如果我在命令类中取消注释析构函数，则会产生链接错误。为什么？

#include <iostream>

using namespace std;
//command design pattern


class command
{
public:
    virtual void execute() = 0;
    //virtual ~command();

};


class Receiver
{
public :
    void action()
    {
        cout<<" command executed "<<endl;
    }

};

class concreteCommand:public command
{
    Receiver *_r;
public:
    concreteCommand(Receiver *r = 0) :_r(r)
    {}
    void setReceiver(Receiver *r = 0)
    {
        _r = r;
    }
    virtual void execute()
    {
        if(0!=_r)
        {
            _r->action();
        }
    }
};

class invoker
{
    command *_c;
public:
    invoker(command* c):_c(c)
    {}
    void setCommand(command *c=0)
    {
        _c=c;
    }
    void invoke()
    {
        if(0!=_c)
        {
            _c->execute();
        }
    }

};





int main()
{
    Receiver r;
    concreteCommand c(&r);
    invoker i(&c);
    i.invoke();
    return 0;
}

Answer 1

发现错误。我必须提供析构函数的主体。