"=" 重载，如何深度copy

[joly_zl]

#include <iostream>
using namespace std;

class vehicle
{
public:
	vehicle()
	{
		mMaxSpeed=0;mMaxWeight=0;num=0;
		cout<<"vehicle constructor"<<endl;
	}
	vehicle(int sp,int we,int n)
	{
		mMaxSpeed=sp;mMaxWeight=we;num=n;

	}
	~vehicle(){cout<<"vehicle unconstructor"<<endl;}

	vehicle(const vehicle& vv)
	{
		num=vv.num;
		mMaxSpeed=vv.mMaxSpeed;
		mMaxWeight=vv.mMaxWeight;

		cout<<"vehicle copy-constructor"<<endl;
	}
	
	vehicle& operator =(const vehicle& vv)//"="重载
	{
		num=vv.num;
		mMaxSpeed=vv.mMaxSpeed;
		mMaxWeight=vv.mMaxWeight;
		return *this;
	}

	virtual int getMaxSpeed(){cout<<"get Maxspeed vehicle\n";return mMaxSpeed;}
	virtual int getMaxWeight(){cout<<"get MaxWeight vehicle\n";return mMaxWeight;}
	virtual void setNum(int n){cout<<"set num vehicle\n";num=n;}

	virtual void setMaxSpeed(int speed){cout<<"set Maxspeed vehicle\n"; mMaxSpeed=speed;}
	virtual void setMaxWeight(int weight){cout<<"set MaxWeight vehicle\n"; mMaxWeight=weight;}

protected:
	int mMaxSpeed;
	int mMaxWeight;
private:
	int num;
};

class car :public vehicle
{
public:
	car()
	{
		type=0;
		cout<<"car constructor\n";
	}
	car(const car& cc):vehicle(cc)
	{
		/*mMaxSpeed=cc.mMaxSpeed;
		mMaxWeight=cc.mMaxWeight;*/
		type=cc.type;
		cout<<"car copy constructor!"<<endl;

	}
	car& operator =(const car& cc)//如何实现vehicle类中 的private 变量num赋值？？？？？
	{
		//
		mMaxSpeed=cc.mMaxSpeed;
		mMaxWeight=cc.mMaxWeight;
		type=cc.type;
		return *this;
	}
private:
	int type;
};

int main()
{
	//test vehicle the base class;
	vehicle v;
	vehicle v1(v);
	vehicle v2;
	v2.setMaxSpeed(33);
	v2.setMaxWeight(55);
	vehicle v3=v2;
	vehicle v4(v2);
	int speed=v2.getMaxSpeed();
	int weight=v2.getMaxWeight();
	v=v2;
//////////////////////test over!
	car c;
	car c1;
	c.setMaxSpeed(12);
	c.setMaxWeight(33);
	c.setNum(11);

	c1=c;
	car c2(c);
	car c3=c;
	car c4;
	c4=c;
	
}

[joly_zl]

help

[fallening]

class C
{
private:
void do_copy( const C& c );//just make this one perfect
......
public:
C(){}
C(const C& c){do_copy(c);}
C& operator = ( const C& c){do_copy(c);}
......
};

[fallening]

class C
{
    private:
        void do_copy( const C& c );//just make this one perfect
        ......
    public:
        C(){}
        C(const C& c){do_copy(c);}
        C& operator = ( const C& c){do_copy(c);}
        ......
};

[fallening]

class C
{
private:
void do_copy( const C& c );//just make this one perfect
......
public:
C(){}
C(const C& c){operator=(c);}
C& operator = ( const C& c){do_copy(c); return *this;}
......
};

[tangshuiling]

不存在指针类成员，无需实现所谓的深COPY,换句话说vehicle v3=v2; v3与v2没有彼此依存的关系

[joly_zl]

我错了，不是copy,
是子类的“=”重载是也要给基类的private成员赋值

[joly_zl]

[Quote=引用 3 楼 fallening 的回复:]
C/C++ codeclass C
{
private:
void do_copy( const C& c );//just make this one perfect
......
public:
C(){}
C(const C& c){do_copy(c);}
C& operator = ( const C& c){do_copy(c);}
......
};
[/Quote]
void do_copy( const C& c ) 如果C为子类，那么这个函数能给他的父类的private成员赋值？

[s79947171]

//基类的
 vehicle& operator =(const vehicle& vv)//"="重载
    {
        if(this==&vv)//判断是否为自己赋值
        {
           return *this;
        }
        num=vv.num;
        mMaxSpeed=vv.mMaxSpeed;
        mMaxWeight=vv.mMaxWeight;
        return *this;
    }
//派生的
    car& operator =(const car& cc)    
    {
        vehicle::operator =(cc);//调用基类的重载操作符,因为cc换个对象一定含有基类私有成员的值，但是不知道你这么做有和意义，基类的私有成员虽然被派生类集成了，但是是不可访问的，意义何在？
        mMaxSpeed=cc.mMaxSpeed;
        mMaxWeight=cc.mMaxWeight;
        type=cc.type;
        return *this;
    }
//最后就是如果成员中没有动态申请空间的数据，完全没有必要定义深度拷贝构造函数和重载=操作符
//一个类如果开始什么都没有，编译器会自动生成
1  默认构造函数   2  默认析构函数  3 默认重载=操作符 4 默认生成拷贝构造函数  5 默认当前对象地址this

上面是我的理解，如果错了，请别介意，技术问题大家多多探讨

[fairchild811]

子类可以给父类private赋值，活着public或者通过函数

[fairchild811]

sorry，是或者

[joly_zl]

问题解决了：
总结一下：
父类的private成员最好是用父类的接口来copy

#include <iostream>
using namespace std;

class vehicle
{
public:
	vehicle()
	{
		mMaxSpeed=0;mMaxWeight=0;num=0;
		cout<<"vehicle constructor"<<endl;
	}
	vehicle(int sp,int we,int n)
	{
		mMaxSpeed=sp;mMaxWeight=we;num=n;

	}
	~vehicle(){cout<<"vehicle unconstructor"<<endl;}

	vehicle(const vehicle& vv)
	{
		num=vv.num;
		mMaxSpeed=vv.mMaxSpeed;
		mMaxWeight=vv.mMaxWeight;

		cout<<"vehicle copy-constructor"<<endl;
	}
	
	vehicle& operator =(const vehicle& vv)//"="重载
	{
		num=vv.num;
		mMaxSpeed=vv.mMaxSpeed;
		mMaxWeight=vv.mMaxWeight;
		return *this;
	}

	virtual int getMaxSpeed(){cout<<"get Maxspeed vehicle\n";return mMaxSpeed;}
	virtual int getMaxWeight(){cout<<"get MaxWeight vehicle\n";return mMaxWeight;}
	virtual void setNum(int n){cout<<"set num vehicle\n";num=n;}
	virtual void setNum(const vehicle& v){cout<<"set num vehicle\n";num=v.num;}

	virtual void setMaxSpeed(int speed){cout<<"set Maxspeed vehicle\n"; mMaxSpeed=speed;}
	virtual void setMaxWeight(int weight){cout<<"set MaxWeight vehicle\n"; mMaxWeight=weight;}

protected:
	int mMaxSpeed;
	int mMaxWeight;
private:
	int num;
private:
	void do_copy(const vehicle& vv)
	{
		num=vv.num;
		mMaxSpeed=vv.mMaxSpeed;
		mMaxWeight=vv.mMaxWeight;
	}
};

class car :public vehicle
{
public:
	car()
	{
		type=0;
		cout<<"car constructor\n";
	}
	car(const car& cc)
	{
		setNum(cc);
		mMaxSpeed=cc.mMaxSpeed;
		mMaxWeight=cc.mMaxWeight;
		type=cc.type;
		cout<<"car copy constructor!"<<endl;

	}
	car& operator =(const car& cc)//如何实现vehicle类中 的private 变量num赋值？？？？？
	{
		//
		setNum(cc);
		mMaxSpeed=cc.mMaxSpeed;
		mMaxWeight=cc.mMaxWeight;
		type=cc.type;
		return *this;
	}
private:
	int type;
};

int main()
{
	//test vehicle the base class;
	vehicle v;
	vehicle v1(v);
	vehicle v2;
	v2.setMaxSpeed(33);
	v2.setMaxWeight(55);
	vehicle v3=v2;
	vehicle v4(v2);
	int speed=v2.getMaxSpeed();
	int weight=v2.getMaxWeight();
	v=v2;
//////////////////////test over!
	car c;
	car c1;
	c.setMaxSpeed(12);
	c.setMaxWeight(33);
	c.setNum(11);

	c1=c;
	car c2(c);
	car c3=c;
	car c4;
	c4=c;
	
}

[s79947171]

上面忘记写了，派生类重载=操作符的时候也要检查是否自赋值 ，不然当数据中有需要动态开辟内存的数据在调用的时候会出错误的

  if(this==&cc)//判断是否为自己赋值
        {
           return *this;
        }

[fairchild811]

没有指针变量，应该不存在深度copy吧

[joly_zl]

vehicle::operator =(cc);//调用基类的重载操作符,因为cc换个对象一定含有基类私有成员的值，但是不知道你这么做有和意义，基类的私有成员虽然被派生类集成了，但是是不可访问的，意义何在？

c.setMaxSpeed(12);
c.setMaxWeight(33);
c.setNum(11);
c1=c;的时候
c1.num也等于c.num;

[joly_zl]

[Quote=引用 13 楼 fairchild811 的回复:]
没有指针变量，应该不存在深度copy吧
[/Quote]
不是copy的问题是,"="重载的问题。

[arong1234]

基类如果private成员，它应该提供public或者protected接口让你设置值，这样你在operator＝内调用这个函数不就可以了？
合理的方法是：基类自己也定义operator=(如果这个类是你自己定义，而你要实现拷贝，你永远要实现拷贝构造和operator=)，在这种情况下，你直接调用基类operator=即可

[waizqfor]

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