拷貝構(gòu)造函數(shù)

拷貝構(gòu)造函數(shù)是使用類對(duì)象的引用作為參數(shù)的構(gòu)造函數(shù)，它能夠?qū)?shù)的屬性值拷貝給新的對(duì)象，完成新對(duì)象的初始化。
通常在一下三種情況下，程序會(huì)自動(dòng)調(diào)用拷貝構(gòu)造函數(shù)。

1.使用一個(gè)對(duì)象初始化另一個(gè)對(duì)象

#include <iostream>
#include<string>
using namespace std;
class Car
{
    public:
        Car(){};    //初始化構(gòu)造函數(shù)
        Car(string name, int seats);
        Car(Car &con_refcar);
        ~Car();    //析構(gòu)函數(shù)
    private:
        string m_name;
        int m_seats;
};
Car::Car(string name, int seats)
{
    m_name = name;
    m_seats = seats;
}
Car::Car(Car &con_refcar)
{
    m_name = con_refcar.m_name;          
    m_seats = con_refcar.m_seats;
}
Car::~Car() {}
int main()
{
    Car mynewcar("rrrr2", 4);
    Car myseccar(mynewcar);   //用一個(gè)對(duì)象對(duì)另一個(gè)對(duì)象初始化
    return 0;
}

2.對(duì)象作為實(shí)參傳遞給函數(shù)參數(shù)

#include <iostream>
#include<string>
using namespace std;
class Car
{
    public:
        Car(){};    //初始化構(gòu)造函數(shù)
        Car(string name, int seats);
        Car(Car &con_refcar);
        void print();
        ~Car();    //析構(gòu)函數(shù)
    private:
        string m_name;
        int m_seats;
};
Car::Car(string name, int seats)
{
    m_name = name;
    m_seats = seats;
}
Car::Car(Car &con_refcar)
{
    m_name = con_refcar.m_name;          
    m_seats = con_refcar.m_seats;
}
Car::~Car() {}
void Car::print()
{
    cout<<"name: "<<m_name<<endl;
    cout<<"sizes: "<<m_seats<<endl;
}
void print_carinfo(Car carinfo)  //對(duì)象最為實(shí)參傳遞給函數(shù)
{
    carinfo.print();
}
int main()
{
    Car mynewcar("rrrr2", 4);
    print_carinfo(mynewcar);  //調(diào)用該函數(shù)
    return 0;
}

3.函數(shù)返回值為類對(duì)象，創(chuàng)建臨時(shí)對(duì)象作為返回值

#include <iostream>
#include<string>
using namespace std;
class Car
{
    public:
        Car(){};    //初始化構(gòu)造函數(shù)
        Car(string name, int seats);
        Car(Car &con_refcar);
        Car get_carinfo();     //****
        void print();
        ~Car();    //析構(gòu)函數(shù)
    private:
        string m_name;
        int m_seats;
};
Car::Car(string name, int seats)
{
    
    m_name = name;
    m_seats = seats;
}
Car::Car(Car &con_refcar)
{

    m_name = con_refcar.m_name;          
    m_seats = con_refcar.m_seats;
}
Car::~Car()
{
}
void Car::print()
{
    cout<<"name: "<<m_name<<endl;
    cout<<"sizes: "<<m_seats<<endl;
}
Car Car::get_carinfo()    //關(guān)鍵函數(shù)
{
    Car tmp(m_name, m_seats);      //定義類對(duì)象
    return tmp;       //返回類對(duì)象
} 
int main()
{
    Car mynewcar("rrrr2", 4);
    Car ret;
    ret = mynewcar.get_carinfo();     //ret接受返回的類對(duì)象
    ret.print();
    return 0;
}

以上都是淺拷貝, 淺拷貝有個(gè)特點(diǎn)就是：類的私有成員不需要new出新的空間，像上面的m_name都是用string類型；如果換成char類型，上面的程序就會(huì)出錯(cuò)，原因是，淺拷貝并未為拷貝對(duì)象開(kāi)辟空間，只是讓拷貝對(duì)象的地址指向被拷貝對(duì)象的地址，相當(dāng)于“引用”。為了解決這個(gè)問(wèn)題，就要用到深拷貝！

深拷貝

#include <iostream>
#include<string>
using namespace std;
class Car
{
    public:
        Car(char *name, int seats);     
        Car(Car &con_refcar);
        ~Car();
    private:
        char *m_name;     //char型數(shù)據(jù)成員
        int m_seats;
};
Car::Car(char *name, int seats)
{
    int len = strlen(name) + 1;
    m_name = new char[len];      //每個(gè)對(duì)象初始化都要臨時(shí)開(kāi)劈空間
    strcpy(m_name, name );      //字符串之間賦值要用strcpy()函數(shù)
    m_seats = seats;
}
Car::Car(Car &con_refcar)       //深拷貝
{

    m_name = new char[strlen(con_refcar.m_name)+1];    //淺拷貝無(wú)需開(kāi)劈空間，數(shù)據(jù)成員賦值需要開(kāi)辟空間的都只能用深拷貝實(shí)現(xiàn)！
    strcpy(m_name,con_refcar.m_name);       
    m_seats = con_refcar.m_seats;
}
Car::~Car()
{
    delete[] m_name;
}
int main()
{
    char c[] = "rrrr2";
    Car mynewcar(c, 4);
    Car myseccar(mynewcar);
    return 0;
}

若有錯(cuò)，望指出