[C++之旅] 15 深拷贝与浅拷贝

[C++之旅] 15 深拷贝与浅拷贝

• 拷贝构造函数分为深拷贝和浅拷贝两种方式
• 浅拷贝只是将被拷贝的对象的成员直接赋值给拷贝的对象，如对象中包含指针，则拷贝的对象与被拷贝的对象中的指针指向的为同一个地址。
• 面对对象中的指针，深拷贝则重新开辟内存，复制拷贝指针中的数据。

浅拷贝实例

main.cpp

#include <iostream>
#include "team.h"

using namespace std;

int main()
{
    Team team1(12);

    Team team2(team1);

    cout << "team1.num = " << team1.getnum() << endl;
    cout << "team2.num = " << team2.getnum() << endl;

    team1.printageAddr();
    team2.printageAddr();

    return 0;
}

Team.cpp

#include <iostream>
#include "team.h"

using namespace std;

Team::Team(int num) : m_num(num)
{
    //给m_age分配m_num个int的内存
    m_age = new int[m_num];
    cout<< "Team" <<endl;
}
Team::Team(const Team &team)
{
    m_age = team.m_age;
    m_num = team.m_num;
    cout<< "Team &" <<endl;
}

Team::~Team()
{
    delete []m_age;
    m_age = NULL;
    cout<< "~Team" <<endl;
}

void Team::setnum(int num)
{
    m_num = num;
}

int Team::getnum()
{
    return m_num;
}

void Team::printageAddr()
{
    cout << "m_age's address is " << m_age << endl;
}

Team.h

#ifndef __TEAM_H__
#define __TEAM_H__

class Team
{
public:
    Team(int num);
    Team(const Team &team);
    ~Team();
    void setnum(int num);
    int getnum();
    void printageAddr();
private:
    int m_num;
    int *m_age;
};


#endif

运行结果：

Team
Team &
team2.num = 12
m_age's address is 0x7fb939402750
m_age's address is 0x7fb939402750
~Team
a.out(2560,0x7fffb8419380) malloc: *** error for object 0x7fb939402750: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug

浅拷贝后m_age指针指向的是同一个位置，但是在释放m_age内存时，会释放两次，释放team1时释放一次0x7fb939402750，释放team2时会释放第二次，因此会出现最后几句话的错误信息。

深拷贝

main.cpp

#include <iostream>
#include "team.h"

using namespace std;

int main()
{
    Team team1(12);

    Team team2(team1);

    cout << "team1.num = " << team1.getnum() << endl;
    cout << "team2.num = " << team2.getnum() << endl;

    team1.printageAddr();
    team2.printageAddr();

    team1.printage();
    team2.printage();

    return 0;
}

Team.cpp

#include <iostream>
#include "team.h"

using namespace std;

Team::Team(int num) : m_num(num)
{
    //给m_age分配m_num个int的内存
    m_age = new int[m_num];
    for(int i = 0; i < m_num; i++)
        *(m_age + i) = i;
    cout<< "Team" <<endl;
}
Team::Team(const Team &team)
{
    m_num = team.m_num;
    m_age = new int[m_num];
    for(int i = 0; i < m_num; i++) {
        *(m_age + i) = *(team.m_age + i);
        //m_age[i] = team.m_age[i];
    }

    cout<< "Team &" <<endl;
}

Team::~Team()
{
    delete []m_age;
    m_age = NULL;
    cout<< "~Team" <<endl;
}

void Team::setnum(int num)
{
    m_num = num;
}

int Team::getnum()
{
    return m_num;
}

void Team::printageAddr()
{
    cout << "m_age's address is " << m_age << endl;
}

void Team::printage()
{
    for(int i = 0; i < m_num; i++)
        cout << *(m_age + i);
    cout << endl;
}

Team.h

#ifndef __TEAM_H__
#define __TEAM_H__

class Team
{
public:
    Team(int num);
    Team(const Team &team);
    ~Team();
    void setnum(int num);
    int getnum();
    void printageAddr();
    void printage();
private:
    int m_num;
    int *m_age;
};


#endif

运行结果：

Team
Team &
team1.num = 12
team2.num = 12
m_age's address is 0x7fc53c402750
m_age's address is 0x7fc53c402780
01234567891011
01234567891011
~Team
~Team

在上一个程序的基础上，修改了拷贝构造函数，拷贝指针变量时，先申请内存再对每个地址的值进行复制，并将指针的地址以及地址的内容输出，如上结果所示，两个地址不相同，但其内容相同，而且编译器没有报错哦。