3-3 拷贝构造函数

深拷贝与浅拷贝

深浅拷贝是面试经典问题，也是常见的一个坑
浅拷贝：简单的赋值拷贝操作
深拷贝：在堆区重新申请空间，进行拷贝操作
示例：

class Person {
public:
    //无参（默认）构造函数
    Person() {
        cout << "无参构造函数!" << endl;
    }
    //有参构造函数
    Person(int age ,int height) {
        cout << "有参构造函数!" << endl;
        m_age = age;
        m_height = new int(height);
    }
    //拷贝构造函数  
    Person(const Person& p) {
        cout << "拷贝构造函数!" << endl;
        //如果不利用深拷贝在堆区创建新内存，会导致浅拷贝带来的重复释放堆区问题
        m_age = p.m_age;
        m_height = new int(*p.m_height);
    }
    //析构函数
    ~Person() {
        cout << "析构函数!" << endl;
        if (m_height != NULL)
        {
            delete m_height;
        }
    }
public:
    int m_age;
    int* m_height;
};
void test01()
{
    Person p1(18, 180);
    Person p2(p1);
    cout << "p1的年龄： " << p1.m_age << " 身高： " << *p1.m_height << endl;
    cout << "p2的年龄： " << p2.m_age << " 身高： " << *p2.m_height << endl;
}
int main() {
    test01();
    system("pause");
    return 0;
}

总结：如果属性有在堆区开辟的，一定要自己提供拷贝构造函数，防止浅拷贝带来的问题

//This is an error program
#include <iostream>
using namespace std;
class Person {
public:
    Person() {
        m_age = 0;
        m_ph = NULL;
        cout << "Default Construct function" << endl;
    }
    Person(int age,int h) {
        cout << "Person's Parametric Constructed function" << endl;
        m_age = age;
        m_ph = new int(h);
    }
    ~Person() {
        //堆区开辟的数据释放，在析构函数中释放
        if (m_ph != NULL) {
            delete m_ph;
            m_ph = NULL;
        }
        cout << "Person's Destruct function" << endl;
    }
    int m_age;
    int* m_ph;
};
void exam() {
    Person p1(18,160);
    cout << "Age of p1 is " << p1.m_age << endl;
    cout << "height of p1 is " << *p1.m_ph << endl;
    Person p2(p1);
    cout << "Age of p2 is " << p2.m_age << endl;
    cout << "height of p2 is " << *p2.m_ph << endl;
}
int main() {
    exam(); 
}

#include <iostream>
using namespace std;
class Person {
public:
    Person() {
        m_age = 0;
        m_ph = NULL;
        cout << "Default Construct function" << endl;
    }
    Person(int age,int h) {
        cout << "Person's Parametric Constructed function" << endl;
        m_age = age;
        m_ph = new int(h);
    }
    Person(const Person& p) {
        cout << "Person's copy function" << endl;
        m_age = p.m_age;
        //m_ph = p.m_ph; // This is how the complier does;
        m_ph = new int(*p.m_ph);
        //Problem solved
    }
    ~Person() {
        //堆区开辟的数据释放，在析构函数中释放
        if (m_ph != NULL) {
            delete m_ph;
            m_ph = NULL;
        }
        cout << "Person's Destruct function" << endl;
    }
    int m_age;
    int* m_ph;
};
void exam() {
    Person p1(18,160);
    cout << "Age of p1 is " << p1.m_age << endl;
    cout << "height of p1 is " << *p1.m_ph << endl;
    Person p2(p1);
    cout << "Age of p2 is " << p2.m_age << endl;
    cout << "height of p2 is " << *p2.m_ph << endl;
}
int main() {
    exam(); 
}