C++笔记----构造函数与析构函数（三）

1、构造函数初始化列表

    推荐在构造函数初始化列表中进行初始化

    构造函数的执行分为两个阶段：初始化段、 普通计算段  

2、对象成员及其初始化

#include<iostream>
using namespace std;

class Object
{
public:
    Object(int num) :num_(num)
    {
        cout << "Object..." <<num_<<"..."<< endl;
    }
    ~Object()
    {
        cout << "~Object..." << num_ << "..." << endl;
    }
private:
    int num_;
};
class Container
{
public:
    Container(int obj1=0, int obj2=0):obj1_(obj1), obj2_(obj2)
    {
        cout << "Container..." << endl;
    }
    ~Container()
    {
        cout << "~Container..." << endl;
    }
private:
    Object obj1_;
    Object obj2_;
};
int main(void)
{
    Container c(10,20);//先构造Object，再是Container析构次序相反

    return 0;
}

3、const成员、引用成员的初始化

    const成员的初始化只能在初始化列表中进行

#include<iostream>
using namespace std;

//对象成员（对象所对应的类没有默认构造函数）的初始化，只能在构造函数初始化列表中进行
class Object
{
public:
    Object(int num=0) :num_(num), kNum_(num), redNum_(num_)
    {
        //kNum_=100;  ERROR
        //redNum_ = num;  ERROR
        cout << "Object..." << num_ << "..." << endl;
    }
    ~Object()
    {
        cout << "~Object..." << num_ << "..." << endl;
    }
private:
    int num_;
    const int kNum_;  //const成员的初始化只能在构造函数初始化列表中进行
    int& redNum_;     //引用成员的初始化只能在构造函数初始化列表中进行
};

int main(void)
{
    Object obj(10);

    return 0;
}

加入枚举类型

#include<iostream>
using namespace std;

class Object
{
public:
    enum E_TYPE
    {
        TYPE_A=100,
        TYPE_B=200
    };
public:
    Object(int num=0) :num_(num), kNum_(num), redNum_(num_)
    {
        cout << "Object..." << num_ << "..." << endl;
    }
    ~Object()
    {
        cout << "~Object..." << num_ << "..." << endl;
    }
    void DisplaykNum_()
    {
        cout << "kNum_" << kNum_ << endl;
    }
private:
    int num_;
    const int kNum_;  
    int& redNum_;     
};

int main(void)
{
    Object obj1(10);
    Object obj2(20);
    obj1.DisplaykNum_();
    obj2.DisplaykNum_();
    cout << obj1.TYPE_A << endl;
    cout << obj2.TYPE_A << endl;
    cout << Object::TYPE_A << endl;
    return 0;
}