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

 1 #include<iostream>
 2 using namespace std;
 3
 4 class Object
 5 {
 6 public:
 7     Object(int num) :num_(num)
 8     {
 9         cout << "Object..." <<num_<<"..."<< endl;
10     }
11     ~Object()
12     {
13         cout << "~Object..." << num_ << "..." << endl;
14     }
15 private:
16     int num_;
17 };
18 class Container
19 {
20 public:
21     Container(int obj1=0, int obj2=0):obj1_(obj1), obj2_(obj2)
22     {
23         cout << "Container..." << endl;
24     }
25     ~Container()
26     {
27         cout << "~Container..." << endl;
28     }
29 private:
30     Object obj1_;
31     Object obj2_;
32 };
33 int main(void)
34 {
35     Container c(10,20);//先构造Object，再是Container析构次序相反
36
37     return 0;
38 }

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

 1 #include<iostream>
 2 using namespace std;
 3
 4 //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
 5 class Object
 6 {
 7 public:
 8     Object(int num=0) :num_(num), kNum_(num), redNum_(num_)
 9     {
10         //kNum_=100;  ERROR
11         //redNum_ = num;  ERROR
12         cout << "Object..." << num_ << "..." << endl;
13     }
14     ~Object()
15     {
16         cout << "~Object..." << num_ << "..." << endl;
17     }
18 private:
19     int num_;
20     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
21     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
22 };
23
24 int main(void)
25 {
26     Object obj(10);
27
28     return 0;
29 }

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;
}