3.3 派生类的构造与析构函数

3.3.1 构造

• 如果子类构造函数没有显式指明基类部分（基类子对象）的初始化方式，那么编译器将会自动调用基类的无参构造函数来初始化基类子对象。

• 如果希望以有参的方式来初始化基类部分，那么必须使用初始化列表来显式指明

• 子对象构造顺序

  • 分配内存
  • 构造基类子对象（按继承表顺序）
  • 构造成员子对象（按声明顺序）
  • 执行子类构造函数代码

  #include <iostream>
  using namespace std;class Member{
  private:int m_m;
  public:Member(){cout << "Member()" << endl;}Member(int m) {cout << "Member(int)" << endl;m_m = m;}
  };class Base {
  private:int m_i;
  public:Base(){cout << "Base()" << endl;}Base(int i){cout << "Base(int)" << endl;m_i = i;}
  };class Derived:public Base{
  private:int m_d;Member m_me;
  public:Derived(){cout << "Derived()" << endl;//不指定作用域 默认调用无惨构造函数}Derived(int d):Base(d), m_me(d){ //指定作用域 就调用有参构造函cout << "Derived(int)" << endl;m_d = d;}
  };
  int main (void) {Derived d1;Derived d2(100);return 0;
  }
  

3.3.2 析构

• 子类的析构函数，无论自己定义的，还是编译器缺省提供，都会自动调用基类的析构函数，完成基类子对象的销毁

• 子类对象销毁过程

  • 执行子类析构函数代码
  • 析构成员子对象（按声明逆序）
  • 析构基类子对象（按继承表逆序）
  • 释放内存

  #include <iostream>
  using namespace std;class Member{
  private:int m_m;
  public:Member(){cout << "Member()" << endl;}Member(int m) {cout << "Member(int)" << endl;m_m = m;}~Member(){cout << "~Member()" << endl;}
  };class Base {
  private:int m_i;
  public:Base(){cout << "Base()" << endl;}Base(int i){cout << "Base(int)" << endl;m_i = i;}~Base(){cout << "~Base()" << endl;}
  };class Derived:public Base{
  private:int m_d;Member m_me;
  public:Derived(){cout << "Derived()" << endl;//不指定作用域 默认调用无惨构造函数}Derived(int d):Base(d), m_me(d){ //指定作用域 就调用有参构造函cout << "Derived(int)" << endl;m_d = d;}~Derived(){cout << "~Derived()" << endl;}
  };
  int main (void) {Derived d1;return 0;
  }//输出结果：
  myubuntu@ubuntu:~/lv19/cplusplus/dy03$ ./a.out 
  Base()
  Member()
  Derived()
  ~Derived()
  ~Member()
  ~Base()