C++语法基础--派生类的构造函数，赋值操作符，析构函数，虚析构函数

秒速五厘米 2021-12-21 13:49 256阅读 0赞

**1.如果派生类定义了自己的构造函数（复制构造函数）或赋值操作符，该构造函数（复制构造函数）或赋值操作符一般应显式使用基类构造函数（复制构造函数）或赋值操作符初始化基类部分、  
Eample:  
 class base  
\{  
public:  
base()  
\{  
\}  
  
base(int i):x(i)  
\{  
cout<<"base::constructor"<<endl;  
\}  
  
base(base& other)  
\{  
cout<<"base::copy"<<endl;  
x=other.x;  
\}  
  
base& operator=(base &other)  
\{  
cout<<"base::assign"<<endl;  
x=other.x;  
\}  
  
  
int x;  
\};  
  
class derived:public base  
\{  
public:  
derived()  
\{  
\}  
derived(int i,int j):base(i),y(j)  
\{  
cout<<"derived::constructor"<<endl;  
\}  
  
derived(derived& other):base(other)  
\{  
cout<<"derived::copy"<<endl;  
y=other.y;  
\}  
  
derived& operator=(derived& other)  
 \{  
  base::operator=(other);  
  cout<<"derived::assign"<<endl;  
 y=other.y;  
 \}  
  
 void fun()  
\{  
cout<<"derived:\\n"<<x<<ends<<y<<endl;  
\}  
  
private:  
int y;  
  
\};  
  
int main()  
\{  
derived d(1,2);//constructor  
 d.fun();  
  
 cout<<endl;  
  
 derived d1(d);//copy-constructor  
 d1.fun();  
  
 cout<<endl;  
  
 derived d2;  
 d2=d1; //assign  
 d2.fun();  
  
 return 0;  
 \}  
  
  
  
运行结果：  
  
![Center][]  
  
  
  
  
  
  
  
  
2.析构函数  
 \*编译器总是显式调用派生类对象基类部分的析构函数，每个析构函数只负责清除自己的成员  
\*首先运行派生类析构函数，然后按继承层次依次向上调用各基类析构函数  
  
Example：  
 class base  
\{  
public:  
~base()  
\{  
cout<<"base::~base()"<<endl;  
\}  
  
\};  
  
class derived:public base  
\{  
public:  
~derived()  
\{  
cout<<"derived::~derived()"<<endl;  
\}  
  
\};  
  
int main()  
\{  
  
base \*pb=new derived;  
delete pb;  
cout<<endl;  
  
derived d;  
return 0;  
\}  
  
  
Output:  
base::~base()  
  
derived::~derived()  
base::~base()**

**3.虚析构函数**

**\*析构函数为虚函数，通过指针调用时，运行的析构函数将因指针所指对象类型的不同而不同**

**从上面结果可以看出，当delete pb时，只调用了基类的析构函数，派生类定义的析构函数并没有被调用，解决办法，把基类的析构函数声明为虚析构函数**

**Example:  
class base  
\{  
public:  
virtual~base()  
\{  
cout<<"base::~base()"<<endl;  
\}  
  
\};  
  
class derived:public base  
\{  
public:  
~derived()  
\{  
cout<<"derived::~derived()"<<endl;  
\}  
  
\};  
  
int main()  
\{  
  
base \*pb=new derived;  
delete pb;  
  
return 0;  
\}  
  
  
Output:  
  
  
 derived::~derived()  
base::~base()**

[Center]: /images/20211220/d3dbd1f394b44a25a9902586d4dea461.png