C++学习笔记（4）——派生类的构造函数和析构函数

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例1：观从派生类向基类传递参数

/**//************************************************************************


* 派生类的构造函数和析构函数


************************************************************************/


#include <IOSTREAM.H>


//基类


class CBase




...{


int x;


public:




CBase(int n)...{cout<<"the base class constructor!"<<endl; x=n; }




~CBase() ...{cout<<"the base class deconstructor!"<<endl;}




virtual void showx()...{cout<<"in the base class x = "<<x<<endl;} //此处有没有virtual效果一样


};




//派生类


class CDerive:public CBase




...{


int y;


public:




CDerive(int n,int m):CBase(m)...{ cout<<"the derived class constructor!"<<endl; y=n; }




~CDerive()...{cout<<"the derived class deconstructor!"<<endl;}




void showy()...{ cout<<"in the derived class y = "<<y<<endl; }


};


main()




...{ CDerive obj1(123,456);


obj1.showx();


obj1.showy();


CBase obj2(1234);


obj2.showx();


return 0;


}


运行结果：

例2：调用派生类的构造函数时默认调用基类的构造函数

/**//************************************************************************


* 派生类的构造函数和析构函数


************************************************************************/


#include <IOSTREAM.H>


//基类


class CBase




...{


int x;


public:




CBase()...{ cout<<"the base class constructor!"<<endl; x=100;}




~CBase()...{cout<<"the base class deconstructor!"<<endl;}




virtual void showx()...{cout<<"in the base class x = "<<x<<endl; } //此处有没有virtual效果一样


};




//派生类


class CDerive:public CBase




...{


int y;


public:




CDerive()...{cout<<"the derived class constructor!"<<endl; y=200;}




~CDerive()...{cout<<"the derived class deconstructor!"<<endl;}




void showy()...{ cout<<"in the derived class y = "<<y<<endl; }


};




main()




...{


CDerive obj1;


obj1.showx();


obj1.showy();


CBase obj2;


obj2.showx();


return 0;


}


运行结果：

例3：派生类和基类同名成员函数的调用

/**//************************************************************************


* 派生类的构造函数和析构函数


************************************************************************/


#include <IOSTREAM.H>


//基类


class CBase




...{


int x;


public:




CBase()...{ cout<<"the base class constructor!"<<endl; x=100;}




~CBase()...{cout<<"the base class deconstructor!"<<endl;}




virtual void show()...{cout<<"in the base class x = "<<x<<endl;} //此处有没有virtual效果一样


};




//派生类


class CDerive:public CBase




...{


int y;


public:




CDerive()...{cout<<"the derived class constructor!"<<endl; y=200;}




~CDerive()...{cout<<"the derived class deconstructor!"<<endl;}




void show()...{cout<<"in the derived class y = "<<y<<endl;}


};




main()




...{


CDerive obj1;


obj1.CBase::show();


obj1.show();


CBase obj2;


obj2.show();


return 0;


}


运行结果：