vitual 函数

虚函数：通过基类对象指针指向派生类对象，或通过基类对象引用来引用派生类对象

#include <iostream>
#include <string>

using std::cout;
using std::endl;
using std::cin;
using std::string;

class ex0{
	public: 
	virtual string show(){
		return "0号异常";;
	}
};
class ex1 : public ex0
{
	public:
	string show()
	{
	return "1号异常";
	}
};
class ex2 : public ex0
{
	public:
	string show()
	{
	return "2号异常";
	}
};
class ex3 : public ex0
{
	public:
	string show()
	{
	return "3号异常";
	}
};
int main()
{
	ex1 a;
	ex2 b;
	ex3 c;
	cout<<"请输入一个异常编号:"<<endl;
	int n;
	cin>>n;
	try
	{  
		switch(n)
		{
		case 1: throw a;
		case 2: throw b;
		case 3: throw c;
		default:  cout<<"输入的数不在范围之内."<<endl;
		}
	}
	catch(ex0 & e)
	{ 
	cout<<"在main函数中捕获了"<<e.show()<<endl;
	}
//	catch(ex2 e )
//	{
//	cout<<"在main函数中捕获了"<<e.show()<<endl;
//	}
//	catch(ex3 e)
//	{
//	cout<<"在main函数中捕获了"<<e.show()<<endl;
//	}
	return  0;
}

#include <iostream>
#include <string>
using namespace std;
class Person
{
public:
	Person(string i="10000",string na="noname",int a=0,char s='M') //Person类构造函数
	{
		id = i;
		name = na;
		age = a;
		sex = s;
	}
	void SetData(string i="10000",string na="noname",int a=0,char s='M') //修改信息
	{
		id = i;
		name = na;
		age = a;
		sex = s;
	}
	virtual void ShowInfo( )  //定义虚函数
	{
		cout<<endl;
		cout<<"Id:    "<<id<<endl;
		cout<<"name:  "<<name<<endl;
		cout<<"age:   "<<age<<endl;
		cout<<"sex:   "<< (sex=='M'?"Man":"Woman") <<endl;
	}
protected:
	string    id;
	string   name;
	int     age;
	char    sex;
};  //End of Person
class UnderGraduate:virtual public Person
{
public:
	UnderGraduate(string i,string na,int a,char s,string ma,float sc) //构造函数
		:Person(i,na,a,s)          //初始化列表
	{
		major = ma;
		score = sc;
	}
	void SetData(string i,string na,int a,char s,string ma,float sc) //修改信息
	{
		Person::SetData(i,na,a,s);
		major = ma;
		score = sc;
	}
	void ShowInfo()  //显示信息
	{
		cout<<endl;
		Person::ShowInfo();
		cout<<"major: "<<major<<endl;
		cout<<"score: "<<score<<endl;
	}
protected:
	string    major;
	float   score;
};  //End of UnderGraduate
class Teacher: virtual public Person
{
public:
	Teacher(string i,string na,int a,char s,float sa)  //Teacher类构造函数
			:Person(i,na,a,s),salary(sa)
	{		
	}
	void SetData(string i,string na,int a,char s,float sa)
	{
		Person::SetData(i,na,a,s);
		salary = sa;
	}
	void ShowInfo()
	{
		Person::ShowInfo();
		cout<<"salary: "<<salary<<endl;
	}
protected:
	float salary;
};  //End of Teacher
class Graduate:public UnderGraduate, public Teacher		// 从两个类继承
{
public:
	Graduate(string i,string na,int a,char s,string ma,float sc,float sa)
		:UnderGraduate(i,na,a,s,ma,sc),Teacher(i,na,a,s,sa),Person(i,na,a,s)
	{
	}
	void SetData(string i,string na,int a,char s,string ma,float sc,float sa)
	{   //修改信息
		Person::SetData(i,na,a,s);
		major = ma;
		score = sc;
		salary = sa;
	}
	void ShowInfo()  //显示信息
	{   
		cout<<endl;
		cout<<"Id:    "<<id<<endl;
		cout<<"name:  "<<name<<endl;
		cout<<"age:   "<<age<<endl;
		cout<<"sex:   "<< (sex=='M'?"Man":"Woman") <<endl;
		cout<<"major: "<<major<<endl;
		cout<<"score: "<<score<<endl;
		cout<<"salary:"<<salary<<endl;
	}
};  //End of Graduate
int main()
{
	Person * personPtr;  //定义基类Person的指针
	Person ObjectP("201302034","ZhangNing",21,'W');
	personPtr = &ObjectP;  //基类的指针指向基类Person的对象
	personPtr->ShowInfo();
	UnderGraduate ObjectUG("201302034","ZhangNing",21,'W',"Computer",98.5);
	personPtr = &ObjectUG;  //基类的指针指向派生类UnderGraduate的对象
	personPtr->ShowInfo();
	Teacher ObjectT("201302034","ZhangNing",21,'W',1800);
	personPtr = &ObjectT;  //基类的指针指向派生类Teacher的对象
	personPtr->ShowInfo();
	Graduate ObjectG("201302034","ZhangNing",21,'W',"Computer",98.5,1800);
	personPtr = &ObjectG;  //基类的指针指向派生类Graduate的对象
    personPtr->ShowInfo();
    return 0;
}