我调用max_element哪出错了

[ycm_113]

#include<iostream>
#include<vector>
#include<string>
#include<algorithm>
using namespace std;
class student
{
public:
student(){}
student(string name,int age)
{
this->name=name;
this->age;
}
string GetName()
{ return name;}
int GetAge()
{ return age;}
private:
string name;
int age;
};
bool comp(const student &s1,const student &s2)
{
return s1.GetAge()<s2.GetAge();
}
int main()
{
vector<student> vs;
vs.push_back(student("zhang",19));
vs.push_back(student("wang",12));
vs.push_back(student("li",21));
vs.push_back(student("sun",6));
cout<<(*vs.begin()).GetName()<<endl;
cout<<vs.back().GetName()<<endl;
cout<<"年龄最大的学生:"<<max_element(vs.begin(),vs.end(),comp)->GetName()<<endl;
system("pause");
return 0;
}
这个程序编译不能通过,我把comp函数的const去掉,就能通过了,为什么?
另外,去掉const后输出的结果也不正确?请高手指点一下我这个程序哪里错了

[paidfighting]

给GetAge加上const也可以

const对象只能调用const函数

[paidfighting]

#include <iostream>  
#include <vector>  
#include <string>  
#include <algorithm>  
using namespace std;  
class student  
{  
public:  
	student(){}  
	student(string name,int age)  
	{  
		this->name=name;  
		this->age;  
	}  
	string GetName()  
	{ return name;}  
	int GetAge() const 
	{ return age;}  
private:  
	string name;  
	int age;  
};  
bool comp(const student &s1,const student &s2)  
{  
	return s1.GetAge() < s2.GetAge();  
}  
int main()  
{  
	vector <student> vs;  
	vs.push_back(student("zhang",19));  
	vs.push_back(student("wang",12));  
	vs.push_back(student("li",21));  
	vs.push_back(student("sun",6));  
	cout <<(*vs.begin()).GetName() <<endl;  
	cout <<vs.back().GetName() <<endl;  
	cout <<"年龄最大的学生:" <<max_element(vs.begin(),vs.end(),comp)->GetName() <<endl;  
	system("pause");  
	return 0;  
} 

[ryfdizuo]

貌似没什么问题了，或者用sort函数排序,

[paidfighting]

粗心的lz

构造函数：

student(string name,int age)
{
this->name = name;
this->age = age;
}

[ttkk_2007]

class student  
{  
public:  
student(){}  
student(string name,int age)  
{  
this->name=name;  
this->age=age;   //1.露了=age
}  
string GetName()  
{ return name;}  
int GetAge() const  //2.露了const
{ return age;}  
private:  
string name;  
int age;  
};  
bool comp(const student &s1,const student &s2)  
{  
return s1.GetAge() <s2.GetAge();  
}  
int main()  
{  
vector<student> vs;  
vs.push_back(student("zhang",19));  
vs.push_back(student("wang",12));  
vs.push_back(student("li",21));  
vs.push_back(student("sun",6));  
cout <<(*vs.begin()).GetName() <<endl;  
cout <<vs.back().GetName() <<endl;  
cout <<"年龄最大的学生:" <<max_element(vs.begin(),vs.end(),comp)->GetName() << endl;  

return 0;  
} 

[hastings]

顶5楼,典型的const问题;
LZ在写成员函数时,若它不会改变成员,则最好加上const,
有时候同一成员函数需要两个版本,const版本和非const版本.
如重载*和->时.

[hastings]

正是由于C++中的成员函数有const和非const的区别,
所以才有写时复制的技术.VC6.0的string类就是写时复制.