这是一个把学生按总分成绩排序的程序，但他vs2012这里说rank不明确是什么意思

#include<iostream>
#include<string>
using namespace std;

template<class T>
void rank(T *a)
{
    T temp;
    int i,j;
    for(i=0;i<5;i++)
    {
        for(j=0;j<(6-i-1);j++)
        {
            if((a+j)->sum>(a+j+1)->sum)
            {
                temp=a[j];
                a[j]=a[j+1];
                a[j+1]=temp;
            }
        }
    }
   
};

class student
{
public:
    char name[20];
    long int ID;
    int mathscore;
    int chinesescore;
    int englishscore;
    int sum;
public:
    student(char *n=0,long int id=0,int ms=0,int cs=0,int es=0)
    {
        *name=*n;
        ID=id;
        mathscore=ms;
        chinesescore=cs;
        englishscore=es;
    }
    void add()
    {
        sum=mathscore+chinesescore+englishscore;
    }
   
};

void main()
{   
    int i,a[6];
    student stu[6]={student("zhang",001,80,86,90),student("han",002,98,85,85),student("he",003,86,94,82),
                    student("liu",004,98,95,96),student("fang",005,98,78,86),student("gao",006,95,85,74)};
   
    for(i=0;i<6;i++)
    {
        stu[i].add();
        cout<<stu[i].name<<"\t"<<stu[i].ID<<"\t"<<stu[i].mathscore<<"\t"<<
            stu[i].chinesescore<<"\t"<<stu[i].englishscore<<"\t"<<endl;
    }
   
    for(i=0;i<6;i++)
    {
        a[i]=stu[i].sum;
    }

    rank(stu);
   
    for(i=0;i<6;i++)
    {
        cout<<stu[i].name<<"\t"<<stu[i].ID<<"\t"<<stu[i].mathscore<<"\t"<<
            stu[i].chinesescore<<"\t"<<stu[i].englishscore<<"\t"<<endl;
    }
   
   
}