流的问题

我正在完成这段代码，但我想知道为什么我不能使用 ofstream 输出存档。

我做错了什么？

问题出在第 61 行。编译器说：错误，'struct std：：stringstream' 没有名为 aux4 的成员。

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <string.h>
#include <fstream>
#include <math.h>
#include <iostream>
#include <sstream>

using namespace std;

class  validate { 
       public:
              int aa, mm , dd ;
              string guy;
       public:
              validate ( int x, int y, int z){
                      aa=x; mm=y; dd=z;
              }
       bool check ( int aa, int mm, int dd){
            if ( aa >0){
               if( mm == 01 || mm== 03 || mm == 05 || mm == 07 || mm == 08.0 || mm == 10 || mm == 12){
                   return dd <=31;
                   }
               else if ( mm == 04 || mm == 06 || mm == 09.0 || mm == 11){
                    return dd <=30;
                    }
               else {
                    return dd <=28;
               }
            }
       }
};
int main (){
    int aa, mm, dd, key;
    string name, date, aux1, aux2, aux3;
    stringstream aux4;
    do {
        cout<<"Name:"<<endl;
        cin>>name;
        cout<<"Enter date of birth:"<<endl;
        cin>>date;
        aux1= date.substr(6,9); 
        aa = atoi(aux1.c_str());
        aa=2012-aa;
        aux2= date.substr(3,4);
        aux2=aux2.substr(0,2);
        mm = atoi(aux2.c_str());
        aux3= date.substr(0,2);
        dd = atoi(aux3.c_str());
        aux4 << dd << mm << ".txt";
        ofstream file(aux4.aux4().c_str(), fstream ::app);
        file<<aa<<"years"<<name<<endl;
        file.close();

        cout<<"Enter key != 0 if you want to continue ( Ideally press 1):"<<endl;
        cin>>key;
    }while ( key != 0);
    cout<<"Thanks! End of line."<<endl;
    system ("PAUSE");
    return 0;
};