Fun with C++

A simple code to open a file and write something and read from a file...(C++)
But something is wrong here..
Let me know...what it is!!!

Comment below..!!!!

#include<iostream>
#include<sstream>
#include<fstream>
using namespace std;
int main()
{
        fstream fobj;
        string filename = "/home/ferdose/Desktop/file.txt";
        string str;
        fobj.open("filename",ios::in|ios::out);
        if(!fobj) cerr<<"Can't open"<<endl;
        fobj>>str;
        fobj<<"hey"<<endl<<"hello";
        cout<<str;
}