Re: Differences in reading from an istream vs. stringstream

Given the following input file:

bob 1 2 3 4 5
mary 2 3 4 5 6 7
susan 3 4 5 6 7 8 9

This code snippet does not read it correctly:

class Student
{
public:
   ...
private:
   std::string _Name;
   std::vector<int> _Grades;
};
...
/***** this only gets called once *****/
std::istream& operator>>(std::istream& is, Student& s)
{
   string name = "";
   is >> name;
   std::vector<int> grades;
   std::copy(std::istream_iterator<int>(is),
std::istream_iterator<int>(), std::back_inserter(grades));

   /***** at this point, name and the grades vector are correct for
the 'first' line in the input file *****/
   s.setName(name);
   s.setGrades(grades);
   return is;
}
...
std::ifstream fin;
std::vector<Student> students;
std::copy(std::istream_iterator<Student>(fin),
std::istream_iterator<Student>(), std::back_inserter(students));
/***** at this point, the students vector is empty *****/

If I change operator>> to read from a stringstream instead, it works
as expected.

std::istream& operator>>(std::istream& is, Student& s)
{
   std::string name = "";
   is >> name;

   std::string sGrades = "";
   std::getline(is, sGrades);

   std::stringstream ss(sGrades);

   std::vector<int> grades;
   std::copy(std::istream_iterator<int>(ss),
std::istream_iterator<int>(), std::back_inserter(grades));

   s.setName(name);
   s.setGrades(grades);

   return is;
}

So even though the one (and only) call to operator>> read the first
line of the file and assigned the values to the Student parameter, the
students vector got nothing added to it. Why would changing to a
stringstream fix this?