Input integers from fstream to 2d vector< vector<int> > C++

Question

I am trying to use push_back to dynamically add integers from an ifstream to a 2d vector. Basically input will be fed in similar to :

3
20 3
30 4
40 5 
3
50 6
60 7
70 8

and I want to read the int's by themselves (3,3 ..etc), and then create the 2d vector of the pairs of numbers (the int's by themselves describe how many pairs there will be). Right now I am using getline() and storing the digits in a char, then converting them to int's again, but I feel that this may not be ideal. If anyone has any ideas I would appreciate it.

Answer 1

Something like (untested):

std::istream_iterator<int> eos;
std::vector<std::vector<int>> matrix;
while(std::getline(str, line))
{
  std::istringstream istr(line);
  std::istream_iterator<int> iin(istr);
  std::vector<int> columns;
  std::back_insert_iterator<vector<int>> back_it(columns);
  std::copy(iin, eos, back_it);
  matrix.push_back(columns);
}