Why is this so much slower in C++?

Question

I have converted this simple method from C# to C++. It reads a path table and populates a list of lists of ints (or a vector of vectors of ints).

A sample line from

Answer 1

The whileloop in your code seems to be very messy and long, as it is doing things in a way which is not needed:

A simple and fast equivalent code would be this:

int result;
stringstream ss(line);
while ( ss >> result ) //reads all ints untill it encounters non-int
{
    pathLookupVectors[i][j].push_back(result);
}

In C++, such loop is idiomatic as well. Or instead of this manual loop, you could write use std::copy ¹:

std::copy(std::istream_iterator( ss ), 
          std::istream_iterator(), 
          std::back_inserter(pathLookupVectors[i][j]));

^{1. It is taken from @David's comment.}

Or even better if you do this, when you push_back the vector itself:

 if (getline(myFile, line)) //enter if a line is read successfully
 {
   stringstream ss(line);
   std::istream_iterator begin(ss), end;
   pathLookupVectors[i].push_back(vector(begin, end));
 }

Done!