Question

How does the code below work ? where is the counter for the for-loop and how can i reset the counter to line number 0.

for (std::string line;std::getline(ifs, line); )
{
}

Answer 1

There is no need for a counter. This is equivalent to

std::string line;
while(getline(ifs, line))
{
}

There are methods to move the input iterator back to the beginning of the file. Something like: ifs.seekg(0, std::ios::beg); should do the trick.