Files and parsing input

A C++ command-line tool usually reads a text file, such as a CSV of transactions, and turns each line into a struct (a small record type). Reading files uses std::ifstream and std::getline, and you split the fields with std::istringstream.

Convert text with std::stoi or std::stod, which throw std::invalid_argument on bad text. Catch that exception and report the line number, so users can fix their file. Decide what a bad line means: skip it with a warning, or stop.

Check that the stream opened, and remember that relative paths are worked out from where the program runs. Keep parsing in its own function that returns a std::vector of structs, so the core logic and the tests never touch files.