bool FilmData::findMedium(Medium& m) {
	// Find returns an iterator pointing to the set end (one beyond the last element) if the element isn't in the set
	if(media_.find(m) != media_.end())
		return true;
	return false;
}

Line 1: error: 'FilmData' has not been declared
compilation terminated due to -Wfatal-errors.