gistfile1.txt

//An istream is passed in to the function as an argument so we don't need to worry about generating it. Referred to by "in".
string line; char key; string value; istringstream iss;
while (in.good()) {
  getline(in,line);
  iss.str(line);
  iss >> key;
  iss >> value;
  codeMap[key] = value;
}