Read-group extraction without temporary buffer

gistfile1.cpp

while (getline(in, line)) {
    if (line.compare(0, 4, "@RG\t") != 0) continue;
    size_t start = line.find("\tID:");
    if (start == string::npos) continue;
    start += 4;
    size_t end = line.find("\t", start);
    if (end == string::npos or end == start) continue;
    gids.emplace(string.begin() + start, string.begin() + end);
    // Or, in C++03:
    //gids.insert(line.substr(start, end - start));
}