Use std::transform and a std::stringstream for this.

std::stringstream str;

std::transform(
    recordingArray.begin(),
    recordingArray.end(),
    std::ostream_iterator<std::string>(str, ", "),
    [](const std::pair<int, QString> &p) { return std::to_string(p.first) + ", " + p.second.toStdString(); });