blah.cpp

template <class Key, class T>
QString mapToString(QMap<Key, T> &map){
    // this is derivative of the code that qDebug uses to serialize a QVariantMap
    // qtbase/src/corelib/io/qdebug.h
    // template <class Key, class T>
    // inline QDebug operator<<(QDebug debug, const QMap<Key, T> &map)

    QByteArray buf;
    QDataStream s(&buf, QIODevice::ReadWrite);
    s << "(";
    for (typename QMap<Key, T>::const_iterator it = map.constBegin(); it != map.constEnd(); ++it) {
        s << '(' << it.key() << ", " << it.value() << ')';
    }
    s << ')';
    return QString::fromLatin1(buf);
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QVariantMap map;
    map.insert("a", QVariant("123"));
    map.insert("b", QVariant("234"));

    qDebug() << mapToString(map);

    return a.exec();
}