Qt: Iterate a QMap (https://stackoverflow.com/a/55187379/7670262)

qt_qmap_iteration.cpp

// https://stackoverflow.com/a/55187379/7670262

#include <QDebug>
#include <QMap>
#include <QMapIterator>
#include <QString>

int main()
{
    using InnerMap = QMap<int, QString>;
    using OuterMap = QMap<int, InnerMap>;

    const OuterMap outerMap
    {
        { 1, {{ 11, "a" }, { 12, "aa" }} },
        { 2, {{ 22, "b" }, { 21, "bb" }} },
        { 3, {{ 22, "c" }} }
    };

    qDebug() << "--- foreach (QMap) ---";

    foreach ( const auto& outerKey, outerMap.keys() )
    {
        qDebug() << outerKey;

        const auto& innerMap = outerMap[ outerKey ];
        foreach ( const auto& innerKey, innerMap.keys() )
        {
            const auto& innerValue = innerMap[ innerKey ];
            qDebug() << "\t{" << innerKey << "," << innerValue << "}";
        }
    }

    qDebug() << "\n--- range-for (QMap -> std::map) ---";

    const auto& m1 = outerMap.toStdMap();
    for ( const auto& p1 : m1 )
    {
        qDebug() << p1.first;

        const auto& m2 = p1.second.toStdMap();
        for ( const auto& p2 : m2 )
        {
            qDebug() << "\t{" << p2.first << "," << p2.second << "}";
        }
    }

    qDebug() << "\n--- while (QMapIterator) ---";

    QMapIterator<int, InnerMap> outerIt{ outerMap };
    while ( outerIt.hasNext() )
    {
        outerIt.next();
        qDebug() << outerIt.key();

        QMapIterator<int, QString> innerIt{ outerIt.value() };
        while ( innerIt.hasNext() )
        {
            innerIt.next();
            qDebug() << "\t{" << innerIt.key() << "," << innerIt.value() << "}";
        }
    }

    return 0;
}

/*

// OUTPUT:

--- foreach (QMap) ---
1
        { 11 , "a" }
        { 12 , "aa" }
2
        { 21 , "bb" }
        { 22 , "b" }
3
        { 22 , "c" }

--- range-for (QMap -> std::map) ---
1
        { 11 , "a" }
        { 12 , "aa" }
2
        { 21 , "bb" }
        { 22 , "b" }
3
        { 22 , "c" }

--- while (QMapIterator) ---
1
        { 11 , "a" }
        { 12 , "aa" }
2
        { 21 , "bb" }
        { 22 , "b" }
3
        { 22 , "c" }

*/