QDatastream operator>> for QList<Class*>

Question

So i have overloaded the >> and << operators for QDatastream for custom classes. I made 2 versions of each; one for the base object and one for a pointer of the object. So far all versions of the operators work with one exception. The pointer read operator reads the correct data but it is not saved correctly in a QList<*>.

Here's some example code.

QDataStream & operator <<(QDataStream &dataStream, const Faction &rhs)
{
    return rhs.write(dataStream);
}

QDataStream & operator >>(QDataStream &dataStream, Faction &rhs)
{
    return rhs.read(dataStream);
}

QDataStream & operator <<(QDataStream &dataStream, const Faction *rhs)
{
    return rhs->write(dataStream);
}

QDataStream & operator >>(QDataStream &dataStream, Faction *rhs)
{
    rhs = new Faction();
    return rhs->read(dataStream);
}

QDataStream & Faction::read(QDataStream &dataStream)
{
    QString tag;
    dataStream >> tag;

    QString classTag = QString(typeid(this).name());
    getTypeName(&classTag);
    if (tag == classTag + "Start")
    {
        while (tag != classTag + "End")
        {
            if (tag == "name")
            {
                dataStream >> name;                  // The name of the faction.
            }
            else if (tag == "buildings")
            {
                dataStream >> buildings;             // The buildings of the Faction.
            }
            else if (tag == "units")
            {
                dataStream >> units;                 // The units of the Faction.
            }
            else if (tag == "upgrades")
            {
                dataStream >> upgrades;              // The upgrades of the Faction.
            }
            else if (tag == "startBuildings")
            {
                dataStream >> startBuildings;    // The list of buildings when starting a game.
            }
            else if (tag == "startUnits")
            {
                dataStream >> startUnits;        // The list of units when starting a game.
            }
            else if (tag == "startUpgrades")
            {
                dataStream >> startUpgrades;     // The list of upgrades when starting a game.
            }

            // Reading the next tag.
            dataStream >> tag;
        }
    }
    return dataStream;
}

QDataStream & Faction::write(QDataStream &dataStream) const
{
    QString classTag = QString(typeid(this).name());
    getTypeName(&classTag);
    dataStream << QString(classTag + "Start");

    dataStream << QString("name");
    dataStream << name;                           // The name of the faction.
    dataStream << QString("buildings");
    dataStream << buildings;             // The buildings of the Faction.
    dataStream << QString("units");
    dataStream << units;                 // The units of the Faction.
    dataStream << QString("upgrades");
    dataStream << upgrades;              // The upgrades of the Faction.
    dataStream << QString("startBuildings");
    dataStream << startBuildings;    // The list of buildings when starting a game.
    dataStream << QString("startUnits");
    dataStream << startUnits;        // The list of units when starting a game.
    dataStream << QString("startUpgrades");
    dataStream << startUpgrades;     // The list of upgrades when starting a game.

    dataStream << QString(classTag + "End");

    return dataStream;
}

Faction.h

    #ifndef FACTION_H
    #define FACTION_H

    #include <JECUtils.h>

    #include <Unit.h>
    #include <UnitBase.h>

    class Faction
    {
    public:
        explicit Faction();
        explicit Faction(const QString& name);
        Faction(const Faction& faction);

        Faction& operator=(const Faction& rhs);
        bool operator==(const Faction& rhs) const;
        bool operator!=(const Faction& rhs) const;

        friend QDataStream &operator<<(QDataStream &dataStream, const Faction& rhs);
        friend QDataStream &operator>>(QDataStream &dataStream, Faction& rhs);
        friend QDataStream &operator<<(QDataStream &dataStream, const Faction* rhs);
        friend QDataStream &operator>>(QDataStream &dataStream, Faction* rhs);

        void addBuilding(UnitBase* building);
        void addUnit(UnitBase* unit);
        void addUpgrade(UnitBase* upgrade);

        const QString& getName() const;
        const UnitBase* getBuilding(const int& index) const;
        const QList<UnitBase*>& getBuildings() const;
        const UnitBase* getUnit(const int& index) const;
        const QList<UnitBase*>& getUnits() const;
        const UnitBase* getUpgrade(const int& index) const;
        const QList<UnitBase*>& getUpgrades() const;
        const QList<QList<Unit*> >* getStartUnits() const;
        const QList<QList<Unit*> >* getStartBuildings() const;
        const QList<QList<Unit*> >* getStartUpgrades() const;

        void initialize(const QStringList& globalActions);

        void removeAllBuilding();
        void removeAllUnit();
        void removeAllUpgrade();
        void removeBuilding(const int& index);
        void removeUnit(const int& index);
        void removeUpgrade(const int& index);

        void setStartUp(const QStringList& names, const QList<int>& quantities);

    protected:
        QDataStream& read(QDataStream &dataStream);
        QDataStream& write(QDataStream &dataStream) const;

    private:
        QString name;                           // The name of the faction.
        QList<UnitBase*> buildings;             // The buildings of the Faction.
        QList<UnitBase*> units;                 // The units of the Faction.
        QList<UnitBase*> upgrades;              // The upgrades of the Faction.
        QList<QList<Unit*> > startBuildings;    // The list of buildings when starting a game.
    QList<QList<Unit*> > startUnits;        // The list of units when starting a game.
    QList<QList<Unit*> > startUpgrades;     // The list of upgrades when starting a game.
};

#endif // FACTION_H

So in this particular example i have a QList. When the code

dataStream >> factions

is ran, the entire QList of Faction* is supposed to be read in. However i get garbage.

QDataStream & operator >>(QDataStream &dataStream, Faction *rhs)
{
    rhs = new Faction();
    return rhs->read(dataStream); <---- rhs will return good data.
}

rhs contains the correct data read in from the file. However, after the entire QList has been read, garbage values are in the QList.

Can anyone help me out?

Answer 1

The operator >> expects a reference as its second parameter, and you can have references to pointers too:

QDataStream & operator >>(QDataStream &dataStream, Faction *&rhs)
{
    rhs = new Faction();
    return rhs->read(dataStream);
}

Answer 2

Because you want to alter what rhs points to, you should pass a pointer to pointer as an argument to your operator.

Also, doing that, the changes to the pointer, will be reflected when the function returns.

QDataStream & operator >>(QDataStream &dataStream, Faction **rhs)
{
    *rhs = new Faction();
    return (*rhs)->read(dataStream); <---- rhs will return good data.
}