Save QMap with structure to file.

[Xandareva]

Hello,
I am new user Qt and I have got problem. So, I don't know how to save QMap with structure to file. I will show code.

void Test::saveMap() {
    QString fileName = QFileDialog::getSaveFileName(this, trUtf8("Save map to file"), "", trUtf8("Map (*.ttx);;All files (*)"));
    if (fileName.isEmpty())
        return;
    else {
        QFile file(fileName);
        if (!file.open(QIODevice::WriteOnly)) {
            QMessageBox::information(this, trUtf8("Can't to open file."), file.errorString());
            return;
        }
        QDataStream out(&file);
        out.setVersion(QDataStream::Qt_4_6);
        out << map;
    }
}

void Test::saveMap() {
    QString fileName = QFileDialog::getSaveFileName(this, trUtf8("Save map to file"), "", trUtf8("Map (*.ttx);;All files (*)"));
    if (fileName.isEmpty())
        return;
    else {
        QFile file(fileName);
        if (!file.open(QIODevice::WriteOnly)) {
            QMessageBox::information(this, trUtf8("Can't to open file."), file.errorString());
            return;
        }
        QDataStream out(&file);
        out.setVersion(QDataStream::Qt_4_6);
        out << map;
    }
}

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struct DataMap {
    QString name;
    QString name1;
    QString name2;
};
 
...
 
QMap<QString, DataMap> map;

struct DataMap {
    QString name;
    QString name1;
    QString name2;
};

...

QMap<QString, DataMap> map;

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QMap is declared as private - it is all ok. If I save QMap without structure (declaration: QMap<QString, QString> map) all is ok, but if I save QMap with structure DataMap, I have got a lot of errors. How does it fix? How to save QMap with structure to file?

Thanks.

Goodbye.

[Lykurg]

Hi,

see qRegisterMetaTypeStreamOperators and Q_DECLARE_METATYPE in addition.

[Tanuki-no Torigava]

An alternative way is to use QSettings.

[Danilo]

I have the same problem!!!!!!! I've read the proposed documentation but i always have the error....

Has anyone solved it?

Here is my code:

// Mapping between String and MyStruct
QMap<QString, MyStruct> mydata;

-------
-------
-------

QDataStream out(&file);
out.setVersion(QDataStream::Qt_4_8);
out << mydata;




I get this error (also in input mode....):
/usr/include/qt4/QtCore/qdatastream.h:429: error: no match for 'operator<<' in 'operator<<((* & out), (* & it.QMap<Key, T>::const_iterator::key [with Key = QString, ......

Can anyone help me?

Thanks

[wysota]

Did you implement the << operator for your struct?

[Danilo]

No, i have not overloaded the << operator...... do you think is it necessary??

Because i've read this reference (http://qt-project.org/doc/qt-4.8/qsettings.html) but i have not understood the linking with my problem!
So sorry i'm a beginner

Best

[wysota]

No, i have not overloaded the << operator...... do you think is it necessary??

Yes, it is necessary.

And I don't see what QSettings has anything to do with your situation since you are not using it but rather QDataStream.

[Danilo]

Ok, finally i've understand......
So, i must overload the operator <<, in this way defined:

template <class Key, class T>
Q_OUTOFLINE_TEMPLATE QDataStream &operator<<(QDataStream &out, const QMap<Key, T> &map)
{
out << quint32(map.size());
typename QMap<Key, T>::ConstIterator it = map.end();
typename QMap<Key, T>::ConstIterator begin = map.begin();
while (it != begin) {
--it;
out << it.key() << it.value();
}
return out;
}

substituting it with:

template <class Key, class T>
Q_OUTOFLINE_TEMPLATE QDataStream &operator<<(QDataStream &out, const QMap<Key, T> &map)
{
out << quint32(map.size());
typename QMap<Key, T>::ConstIterator it = map.end();
typename QMap<Key, T>::ConstIterator begin = map.begin();
while (it != begin) {
--it;
out << it.key() << it.value().FIELD_1_of_MyStruct << it.value().FIELD_2_of_MyStruct ......
}
return out;
}

Is it correct?

[wysota]

You only need

QDataStream& operator<<(const MyStruct &);

QDataStream& operator<<(const MyStruct &);

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