Serializing QHash to a QByteArray

[PeterThePuter]

Hey all,

I am having some trouble serializing a QHash. Following this snippit I attempted this:

#include <QtCore/QCoreApplication>
#include <QHash>
#include <QVariant>
#include <QDebug>
 
int main(int argc, char *argv[])
{
 
    QHash<QString,QVariant> hash;
    hash.insert("Key1",1);
    hash.insert("Key2","thing2");
 
    QByteArray ba;
    QDataStream ds(&ba, QIODevice::WriteOnly);
    ds << hash;
    qDebug() << ds;
 
}

#include <QtCore/QCoreApplication>
#include <QHash>
#include <QVariant>
#include <QDebug>

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

    QHash<QString,QVariant> hash;
    hash.insert("Key1",1);
    hash.insert("Key2","thing2");

    QByteArray ba;
    QDataStream ds(&ba, QIODevice::WriteOnly);
    ds << hash;
    qDebug() << ds;

}

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However, when I run it, qDebug() spits this out:

QIODevice::read: WriteOnly device
QIODevice::read: WriteOnly device
QIODevice::read: WriteOnly device
QVariant(, )

QIODevice::read: WriteOnly device
QIODevice::read: WriteOnly device
QIODevice::read: WriteOnly device
QVariant(, )

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What am I doing wrong?

Thanks!
-J

[franz]

Did you read your code? ds is defined as WriteOnly. You are then trying to output it to qDebug(). You cannot do that. One could even wonder how you would expect it to be output to qDebug()...

[PeterThePuter]

**Facepalm** Thanks!

the QByteArray ba is still empty however:

qDebug() << ba.isEmpty()

qDebug() << ba.isEmpty()

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gives true.

[wysota]

Maybe the data isn't flushed to the byte array yet? See if this works:

#include <QtCore/QCoreApplication>
#include <QHash>
#include <QVariant>
#include <QDebug>
 
int main(int argc, char *argv[])
{
 
    QHash<QString,QVariant> hash;
    hash.insert("Key1",1);
    hash.insert("Key2","thing2");
 
    QByteArray ba;
    {
        QDataStream ds(&ba, QIODevice::WriteOnly);
        ds << hash;
    } // here the stream gets destroyed so it has to flush whatever it caches
    qDebug() << ba;
}

#include <QtCore/QCoreApplication>
#include <QHash>
#include <QVariant>
#include <QDebug>

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

    QHash<QString,QVariant> hash;
    hash.insert("Key1",1);
    hash.insert("Key2","thing2");

    QByteArray ba;
    {
        QDataStream ds(&ba, QIODevice::WriteOnly);
        ds << hash;
    } // here the stream gets destroyed so it has to flush whatever it caches
    qDebug() << ba;
}

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