QDataStream serialze & deserialize 'myclass' pointer

Taz742

hello all.
i have a problem serialize and deserialize datastream class pointer.

#include "mainwindow.h"
#include <QApplication>
#include "QDebug"
#include "QDataStream"
#include "QByteArray"

class myclass
{
    public:
        int x;
        int y;
        bool ok;
        QString message;
        myclass(){}
        myclass(int _x, int _y, bool _ok, QString _str) {
            this->x = _x;
            this->y = _y;
            this->ok = _ok;
            this->message = _str;
        }
};

void print(myclass *cls) {
    qDebug() << "answer: " << cls->x << cls->y >> cls->ok >> cls->message;
}

QDataStream & operator << (QDataStream &stream, const myclass *cls) {
    stream << static_cast<qint32>(cls->x) << static_cast<qint32>(cls->y) << cls->ok << cls->message;

    return stream;
}

QDataStream & operator >> (QDataStream &stream, myclass * cls) {
    qint32 tmpint;
    stream >> tmpint; cls->x = tmpint; //crash this line
    stream >> tmpint; cls->y = tmpint;

    return stream >> cls->ok >> cls->message;
}

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

//    MainWindow w;

//    w.show();

    QByteArray buff;
    QDataStream in(&buff, QIODevice::ReadWrite);
    in.setVersion(QDataStream::Qt_5_5);

    QMap<int, QVector<myclass*> > mp;

    mp[1].push_back(new myclass(1, 3, 0, "foo"));
    mp[2].push_back(new myclass(351, 5, 0, "bar"));

    in << mp;

    QDataStream out(&buff, QIODevice::ReadWrite);
    out.setVersion(QDataStream::Qt_5_5);

    QMap<int, QVector<myclass*> > mp1;
    QMap<int, QVector<myclass*> > ::iterator it;

    out >> mp1;

    for (it = mp1.begin(); it != mp1.end(); it++) {
        foreach (myclass *pr, mp1[it.key()]) {
            print(pr);
        }
    }

    return a.exec();
}

I wonder why so?
can you help me and fixed this problem?

If I do not use a pointer everything is fine.

bludger

Hi,

Your main issue is that the pointer passed to your stream operator is uninitialized.
Thereby the stream operator should have another signature:

QDataStream& operator>>(QDataStream& in, myclasss *& obj);

Note that the second parameter is a reference to a pointer. We need this in order to do the following:

QDataStream& operator>>(QDataStream& in, myclass*& obj) {
  obj = new myclass(); // pointer now correctly initialized 
  in >> obj->property;
  return in;
}

This should fix it.

Taz742

@bludger hm... i am stupid? :d
many thank friend, its fixed :)

VRonin

You are leaking memory like a bandit here.

QList<myclass> here instead of QVector<myclass*> is as efficient, less prone to memory leaks and doesn't require you to hack operator>> and operator<< for pointers type

Taz742

@VRonin waitttt. If I use QList, I will not have to teach DataStream how to arrange my class?

VRonin

yes but you wouldn't have to hack your way through it. You'd implement QDataStream & operator << (QDataStream &stream, const myclass& cls) and QDataStream & operator >> (QDataStream &stream, myclass& cls)
QList doesn't require a copy of the elements when it grows in size

Taz742

@VRonin I still use std :: vector <T> when I write programmatic tasks.
It's so deeply in my subconscious that I'm not trying to see what QList gives me better than QVector.

VRonin

you can imagine both QVector<T>(n) and std::vector<T>(n) as wrappers around T* vec = new T[n] while QList<T>(n) can be imagined as a wrapper around T** vec=new T*[n]; for(int i=0;i<n;++i) vec[i] = new T;

Now imagine inserting an item in the middle in those 2 cases.

That's why the docs suggests using QVector for types that are Q_MOVABLE_TYPE (the name can be misleading, see Q_DECLARE_TYPEINFO) and QList for the others

QVector<myclass*> containing heap allocated objects that QVector (should) own is, in practice, the same as QList<myclass>

Taz742

@VRonin Do you mean this?

       if (query.exec()) {
            QList<Contact> *_list = new QList<Contact>();
            while (query.next()) {
                _list->push_back(Contact(query.value("UID").toInt(),
                                         query.value("USERNAME").toString(),
                                         query.value("MOBILE").toString(),
                                         )
                                 );
            }

            qDebug() << _list->size();

            QByteArray bytes;
            QDataStream stream(&bytes, QIODevice::WriteOnly);
            stream << sSelecAllContacts << _list;
            globalall->modify(bytes);
            socket->write(bytes);
        }

I have just one pointer now?

kshegunov

@Taz742 said in QDataStream serialze & deserialize 'myclass' pointer:

@VRonin Do you mean this?

No. He means this:

QList<Contact> _list;
while (query.next()) {
    _list.push_back(Contact(query.value("UID").toInt(),
        query.value("USERNAME").toString(),
        query.value("MOBILE").toString(),
    ));
}

There is no gain at all in creating a Qt container in the heap.

Taz742

@kshegunov
Well, let's consider this case.
What I wrote this is the server side.

When I get it to the client side, if I get the same kind of list and get the value from it.
for example:

    QList<faf> list;

    list.push_back(faf(2, 13));
    list.push_back(faf(15, 23));
    list.push_back(faf(30, 46));

    faf test = list[0];
    test.x = test.x * 2;
    test.y = test.y * 2;

    for (int i = 0; i < list.size(); i++) {
        qDebug() << list[i].x << list[i].y; //Prints the same values
    }

If I want the object to change in the list.
Is it right?

    QList<faf> list;

    list.push_back(faf(2, 13));
    list.push_back(faf(15, 23));
    list.push_back(faf(30, 46));

    faf *test = &list[0];
    test->x = test->x * 2;
    test->y = test->y * 2;

    for (int i = 0; i < list.size(); i++) {
        qDebug() << list[i].x << list[i].y; //list[0].x = 4 and list[0].y = 46;
    }

kshegunov

@Taz742 said in QDataStream serialze & deserialize 'myclass' pointer:

// Prints the same values

Of course it does, you're copying the object that's stored in the list and modifying the copy.

If I want the object to change in the list.

Why convert to pointers? Just use references:

faf & test = list[0];
test.x *= 2;
test.y *= 2;

Taz742

@kshegunov good :))

Now there are new problems.
Recently everything was good.
I do not know what happened to me or why.

alt text

C:\Users\User\Desktop\tazsmsorigin\enumeration.h:69: error: no match for 'operator>>' (operand types are 'QDataStream' and 'qint32 {aka int}')
     stream >> tempint; _class.UID = tempint;
            ^
C:\Users\User\Desktop\tazsmsorigin\enumeration.h:50: error: ambiguous overload for 'operator<<' (operand types are 'QDataStream' and 'int')
     stream  << static_cast<qint32>(_class.UID)
             ^
C:\Users\User\Desktop\tazsmsorigin\enumeration.h:46: error: no match for 'operator>>' (operand types are 'QDataStream' and 'bool')
     return stream >> _class.TChecked >> _class.Message;
                   ^

kshegunov

Did you forget to include the <QDataStream> header?

Taz742

@kshegunov no. I have

kshegunov

Then you need to follow the compiler errors, it has given you exact directions where the errors are:
C:\Users\User\Desktop\tazsmsorigin\enumeration.h @ line 69

error: no match for 'operator>>' (operand types are 'QDataStream' and 'qint32 {aka int}')

I'm pretty sure this comes from not including the header. Also there's something amiss, it should be QDataStream & not QDataStream. Please post what's on line 69 in enumeration.h.

Taz742

@kshegunov
Yes the library was nat included, but I had it in globaldefines.h file.
He has caused a redifination proxy, QDataStream also has been described in MySocket.h file.

kshegunov

@Taz742 said in QDataStream serialze & deserialize 'myclass' pointer:

He has caused a redifination proxy, QDataStream also has been described in MySocket.h file.

I don't follow.

Taz742

@kshegunov I had code again mysocket.h, I taught at different places how to deal with my classes.

Taz742

@kshegunov @VRonin
How to handle QDataStream to my classes, this are stored in one 'header' file.
It's uncomfortable for me because I have many issues.
I learnt to my classes QDataStream >> and << operators.

For Example:

#ifndef POINT3D_H
#define POINT3D_H

#include "QObject"
#include "QDataStream"

class Point3D
{
public:
    Point3D();
    int x;
    int y;
    int z;

    Point3D(int _x, int _y, int _z) {
        this->x = _x;
        this->y = _y;
        this->z = _z;
    }

    friend QDataStream & operator << (QDataStream &stream, const Point3D &obj);
    friend QDataStream & operator >> (QDataStream &stream, Point3D &obj);
};

Q_DECLARE_TYPEINFO(Point3D, Q_MOVABLE_TYPE);

#endif // POINT3D_H

#include "point3d.h"

Point3D::Point3D()
{

}

QDataStream & operator << (QDataStream &stream, const Point3D &obj) {
    stream << static_cast<qint32>(obj.x) << static_cast<qint32>(obj.y) << static_cast<qint32>(obj.z);
    return stream;
}

QDataStream & operator >> (QDataStream &stream, Point3D &obj) {
    qint32 tempint;
    stream >> tempint; obj.x = static_cast<int>(tempint);
    stream >> tempint; obj.y = static_cast<int>(tempint);
    stream >> tempint; obj.z = static_cast<int>(tempint);

    return stream;
}

I want to be sure that this will work from anywhere. Can you confirm it?