How to use Q_DECLARE_METATYPE correctly with a custom class?

[Thomas Wrobel]

Background:
Ok, Ive started learning C++ / QT recently, but previous knowledge of Java and many other languages. I worked over the address book tutorial fairly easily, but wanted to adapt/expand it to make sure I got everything ok.
I did this by making a class (addressdata) to store various forms of address data rather then just name/address, then adapting the code to use this class in a QList rather then the QMap.
This worked fine, adjustments to the searching/finding functions were also fairly easy to do.

Problem:
However, I now need to learn how to save this data out to a file.
QDataStream wont take the QList< addressdata> as an input.

I found this page;
http://wiki.qtcentre.org/index.php?t..._types_with_Qt

Which seems to detail what I have to do...correct?

Only at the very first step of putting a "Q_DECLARE_METATYPE(Player);" at the end of my class code, I start getting a ;

(path)/../src/corelib/kernel/qmetatype.h:126: error: no matching function for call to `addressdata::addressdata()'

Any ideas how I'm supposed to implement this correctly?

My class code is;

#ifndef ADDRESSDATA_H
#define ADDRESSDATA_H
 
#include <QWidget>
#include <QMap>
 
 
class addressdata
{
 
 
public:
    addressdata(QString);
    void set(QString,int,int,int);    // function inputting the data
    int getX();
    int getY();
    int getZ();
    QString getAddress();
    QString getName();
    QString getXasText();
    QString getYasText();
    QString getZasText();
 
    void setAddress(QString);
    void setName(QString);
    void setX(int);
    void setY(int);
    void setZ(int);
 
    ~ addressdata();
 
private:
    int Xpos;      
    int Ypos;        
    int Zpos;       
QString address;
QString name;
 
};
 
Q_DECLARE_METATYPE(addressdata);
 
#endif // ADDRESSDATA_H

#ifndef ADDRESSDATA_H
#define ADDRESSDATA_H

#include <QWidget>
#include <QMap>


class addressdata
{


public:
    addressdata(QString);
    void set(QString,int,int,int);    // function inputting the data
    int getX();
    int getY();
    int getZ();
    QString getAddress();
    QString getName();
    QString getXasText();
    QString getYasText();
    QString getZasText();

    void setAddress(QString);
    void setName(QString);
    void setX(int);
    void setY(int);
    void setZ(int);

    ~ addressdata();

private:
    int Xpos;      
    int Ypos;        
    int Zpos;       
QString address;
QString name;

};

Q_DECLARE_METATYPE(addressdata);

#endif // ADDRESSDATA_H

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Thanks in advance for any help you can give me,
Cheers

[Grimlock]

You are missing a default constructor in your class implementatnion.
You may also need to add a copy constructor.

adressdata::addressdata()
: Xpos(0),      
Ypos(0),       
Zpos(0),       
address(""),
name("")
{}
adressdata::adressdata(const adressdata& other)
{
....
}

adressdata::addressdata()
: Xpos(0),      
Ypos(0),       
Zpos(0),       
address(""),
name("")
{}
adressdata::adressdata(const adressdata& other)
{
....
}

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[Grimlock]

Sorry double post

[Thomas Wrobel]

You are missing a default constructor in your class implementatnion.
You may also need to add a copy constructor.

adressdata::addressdata()
: Xpos(0),      
Ypos(0),       
Zpos(0),       
address(""),
name("")
{}
adressdata::adressdata(const adressdata& other)
{
....
}

adressdata::addressdata()
: Xpos(0),      
Ypos(0),       
Zpos(0),       
address(""),
name("")
{}
adressdata::adressdata(const adressdata& other)
{
....
}

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Ok, thanks that works

At least, I think so.
I'm now getting a "error: no match for 'operator<<' in 's << (+l)->QList<T>::at [with T = addressdata](i)'", which I assume means I havnt defined what that << operator should do.

I placed;

inline QDataStream& operator<<(QDataStream& out, const addressdata& data)
{
out << data.Xpos;
out << data.Ypos;
out << data.Zpos;
out << data.getName();
out << data.getAddress();

return out;
}
inline QDataStream& operator>>(QDataStream& in, addressdata& data)
{
in >> data.Xpos;
in >> data.Ypos;
in >> data.Zpos;
in >> data.getName();
in >> data.getAddress();
return in;
}

Into the class definition of addressdata.
This gives me this though;

`QDataStream& addressdata:perator<<(QDataStream&, const addressdata&)' must take exactly one argument

Seeing as I copyed the formatting from the wiki (with the two arguments), I'm assuming Ive played it in the wrong place? Should the inlines go here?

Cheers,
Thomas

[Grimlock]

Declare them outside of your class and befriend the operators or just remove the seckond parameter and try using this-> instedof data.

[wysota]

You don't need to declare the metatype for your class to be able to stream it to QDataStream.

[Thomas Wrobel]

Declare them outside of your class and befriend the operators

Not sure how to do befriending, let alone with operators.

friend void QDataStream::??(QDataStream); ?

or just remove the seckond parameter and try using this-> instedof data.

I tried changing it to;

inline QDataStream& operator<<(QDataStream& out)
{
    out << this->Xpos;
    out << this->Ypos;
    out << this->Zpos;
    out << this->name;
    out << this->address;
 
    return out;
}
inline QDataStream& operator>>(QDataStream& in)
{
    in >> this->Xpos;
    in >> this->Ypos;
    in >> this->Zpos;
    in >> this->name;
    in >> this->address;
 
    return in;
}

inline QDataStream& operator<<(QDataStream& out)
{
    out << this->Xpos;
    out << this->Ypos;
    out << this->Zpos;
    out << this->name;
    out << this->address;

    return out;
}
inline QDataStream& operator>>(QDataStream& in)
{
    in >> this->Xpos;
    in >> this->Ypos;
    in >> this->Zpos;
    in >> this->name;
    in >> this->address;

    return in;
}

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in addressdata.h, but I still got;

error: no match for 'operator<<' in 's << (+l)->QList<T>::at [with T = addressdata](i)


I'm probably doing something really basic wrong.

[Thomas Wrobel]

You don't need to declare the metatype for your class to be able to stream it to QDataStream.

Dont I?
What if I want to use my class with reading/witting to network connections, which is something I'll certainly want to learn how to do in future.

[wysota]

Dont I?

No. It's only for placing objects of your class as values of QVariant.

What if I want to use my class with reading/witting to network connections, which is something I'll certainly want to learn how to do in future.

You don't need Q_DECLARE_METATYPE. Just provide steaming operators to QDataStream if you want to use it.

[Thomas Wrobel]

Ok, so I just gota learn how to set up my streaming operators correctly, thanks

[squidge]

The QDebug Class Reference has a good example of how to setup streaming operators so you can add custom types to debug output. The same applies to other objects such as QDataStream.

[Thomas Wrobel]

Did you mean: http://doc.trolltech.com/4.5/qdebug.html ?

Because I was already attempting to use the examples here (see above);
http://wiki.qtcentre.org/index.php?t..._types_with_Qt
Which seem better.