Problem with gbinary files, and QVector

[Loc888]

@mrjj Back to that QFile for one moment, i have to inherit that QDataStream, and overload the operators?

[jsulm]

@Loc888 No, you just implement << and >> operators for your own data types.
See documentation: http://doc.qt.io/qt-5/qdatastream.html#
You need:

QDataStream &operator<<(QDataStream &, const YOUR_TYPE &);
QDataStream &operator>>(QDataStream &, YOUR_TYPE &);

You don't have to do it for Qt types like QVector.

[Loc888]

@jsulm Ok, i took a look, and it says

"In addition to the overloaded stream operators documented here, any Qt classes that you might want to serialize to a QDataStream will have appropriate stream operators declared as non-member of the class:"

So i have to do that, outside the class, but how to use it then? If i crate a object, then how to use that overloaded operators?

[mrjj]

@Loc888 said in Problem with gbinary files, and QVector:

So i have to do that, outside the class, but how to use it then? If i crate a object, then how to use that overloaded operators?

Hi
That is the easy part.
Simply try it and see

QFile file("file.dat");
file.open(QIODevice::WriteOnly);
QDataStream out(&file);
out << *yourclassptr;
(note the *)
if Qt can find an << for a type, it will simply use it.

That way, you can << anything you like.

[Loc888]

@mrjj Ok, i try. SO i have to do a class, put there thise operators, and then use:

out << *new_class ?

[mrjj]

@Loc888
Yes and the reason for the * in from of object pointer is that the header says
(QDataStream &, const YOUR_TYPE &); << reference

so if you give it the pointer without *, it
will save/stream the address of the object as it then matches << for int instead.
so say always use * when you have a pointer to an object with <<

[mrjj]

Hi
Just to be sure
can you show your
QDataStream &operator<<(QDataStream &, const YOUR_Class &);
implementation.
(not the .h declaration) but the actual body of it.

[Loc888]

@mrjj In the QDataStream Class it looks like that, so i guess i am gonna use this template, except i am gonna use a custom data:

inline QDataStream &QDataStream::operator<<(quint16 i)
{ return *this << qint16(i); }

[mrjj]

Hi
Here is small sample.

--in the .H file--
class MyClass
{
public:
    int value = 6;
    QString name = "test";
};

QDataStream &operator<<(QDataStream &out, const MyClass &);
QDataStream &operator>>(QDataStream &in, MyClass &);

-----------
--in the .CPP file--
QDataStream &operator<<(QDataStream &out, const MyClass &classRef) {
return out << classRef.value <<  classRef.name; // save each member of your class
}

QDataStream &operator>>(QDataStream &in,  MyClass &classRef){
return in >> classRef.value >>  classRef.name; // read in IN SAME order
}

------------------------------
//--test of saving--
   {
        QFile file("e:/file.dat");
        file.open(QIODevice::WriteOnly);
        QDataStream out(&file);
        MyClass *ptr = new MyClass;
        out << *ptr;
    }
//--test of loading--
    {
        QFile file("e:/file.dat");
        file.open(QIODevice::ReadOnly);
        QDataStream in(&file);
        MyClass *otherptr = new MyClass;
        in >> *otherptr;      
    }

[Loc888]

@mrjj Something weird is happening, i declared those operators in a header file, then include it, and it's working, if i use that MyClass pointer, then i get the error..

[mrjj]

@Loc888
What error?

[Loc888]

@mrjj Nope, it's ok... I just typed the wrong object type. It's working finnaly. Thanks
everybody for help.

[mrjj]

@Loc888
Good work. :)
please mark as solved then.

[Loc888]

@mrjj It's solved, but i don't wanna close it, maybe somebody will need help with that STD stuff, i leave it behind for now, because this motheod is cleaner and faster.

[jsulm]

@Loc888 Please close. If somebody has a problem/question he/she can open a new thread. Your problem is solved, right?