Qdatastream overloaded function from a readready slot

Sunfluxgames

I'm a little bit confused in how to use the Qdatastream operators or read and write data to a socket.

struct Science { int abby , int becky };

QDataStream &operator<<(QDataStream &stream, const Science &s) {
    stream << s.abby << s.becky;
    return stream;
}

QDataStream &operator<<(QDataStream &stream, Science &s) {
    stream >> s.abby >> s.becky;
    return stream;
}

how do i call these operators to fill in the data once i call my qdatastream from readready slot?

Anyone have a good full example of ready data from the socket then de-serialize it to a operator then serialize it back to the write socket.

VRonin

// serialise

QDataStream stream(iodevice);
Science variable;
stream << variable;

// deserialise

QDataStream stream(iodevice);
Science variable;
stream >> variable;

Sunfluxgames

void ServerThread::readyRead()
{
     QDataStream in(socket);
      Science variable;

     in.startTransaction();
     in >> variable;
    if(in.commitTransaction())
    {
      // All data necessary was received
   }
// proccess data here
}

What do i do about padding? how can i make it dynamic to de-serialize base on whatever structure was received.

Christian Ehrlicher

@Sunfluxgames said in Qdatastream overloaded function from a readready slot:

What do i do about padding?

What do you mean with this? QDataStream is writing the data in it's own format so why do you want to pad something?

how can i make it dynamic to de-serialize base on whatever structure was received.

You need to distinguish between the different structures by e.g. a type field.

Sunfluxgames

The receiving stream comes in a padding form. The client expects it to be padded.

Other than align the structure to be padded i guess?

JonB

@Sunfluxgames
If @Christian-Ehrlicher is correct when he says

QDataStream is writing the data in it's own format

and you seem to want to read from/write to an external non-Qt source (right?) with its own "padding"/format, then I would not think QDataStream can be used? It sounds more like you need to do your own char-by-char reading/writing of this Science class? Similarly, how are your ints to be passed between client & server?

Sunfluxgames

Yes it is a non-QT source. My original source does a custom read/write without QDataStreams. I was just trying to see if I could use QDataStreams instead.

Only thing I can think of is once it enters the QDataStream is to strip the padding and use it like a normal QDataStream.

Build the reading Structure to fit the need of whatever type field I choose. Build the writing Structure to fit the needed size of whatever the non-QT source wants.

Something like this possible maybe?

typedef struct __atribute__((packed)) Science {
    quint32 abby;
    quint32 becky;
} Science;

Christian Ehrlicher

As @JonB already told you you can't use QDataStream for your task and have to write the decoding by your own.

mpergand

@Sunfluxgames said in Qdatastream overloaded function from a readready slot:

Something like this possible maybe?
typedef struct atribute((packed)) Science {
quint32 abby;
quint32 becky;
} Science;

Just have a try !

As an old C programmer, i like to fiddle around with bytes :)
Let's go:

struct __attribute__((packed)) Science
{
    quint8  a;
    quint16 b;
    quint8  c;
};

QByteArray arr=QByteArray::fromHex("01 01 04 0a");
QDataStream stream(arr);
qint16 b;
qint8 a,c;
stream>>a>>b>>c;

in the degugger i see:
arr "\001\001\004\n" QByteArray
a 1 qint8
b 260 qint16
c 10 qint8

So far so good.

and now with the struct;

QDataStream &operator>>(QDataStream &stream, Science &s) {
    stream >> s.a >> s.b>>s.c;
    return stream;
}

QByteArray arr=QByteArray::fromHex("01 01 04 0a");
QDataStream stream(arr);
Science sc;
stream>>sc;

arr "\001\001\004\n" QByteArray
sc @0x7fff5fbffb48 Science
a 1 quint8
b 260 quint16
c 10 quint8

Well, everything is ok.
The main question is that 100% sure/reliable ?
That's your own choice ;)
(note: the values are decoded in big endian)