Server-client receiving and sending problem using QtcpSocket for console application

[Mijaz]

I am sending string value from sever to the client which is ok, but I need to write from server to client an integer value which will be displayed on QlcdNumber on client-side. Which is displaying 0 there.

[jsulm]

@Mijaz said in Server-client receiving and sending problem using QtcpSocket for console application:

but I need to write from server to client an integer value

So, does your server send an int? What does ok contain after toInt()? Did you check what readAll() returns? Also, did you check how many bytes readAll() returns?

[Mijaz]

@jsulm I implement your above code its still giving me 0 value on QlcdNumber and in qDebug also.

[Mijaz]

@jsulm from server-side I am not able to send the data in integer I am sending it therefrom QByteArray data; which is socket->write(data); and receiving it on client-side as "\u027" which is not displayed on QlcdNumber. I need the solution for this how I can display it on QlcdNumber.

[jsulm]

@Mijaz This is your code for sending int, right?

data[0] = (uchar) (0x000000ff & current_temp);
data[1] = (uchar) ((0x0000ff00 & current_temp) >> 8);
data[2] = (uchar) ((0x00ff0000 & current_temp) >> 16);
data[3] = (uchar) ((0xff000000 & current_temp) >> 24);

Don't you think you need to do same on the receiver side?
But actually it would be way easier to use https://doc.qt.io/qt-5/qdatastream.html on both sides.

[Mijaz]

@jsulm I did QFile code on both side but I am getting an error QIODevice::read (QFile, "file.dat"): device not open on the receiver side. I am thinking on QTcpSocket how your QFile will work?

[jsulm]

@Mijaz said in Server-client receiving and sending problem using QtcpSocket for console application:

I am thinking on QTcpSocket how your QFile will

Which QFile?!
I never suggested to use any QFile!
QDataStream also works with QByteArray as you can easily see from its documentation...

[KroMignon]

@Mijaz said in Server-client receiving and sending problem using QtcpSocket for console application:

did QFile code on both side but I am getting an error QIODevice::read (QFile, "file.dat"): device not open on the receiver side. I am thinking on QTcpSocket how your QFile will work?

You are going in wrong direction!
Think simple!

Qt has many helper classes.
If I right understand your use case:

• you have an external application which send an integer value per TCP.
• first you said value is send as string, which means for me a text. Decimal value 1 is send as string "1".
• then you said value is send as "raw data", which mean for me a binary. Decimal value 1 is send as 4 bytes ("\x00\x00\x00\x01" or "\x01\x00\x00\x00" depending on endiannes).

To read as text value and convert it back to decimal:

QString str=m_client1->readAll();
bool ok;
int value = str.toInt(&ok);
if(!ok)
  qDebug() << "Could not read integer value";
else
  qDebug() << "Recieved" << value;

To read as binary value and convert it back to decimal:

QByterArray b=m_client1->readAll();
QDataStream stream(b);
// to change byte order (endianess)
// stream.setByteOrder(QDataStream::LittleEndian);
int value;
stream >> value;
if(stream.status() != QDataStream::Ok)
  qDebug() << "Could not read integer value";
else
  qDebug() << "Recieved" << value;

[Mijaz]

@KroMignon Thanks for your excellent approach my value on QlcdNumber displayed successfully but not showing me the actual value current_temp from server-side it is displaying 385875968 instead of 23.

[JonB]

@Mijaz
How should anyone answer this? What is the server actually sending? Where in the stream does it appear? How are you reading it (you might check byte-by-byte initially that you get the right bytes)? How do you convert it to a number (e.g. is your bad number an endian-ness issue)?

[jsulm]

@JonB This is what is sent:

data[0] = (uchar) (0x000000ff & current_temp);
data[1] = (uchar) ((0x0000ff00 & current_temp) >> 8);
data[2] = (uchar) ((0x00ff0000 & current_temp) >> 16);
data[3] = (uchar) ((0xff000000 & current_temp) >> 24);

And as I already wrote before this needs to be considered on the receiver side, but did not hear any feedback...

@Mijaz If you use QDataStream on receiver side you also have to use it on the sender side!

[Mijaz]

@JonB server is actually sending analog temperature sensor value in an integer which is continuously changing via QTcpSocket to client where it is displayed on QlcdNumber.

[Mijaz]

@jsulm Let me try to use QDataStream on the sender side

[JonB]

@jsulm
Ah I see! has anyone checked whether

it is displaying 385875968 instead of 23.

385875968 might be 23 in reverse bytes order (I don't know if it is)?

[Mijaz]

@JonB thanks it's working now.