Converting qint8 to string

roboterprogrammer

hello,

i want to send an qint8 via tcpip, and for that, after the connection is etablished via the socket,
i want to use the
@
socket->write("GUISTATUS: \n");@
directive
and i want to add one qint8 variable, in which 8 independent informations are included, in each bit one.
how can i put it in the string?

it didnt work for me with QDataStream, i think because i didnt use a file.

Thanks for hinds and advices.

andre

QDataStream should work just fine. You could prepare your data like this:
@
//pseudo-code, brain to terminal
QByteArray data;
QDataStream s(&data);
s << "GUISTATUS\n";
s << myUint8Variable;
socket->write(data);
@

roboterprogrammer

hi,

thanks for the fast reply.

i tried

@ QByteArray data;
QDataStream s(&data);

    s << guistatus;
    s << "GUISTATUS\n";
    socke->write(data);@

and i get an error:

@C:\Dokumente und Einstellungen\loetrobo\Robbie20-build-desktop-Qt_4_8_0_for_Desktop_-_MinGW__Qt_SDK__Debug..\Desktop\Robbie20\robbie20.cpp:234: error: no matching function for call to 'QDataStream::QDataStream(QByteArray*)'@

andre

According to the docs for [[doc:QDataStream]], there is a constructor for a QDataStream that takes a QByteArray pointer and a flag to indicate the opening mode, and there is a constructor that takes a QByteArray reference. The documentation explains why you want the first one when writing to the byte array.

That's why I said "pseudo-code, brain to terminal". You're supposed to interpret that as "this is the general idea, lookup the exact function names and signatures yourself in the documentation".

KA51O

This should solve the compiler error:

@
QDataStream s(&data, QIODevice::ReadWrite);
@

roboterprogrammer

hi, thanks thats what i tried

thats my code:
@ qint8 integ = 0b00001111;
QByteArray helparray = "GUISTATUS\n";
QByteArray data;
QDataStream s(&data, QIODevice::ReadWrite);
QString helpstring;

s << helparray;
s >> helpstring;
qDebug() << "helpstring: " << helpstring;@

i expected to get in my qdebug window, but the QString is totally empty.

@helpstring: "" @

where is my mistake?
i cant find it, didn't know this conversation is such a big deal.

andre

On line 8 of your code above, you start reading at the current position in the stream. That is: after what you just wrote.

Just use the write-only mode instead, and display your data bytearray directly with qDebug.

roboterprogrammer

hi,

ah okay. but when i do like this, i get an " QIODevice::read: WriteOnly device" advice.

@ qint8 integ = 0b00001111;
QByteArray helparray = "GUISTATUS";
QByteArray data;
QDataStream s(&data, QIODevice::WriteOnly);
QString helpstring;

s << integ <<" test";
qDebug() << "data: " << data;
s >> helpstring;

  qDebug() << "helpstring: " <<  helpstring; @

the output in the qdebug is not correct.
data: " -> incomplete
helpstring: "" -> empty

its important its a string i send, because then i can check if there are unwanted signs inside like /n i could remove manually.
i feel like qt put some of those with the << operator, so i keep full control.

andre

Hmmm.... Perhaps QDataStream isn't for you after all. I am sorry I suggested it. QDataStream does not only stream the raw data, but also some meta data (like the length of a QByteArray you stream in) if needed. You can circumvent that using QDataStream::writeBytes or QDataStream::writeRawBytes, but that defeats the point of using it in the first place, right?

Note that your warning is caused by your line 9 above. If you use a WriteOnly stream, you can't obviouly read from it. Also, streaming into a QString probably doesn't do what you expect it does... Instead, use one of the QString::from<Encoding>() methods to construct a string from a QByteArray.

Anyway, you can probably get rid of QDataStream completely, as it screws up your data in your case if you add a QByteArray. Instead, you could try this:

@
//again, untested code:
QByteArray data;
data += "GUISTATUS";
data.append( reinterpret_cast<char*>(&myUInt8Variable), 1 ); //Warning: no idea if this will work ok
qDebug() << "data:" << data;
@

Or, using QDataStream again, but only for the integer:
@
//again, untested code:
QByteArray data;
data += "GUISTATUS";
QDataStream s(&data, QIODevice::WriteOnly);
s << myUInt8Variable;
qDebug() << "data:" << data;
@

Neutron Stein

did you try QString().setNum(myUInt8Variable) to convert ?

andre

[quote author="Neutron Stein" date="1342534822"]did you try QString().setNum(myUInt8Variable) to convert ?[/quote]

He was looking for a QByteArray (to send over a TCP socket). Converting to a string does not help for that.

Neutron Stein

isn't the topic?converting from quint8 to string?

andre

[quote author="Neutron Stein" date="1342535272"]isn't the topic?converting from quint8 to string?[/quote]

Not really:
[quote author="roboterprogrammer" date="1342524761"]i want to send an qint8 via tcpip, and for that, after the connection is etablished via the socket,
i want to use the
@
socket->write("GUISTATUS: \n");@
directive
and i want to add one qint8 variable, in which 8 independent informations are included, in each bit one.[/quote]

You need to read more than just the subject header... And yes, I sometimes fail to do that as well.

Neutron Stein

I think this can help.
@
QByteArray paquet;
QDataStream data(&paquet,QIODevice::WriteOnly);
data << (quint8)0;
data << theStringToSend;
data.device()->seek(0);
data << (quint8)(paquet.size() - sizeof(quint8));
socket->write(paquet);
@

roboterprogrammer

hi,

solution 2 works now, so i can send data (changes that operator made) to gui,
but its not nice.

if no better solution i will keep it like this.
the thing is:

with @s << myUInt8Variable;@

it writes it to the first postiton of data.

so in qdebug instead of GUISTATUSX i get XUISTATUS

how can i put it on the end?

roboterprogrammer

wow so many replys i will read them, and try the new stuff out.

thanks

Neutron Stein

sorry I sent the wrong code.but it might be something like that. there i put the packet size at the beginning of the packet to be sent.i think you just need to put there what you want to send.
Sorry for mistakes i'm newbie