PlEASE HELP: Hot To Use Byte Array, data stream

[ChrisW67]

The QDataStream writes enough information to reconstruct the item being written. When you write a byte, short, or int you get exactly 1, 2, or 4 bytes. Strings are written with an int indicating the length of the following string, in my example this is 12 bytes (6 x 2bytes per Unicode character). If you want single byte chars you should convert the QString to a char *, but you will still get the leading int indicating size.

QDataStream data(&arr,QIODevice::ReadWrite);
data.setVersion(QDataStream::Qt_4_6);
data<< quint16(0xBEEF) <<quint8('S');
data<< message.toAscii();
data<<(quint8('L'));
qDebug() << arr.toHex();
data.device()->seek(0);
data << quint16(arr.size() - sizeof(quint16));
qDebug() << arr.toHex();
data.device()->seek(0);
 
...
 
"beef53000000064142434445464c" 
"000c53000000064142434445464c"

QDataStream data(&arr,QIODevice::ReadWrite);
data.setVersion(QDataStream::Qt_4_6);
data<< quint16(0xBEEF) <<quint8('S');
data<< message.toAscii();
data<<(quint8('L'));
qDebug() << arr.toHex();
data.device()->seek(0);
data << quint16(arr.size() - sizeof(quint16));
qDebug() << arr.toHex();
data.device()->seek(0);

...

"beef53000000064142434445464c" 
"000c53000000064142434445464c"

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If you want absolute control of the bytes in the stream you probably don't want QDataStream; look into QBuffer and QByteArray