how QDataStream and QByteArray related

[dognzhe]

I am not sure why every one has to use QDataStream with QByteArray ??
why???

please have a look the code

QBuffer buffer;
QImageWriter writer(&buffer, "PNG");
writer.write( randomImage() );
[COLOR="red"]QByteArray data;[/COLOR]
QDataStream stream( &data, QIODevice::WriteOnly );
stream << (quint32)buffer.data().size();
data.append( buffer.data() );
socket.write( data );

QBuffer buffer;
QImageWriter writer(&buffer, "PNG");
writer.write( randomImage() );
[COLOR="red"]QByteArray data;[/COLOR]
QDataStream stream( &data, QIODevice::WriteOnly );
stream << (quint32)buffer.data().size();
data.append( buffer.data() );
socket.write( data );

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this code is to send a picture.
for same purpose:

QBuffer buffer;
  QImageWriter writer(&buffer, "PNG");
  writer.write( randomImage() );
  QByteArray data;
  QDataStream stream(&socket);
  stream << (quint32)buffer.data().size();
  stream << buffer.data();

QBuffer buffer;
  QImageWriter writer(&buffer, "PNG");
  writer.write( randomImage() );
  QByteArray data;
  QDataStream stream(&socket);
  stream << (quint32)buffer.data().size();
  stream << buffer.data();

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works good as well.

1 i am so confused, what is purpose of having QByteArray in first code???

2 and in second code i don't even need socket.write( ) to send data... why>?

3 in first code, dose "stream << (quint32)buffer.data().size();" means write the size into (QByteArray) data?