[Solved]QVector extract subvector

[TOAOMatis]

Hi all,

currently I'm developing an UdpSocketListener, which snoops udp broadcasts from the network.
The data is received and the datagram is extracted. Within this datagram the following data is packed:
4 bytes Message Transaction ID, this is cast to an ulong
1 byte Protocol Version, used for distinguishing different versions
1 byte data length, this indicates the data size embedded within this datagram. Between 0 and 134 bytes.
0..134 bytes data

Like I said, the datagram is received and put in a QVector<uchar>, then the MTID is read and the datasize is read. If there is data available, which is normally the case, this needs to be assigned to an QVector<uchar>.
@QVector<uchar> AcpPacket::toPacket(QVector<uchar> datagram)
{
ulong tid = 0;
uchar size = 0;
uchar pver = 0;
QVector<uchar> data;
/* There must be an easier way to extract an ulong from 4 bytes of data /
tid = datagram.takeFirst() << 24;
tid += datagram.takeFirst() << 16;
tid += datagram.takeFirst() << 8;
tid += datagram.takeFirst() << 0;
pVer = datagram.takeFirst();
size = datagram.takeFirst();
/ While there is no header data left any more from the packet, the remaining bytes must be data */
data = datagram();
return data;
}@
What I would like to achieve is the following (pseudo code)
@tid = datagram.at(0).toLong();
pVer = datagram.at(4);
size = datagram.at(5);
data = datagram[6]...datagram[6+size];
@

Is this possible? I come from POSIX C, where you can achieve this with pointer arithmetic, but I'm struggling with the Qt language.

Many thanks in advance!

TOAOMatis

[Asperamanca]

Maybe something like
@data = datagram.mid(6);@

[TOAOMatis]

You sir (ma'am), are a genius!
Many thanks. I don know why I've missed this in the help files.

The only problem remains; how can I cast the 4 bytes to a long.

[Asperamanca]

You are welcome.
Please mark the thread solved by putting [Solved] in front of the title (to do that, edit your original post).

[TOAOMatis]

[quote author="Asperamanca" date="1386836587"]You are welcome.
Please mark the thread solved by putting [Solved] in front of the title (to do that, edit your original post).[/quote]

Yes, I will do. But I have another question pending (I've edited my previous post), how to cast 4 bytes from the QVector to an ulong.

[Asperamanca]

QVector doesn't offer any specific support for that (as far as I know). However, this can be done using regular C/C++
I found a discussion about that "here":http://stackoverflow.com/questions/14591763/c-2-char-array-elements-into-short-int

[TOAOMatis]

Ok, thanks for your quick reply.

I already do it that way;
@tid = datagram.takeFirst() << 24;
tid += datagram.takeFirst() << 16;
tid += datagram.takeFirst() << 8;
tid += datagram.takeFirst() << 0;@

Will mark this thread as resolved :-)