QDataStream and readBytes

Hi,

In the wake of this thread thread I'm trying to read binary data from a socket, hence the code:

Code:

---

unsigned int totalBytes = 0;
	totalBytes = tcpSocket.bytesAvailable();
	if (totalBytes < 4) return;		// bogus tx...
 
	uint headerSize=sizeof(uint);
	char * header = new char [headerSize];
 
	uint headerBytes=0;
	QDataStream inData(&tcpSocket);
 
	inData.readBytes(header, headerSize);
	headerBytes=atoi(header);

---

Unless I really don't know what I'm doing... ;) (most probably) why does inData.readBytes(header, headerSize); always cause a segfault?

Any pointers welcome.
Thanks in advance,
Pedro Doria Meunier.

Use QDataStream::readRawData(). readBytes() is a complement of writeBytes() and it assumes that the data is in certain format (it also allocates the buffer itself).

Won't it be simplier to write:

Code:

---

uint headerBytes=0;
QDataStream inData(&tcpSocket);
inData >> headerBytes;

---

?

Txs Jacek,

I already tried that only to discover that these devices are stupid enough to send the header and data all at once, so in >> is not an option. I have to read the 1st bytes of what comes to determine the length of the following data... :(

Kind regards,
Pedro Doria Meunier.

Quote:

---

Originally Posted by pdoria

I already tried that only to discover that these devices are stupid enough to send the header and data all at once, so in >> is not an option.

---

Why?

Code:

---

quint16 header;
inData >> header;

---

will read exactly two bytes from the stream into header, leaving the rest intact. Then you can check the header and read more data.

Jacek,

You're absolutely right. This is working now. I don't remember what I did last time... :o
Man... what a ride!!! :D
I sincerely want to thank you for your valuable support... thank you!

Kind regards,
Pedro Doria Meunier.

Ok. last step:

this doesn't work...

Code:

---

quint16 dataLength=0;
 
QDataStream inData(&tcpSocket);
 
while (zerocount < 4 && dataLength==0)
{
	inData >> dataLength;
	if (dataLength==0) zerocount++;
}
 
// exceed number of tries... bogus txs. return.
if (zerocount==3) return;
 
char * data = new char[dataLength];
inData >> data;

---

the data is always 0x0 ... :confused:
So ... please tell me... after in >> dataLength the pointer in the stream is advanced or not?
the operator>> ( char *& s ) is able to convert the binary data into char?

Thanks in advance.

bump.

Must one do this?

Code:

---

char * data = new char[dataLength];
	qint8 c;
	int n;
	for (n=0; n<dataLength; n++) {
		inData >> c;
		data[n]=c;
	}

---

It feels a bit archaic...

Quote:

---

Originally Posted by pdoria

Must one do this?

---

No, you can use readRawData() instead.

Be aware that QDataStream is not a general purpose binary stream but a serialization method. Don't use it if you don't need it.