Cannot read complete data, bytes available != actual bytes read

Kavita123

Hello All,

I am a newbie to QT. I am developing an application that is using QTCPSocket.
I have created a signal for reading as below:
@
connect(m_pSocket,SIGNAL(readyRead()),SLOT(SocketDataReceived()));
@

and code to read data is:
@
void ABC::SocketDataReceived()
{
int nBytesAvaialble=m_pSocket->bytesAvailable();
LOGDEBUG(CM,"SocketDataReceived : bytes Available initialially = " << nBytesAvaialble);

QString m_qstrNextMesssage;

while (nBytesAvaialble > 0)
{
    m_qstrNextMesssage.append(m_pSocket->read(nBytesAvaialble));
    nBytesAvaialble = m_pSocket->bytesAvailable();
}

if(m_qstrNextMesssage.length() <= 0 )
{
    LOGWARN(CM, "No data is read in this read API");
    return;
}
LOGDEBUG(CM, "Bytes read = " << m_qstrNextMesssage.length());
LOGDEBUG(CM, m_qstrNextMesssage.toLatin1().data());
emit DataReceived(m_qstrNextMesssage);
m_qstrNextMesssage.clear();

}
@

But when I run this code, the log I am getting shows that available bytes are not equal to bytes read (I tried using read() and then readAll() APIs).
@
[01/16/2015 14:53:05:801] [15976] [DEBUG] [CM] SocketDataReceived : bytes Available initialially = 412
[01/16/2015 14:53:05:801] [15976] [DEBUG] [CM] Bytes read = 145

Received data of length 145

[01/16/2015 14:53:06:274] [15976] [DEBUG] [CommunicationManager] SocketDataReceived : bytes Available initialially = 146
[01/16/2015 14:53:06:294] [15976] [DEBUG] [CommunicationManager] Bytes read = 145

Received data of length 145
@

So, in 1st read call bytes available = 412, actual bytes read = 145
in 2nd read call bytes available = 146, actual bytes read = 145

So, where are 412-145 = 267 ? they should be available in next read call right ? So in next read should show bytes available as atleast 267.

What is causing the loss of data here ? Please help.

-Thanks,
Kavita

[Edited - Please use code tags "@@" - p3c0]

Jeroentjehome

First of all, when placing code please use the @ before and @ after the snippets. Then the forum will display them as if real code.
The we might be able to support you.

raven-worx

i don't know which data you are receiving on the socket, but count the read bytes directly and not from the string. Try this:
@
qint64 nBytesAvaialble=m_pSocket->bytesAvailable(); //<-- not using qint64 may cause possible loss of int-data here
...
QByteArray readData = m_pSocket->read(nBytesAvaialble); // or use readAll()
qint64 readBytes = readData.size();
m_qstrNextMesssage.append(readData);
@