Qt/C++ QTcpSocket causes memory leak, not sure why

Question

I am creating a simple(ish) telnet server and am now debugging with valgrind. the code runs great, but valgrind complains about memory lost when the program terminates...and the culprit is the line where I create a new QTcpSocket:

void TelnetConnection::run()
{
    tcpSocketPtr = new QTcpSocket();  // ** remove this due to parent error
    if (!tcpSocketPtr->setSocketDescriptor(socketDescriptor)) {
        emit error(tcpSocketPtr->error());
        return;
    }
}

I tried passing 'this' to the QTcpSocket() but then the signal-slots I try to connect complain about being associated with a different parent. Is this the problem? A clue? And...what would the answer be?

I delete/free the tcpsocketptr by assigning it a value of 0 as per below. Is that right?

void TelnetConnection::clientDisconnected()
{
    tcpSocketPtr = 0; // ** Cure memory loss?
    TelnetConnection::s_clientCount--;
    Logger *log =  Logger::instance();
    log->record(Logger::Information,EVENTID_TELNET_DISCONNECTION,"Telnet client "+QString::number(m_clientNumber) +": Disconnecting");
    QThread::quit();  // Exit ths event loop for this thread
}

I showed the code called when the client has disconnected...and where I hopefully free the memory allocated for the socket. Is this correct? — TSG, Oct 09 '13 at 06:25
You don't `delete` the memory zone pointed by `tcpSocketPtr` you simply clear the pointer (without doing anything to the memory zone and the `QTcpSocket` object!). — Basile Starynkevitch, Oct 09 '13 at 06:27

It'sPete · Accepted Answer · 2013-10-09T07:25:56.597

7

For every time you call "new" you MUST call "delete." As the comments have suggested, you point the pointer to 0, but never call delete.

Edited to add a YT video of a good explanation of the concepts: http://www.youtube.com/watch?v=_749lj2yb8Y Essentially you are never freeing the memory you request from the CPU, hence you memory leak. A simple call to delete will solve this.

edited Oct 09 '13 at 07:25

answered Oct 09 '13 at 07:19

It'sPete

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Wow - big wrong assumption on my part...I thought c++ had a heap manager that cleaned up after me. I'll have to use delete. Thanks. – TSG Oct 09 '13 at 14:45

Qt/C++ QTcpSocket causes memory leak, not sure why

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