How do I use QTcpSocket properly ?

[mnemonic_fx]

Nop... If that's really the code you're using (not talking about completeness here just exactitude...) Then the connection must close as soon as the execution leaves the scope where your socket is instantiated (loop, function, whatever) because you don't use dynamic allocation but heap allocation... Thus the socket object is destroyed and stops communicating with your server... I think you should read some more about OOP and C++...

When I call the function like this : (session is a pointer to class object)

session->tcpSocket.write((const char*)buf,len);
session->tcpSocket.waitForBytesWritten();

session->tcpSocket.write((const char*)buf,len);
session->tcpSocket.waitForBytesWritten();

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I get this error :

Unhandled exception at 0x670afb8a (QtCored4.dll) in MyProgram.exe: 0xC0000005: Access violation reading location 0xcdcdcdd9.

and it's break at this location :

private:
-> Q_DECLARE_PRIVATE(QIODevice)
     Q_DISABLE_COPY(QIODevice)

private:
-> Q_DECLARE_PRIVATE(QIODevice)
     Q_DISABLE_COPY(QIODevice)

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I access the tcpSocket object that was created in a running thread.
If I want to maintain the connection what should I do ?
create a static object ?


By the way isn't heap allocation & dynamic allocation is the same thing, just with different terms ?

I read this on a book, chapter 20.3 of "An Introduction to Design Patterns in C++ with Qt" :

The heap or free storage (dynamic storage): Objects created via new are examples.
The lifetime of a heap object is determined entirely by the use of new and delete.
In general, the allocation and freeing of heap objects should be in carefully encapsulated classes.

And I read this on a book, chapter 3 of "Memory Management, Algorithms and Implementations in C-C++" :

Heap memory allocation, also known as dynamic memory allocation
(DMA), consists of requesting memory while an application is running
from a repository known as the heap.

[fullmetalcoder]

1. Generally speaking accessing class members directly is wrong. Instead you should provide wrapper functions/slots/whatever to handle that
2. Sounds like your QTcpSocket object is an object and not a pointer. This is also considered as bad design because it is NOT a type which can be copied (noticed the Q_DISABLE_COPY() macro ?) just like basic types (int, QString, QPixmap QList<>, ... for instance) which implies that in most cases, and especially when using such objects outside of their creation scope, they should be created through new and accessed via pointers...
3. There seems to be quite a misunderstanding about semantics... I used to to think that "heap allocation" referred to objects created as objects (i.e. without "new" operator) which were automatically deleted when the program leaved the creation scope whereas "dynamic allocation" referred to process of creating objects via "new" and deleting them manually with "delete". I might have been misleaded as far as names are concerned (and I shall investigate this) but my remarks still stand in your case : use pointers when dealing with network objects!

Hope this helps.

[mnemonic_fx]

Ok, I think I understand about dynamic allocation and using pointers, I try to use that, but still.. it doesn't solve my problem.

I declare CMsgSession *session on CMsgClient private member.
I write this on the constructor :

CMsgClient::CMsgClient()
{
	session = new CMsgSession();
}

CMsgClient::CMsgClient()
{
	session = new CMsgSession();
}

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And I declare QTcpSocket *tcpSocket on CMsgSession public member, I write this on the constructor :

CMsgSession::CMsgSession(QObject *parent) : QThread(parent), workerQuitFlag(false)
{
    tcpSocket = new QTcpSocket();
}

CMsgSession::CMsgSession(QObject *parent) : QThread(parent), workerQuitFlag(false)
{
    tcpSocket = new QTcpSocket();
}

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and I access the tcpSocket like this :

session->tcpSocket->write(buf, len);

it causes access violation, it's getting more confusing,
but thanks anyway..

[jacek]

session->tcpSocket.write((const char*)buf,len);

How do you initialize buf and len?

and it's break at this location : (...)

Could we see the backtrace?