Can't create an object : initialisation problem ?

[Nyphel]

Small UP, I don't find the solution...
So perhaps someone may find it

[jpn]

A good practice is to allocate objects derived from QObject on the heap (with operator "new"). QObjects allocated on the stack in together with a parent-child relationship tend to cause problems (*). I suggest diving into docs; QObject, Object Trees and Object Ownership..

I'm not sure if this is the problem of yours because I can't see any parent being passed for any object in the example piece of code.. But QObject parent-child relationship sure is a concept a developer must understand while developing with Qt.

(*) A QObject deletes all it's children. A child gets destructed twice in case it was allocated on the stack, 1) by the parent 2) when going out of scope => crash.

[Nyphel]

Hello,

Someone esle gave me the solution on another forum.
My error was to use the QTcpSocket in the constructor of MailChecker while it wasn't initialised :

MailChecker::MailChecker() : QObject()
{	
	connect(socket_r, SIGNAL(error(QAbstractSocket::SocketError)), this, SLOT(afficher_erreur_socket(QAbstractSocket::SocketError)));
}

MailChecker::MailChecker() : QObject()
{	
	connect(socket_r, SIGNAL(error(QAbstractSocket::SocketError)), this, SLOT(afficher_erreur_socket(QAbstractSocket::SocketError)));
}

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The good code is :

MailChecker::MailChecker() : QObject()
{	
	socket_r = new QTcpSocket();
 
	connect(socket_r, SIGNAL(error(QAbstractSocket::SocketError)), this, SLOT(afficher_erreur_socket(QAbstractSocket::SocketError)));
}

MailChecker::MailChecker() : QObject()
{	
	socket_r = new QTcpSocket();
	
	connect(socket_r, SIGNAL(error(QAbstractSocket::SocketError)), this, SLOT(afficher_erreur_socket(QAbstractSocket::SocketError)));
}

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Is was initialising my Socket directly in a function that :
- initialise the socket
- connect to host
- submit a request
- listen the answer
- close the socket
- destroy the socket

Thanks Dudule from developpez.net C++ forums



PS : Thanks jpn, your answer is usefull for me, because I didn't know that