QObject: no such slot QThread::readyRead() - c++

Question

I am trying to figure out how to correctly use Qt TCP Sockets, as well as multithreading. I want, as a test project in support of something more complex but similar I will try in the future, to do the following: a simple application that either listens for exactly one incoming connection, or connects to a serversocket; next it prints everything it receives over that socket.
The situation where I connect to a serversocket (I use netcat with the -l option for this) works fine: everything netcat sends to my application is printed correctly. However, when I use my program to listen for that one incoming connection (generated by netcat), the connecting succeeds but then I get this runtime error:
QObject::connect: No such signal QThread::readyRead() in ..\QTcpTest\listener.cpp:8
Here is the entire code (don't mind the plain C I/O I use sometimes, I'll remove this later):
[ main.cpp ]
#include "peer.h"
#include <QCoreApplication>
#include <QThread>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static bool askIfServer();
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
Peer *p;
int rval;
if (askIfServer())
p = new Peer;
else
p = new Peer(false);
rval = a.exec();
delete p;
return rval;
}
static bool askIfServer()
{
bool isServer;
char ibuf[BUFSIZ];
fputs("Choose \'host\' or \'join\': ", stderr);
fgets(ibuf, BUFSIZ, stdin);
ibuf[strlen(ibuf) - 1] = '\0';
fflush(stdin);
if (strcmp(ibuf, "host") == 0)
isServer = true;
else if (strcmp(ibuf, "join") == 0)
isServer = false;
else
{
fputs("Failure.\n", stderr);
exit(-1);
}
return isServer;
}
[ peer.h ]
#ifndef PEER_H
#define PEER_H
#include "listener.h"
#include <QObject>
#include <QThread>
#include <QtNetwork/QTcpSocket>
#include <QtNetwork/QTcpServer>
class Peer : public QObject
{
Q_OBJECT
public:
static const quint16 PORT = 5483;
explicit Peer(bool isHost = true, QString hostname = "localhost", QObject *parent = 0);
public slots:
void acceptPeer();
private:
bool _isHost;
QTcpServer *_server;
QTcpSocket *_socket;
QThread *_lThread;
Listener *_listener;
};
#endif // PEER_H
[ peer.cpp ]
#include "peer.h"
Peer::Peer(bool isHost, QString hostname, QObject *parent) :
QObject(parent),
_isHost(isHost)
{
if (_isHost)
{
_server = new QTcpServer;
connect(_server, SIGNAL(newConnection()), this, SLOT(acceptPeer()));
_server->listen(QHostAddress::Any, PORT);
}
else
{
_socket = new QTcpSocket;
connect(_socket, SIGNAL(hostFound()), this, SLOT(acceptPeer()));
_socket->connectToHost(hostname, PORT);
}
}
void Peer::acceptPeer()
{
disconnect(this, SLOT(acceptPeer()));
if (_isHost)
{
_socket = _server->nextPendingConnection();
delete _server;
_server = NULL;
}
_lThread = new QThread;
_listener = new Listener(_socket);
_listener->moveToThread(_lThread);
_lThread->start();
}
[ listener.h ]
#ifndef LISTENER_H
#define LISTENER_H
#include <iostream>
#include <QObject>
#include <QByteArray>
#include <QtNetwork/QTcpSocket>
using std::cout;
class Listener : public QObject
{
Q_OBJECT
public:
explicit Listener(QTcpSocket *socket, QObject *parent = 0);
public slots:
void acceptData();
private:
QTcpSocket *_socket;
};
#endif // LISTENER_H
[ listener.cpp ]
#include "listener.h"
Listener::Listener(QTcpSocket *socket, QObject *parent) :
QObject(parent),
_socket(socket)
{
// I guess this is where it goes wrong
connect(_socket, SIGNAL(readyRead()), this, SLOT(acceptData()), Qt::QueuedConnection);
}
void Listener::acceptData()
{
QByteArray data = _socket->readAll();
cout << data.constData();
}
The thing I do not get is that the error message claims that I try to connect some signal from QThread (and I clearly do not: see listener.cpp:8); even stranger is that this only happens when the socket is created by the QTcpServer instance, not in the other case. What am I missing?
EDIT: SOLVED
See my own answer.

Answer 1

I do not use an extra thread anymore (see comment). The problem was deleting the QTcpServer instance in Peer::acceptPeer(), once a connection was established. I thought that I could delete it because I only need that one socket QTcpServer::nextPendingConnection() returns. Apparently this is wrong, the socket is probably destroyed as well, leaving me with a rogue pointer (I think) crashing the program. Now I only call _server->pauseAccepting(); right after I get the socket, and all works fine.
Here is the change I've made:
void Peer::acceptPeer()
{
disconnect(this, SLOT(acceptPeer()));
if (_isHost)
{
_socket = _server->nextPendingConnection();
_server->pauseAccepting(); // no deletion
}
_listener = new Listener(_socket);
}