receive data from client via QTcpServer

[Fallen_]

You can only read from the socket if there's something to read.
You try to read a nanosecond after you've send the welcom message. In that time, the client didn't have time to respond.

Suggestions:

void Server::sendWelcomeMessage()
{
	typedef QVector<QTcpSocket*> Connections; // <-- Define this at the class level
	Connections connections; // This too
 
                while (server->hasPendingConnections ()) {
                	QTcpSocket *client = server->nextPendingConnection();
	                connect(client, SIGNAL(disconnected()), client, SLOT(deleteLater()));
                                connect(client, SIGNAL(readyRead()), signalmapper, SLOT(map())); // Signal mapper is defined in the class definition and created in the constructor, see QSignalMapper.
                	signalmapper->setMapping(client, client);
	                client->write("Welcome!");
                }
                connect(signalmapper, SIGNAL(mapped(QObject *)), this, SLOT(clientReadyRead(QObject *)));
}
 
void Server::clientReadyRead(QObject *socket)
{
    QTcpSocket *clientSocket = qobject_cast<QTcpSocket *>(socket);
 
    clientSocket->read...()
}

void Server::sendWelcomeMessage()
{
	typedef QVector<QTcpSocket*> Connections; // <-- Define this at the class level
	Connections connections; // This too

                while (server->hasPendingConnections ()) {
                	QTcpSocket *client = server->nextPendingConnection();
	                connect(client, SIGNAL(disconnected()), client, SLOT(deleteLater()));
                                connect(client, SIGNAL(readyRead()), signalmapper, SLOT(map())); // Signal mapper is defined in the class definition and created in the constructor, see QSignalMapper.
                	signalmapper->setMapping(client, client);
	                client->write("Welcome!");
                }
                connect(signalmapper, SIGNAL(mapped(QObject *)), this, SLOT(clientReadyRead(QObject *)));
}

void Server::clientReadyRead(QObject *socket)
{
    QTcpSocket *clientSocket = qobject_cast<QTcpSocket *>(socket);

    clientSocket->read...()
}

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i get this error:
signalmapper was not declared in this scope

[Fallen_]

nvm, i fixed it myself thx