sender() returns the pointer to the object which emitted the signal (http://doc.qt.io/qt-5.6/qobject.html#sender). In this case it is a pointer to QLocalSocket, so you need to cast it from QObject* to QLocalSocket* using qobject_cast

@LuGRU Why not to use: QSharedMemory and You don't need to worry about message formatting. Because I run process with different account. First process run from System account and second from local account When I read SharedMemory in another process I have error "QSharedMemory handle doesn't exist"