Public member not initialized - c++

Question

I am making a client server application, with the server having a GUI. I am using Qt.
For communication I am using pipes.
I have divided the server application into a backend, and a GUI. The backend has a PipeServer class, and in the GUI, I have overriden functions like onReceiveMessage etc.
Everything worked fine until I decided to add a std::queue as a base class member.
At the start of the application, I get an exception, and upon inspection it seems that my queue does not start with 0 elements. In fact it seems like the queue is not initialized at all. There are 2 possibilites: it could be because I the GUI class inherits 2 classes, and somehow the second base class, which is my PipeServer does not properly initialize its members, or it could be because the pipeServerGUI object is moved to a different thread by QT.
Any ideas on how I could solve this?
Relevant code:
class HookServer
{
PIPEINST Pipe[INSTANCES];
HANDLE hEvents[INSTANCES];
VOID DisconnectAndReconnect(DWORD);
BOOL ConnectToNewClient(HANDLE, LPOVERLAPPED);
VOID GetAnswerToRequest(LPPIPEINST);
public:
std::queue<std::string> messages;
int init(std::string pipename);
int run();
virtual void onNewConnection() {};
virtual void onReceiveMessage(std::string message) {};
};
class HookServerGUI : public QObject, public HookServer
{
Q_OBJECT
void onReceiveMessage(std::string message);
void onNewConnection();
public slots:
void doWork() {
init("\\\\.\\pipe\\hookpipe");
run();
}
signals:
void signalGUI(QString message);
};
//GUIServerCreation
QThread *thread = new QThread;
HookServerGUI* worker = new HookServerGUI;
QObject::connect(worker,SIGNAL(signalGUI(const QString&)),this,SLOT(processMessage(const QString&)));
worker->moveToThread(thread);
thread->start();
QMetaObject::invokeMethod(worker, "doWork", Qt::QueuedConnection);
EDIT:
The exception is a access violation exception. It happens in this part of code:
VOID HookServer::GetAnswerToRequest(LPPIPEINST pipe)
{
onReceiveMessage(pipe->chRequest);
if(!messages.empty())
{
std::string s = messages.front();
messages.pop();
strcpy(pipe->chReply,s.c_str());
pipe->cbToWrite = strlen(s.c_str()+1);
}
}
Since messages.empty() return some huge number, it tries to read the first object and somehow fails.
There is also no PipeServerGUI constructor.
EDIT2:
I solved part of this problem by placing parenthesis after new HookServerGUI();
The problem is that still the function does not work, and throws a access violation exception. It happens on the front() line. When checked in a debugger, the function does have 1 element, so it is not because it is empty. Any ideas?
EDIT3:
With the second run, unfortunately the queue.size() is still incorrect. Seems like a data race to me.

Answer 1

The problems are in the code that you don't show, and it's a classic case of a memory bug, it looks like. Some code somewhere is writing on memory it doesn't own. Probably you have a bug in the way you use winapi. You need to create a minimal, self-contained test case.
I think you might be shooting yourself in the foot by not using QLocalSocket: on Windows, it's a named pipe - exactly what you want.
Besides, this is C++ code. There is no reason at all to put either PIPEINST or HANDLE into a raw C array. Use QVector or std::vector. Probably the rest of the code is full of C-isms like that, and something somewhere goes wrong.
I wouldn't discount a buffer overrun, since obviously you are ignoring the size of the buffer in PIPEINST from the - the strcpy can overrun the buffer. I'm also not sure that PIPEINST from the example code is using the same character type as what std::string::c_str() is returning.
Even if you wanted to implement your code using explicit pipes without QLocalSocket, you should still use C++, QString etc. and understand what's going on with your data.