exc_bad_access crash in QT app

I'm writing a QT app and I'm very rusty with C++, so I'm guessing that's the problem. I've got a crash with an exc_bad_access signal on my Mac, whic开发者_StackOverflow社区h means I'm doing something wrong with memory. Here's my code:

void MainWindowController::showMainWindow() {
    MainWindow *w = mainWindow();
    w ->show();
}

MainWindow *MainWindowController::mainWindow() {
    if (NULL != _mainWindow)
        return _mainWindow;

    // otherwise, we need to load it and return it

    _mainWindow = new MainWindow(0);
    return _mainWindow;
}

_mainWindow is an instance variable, a pointer (as you might have guessed from the function signature). It's a simple lazy-loading. I think I'm doing memory management OK, as this class owns the object (which is later deleted in the destructor).

The crash occurs on the w -> show(); line, QT complains its somewhere inside the QWidget show() function, which doesn't really make sense to me.

Can somebody help me out? Thanks!

---

Turns out it was something even simpler. I'm used to Objective-C, where ivars are automatically initialized to 0. C++ doesn't do this. So, I had to make sure _mainWindow was initialized to NULL in the constructor. Problem solved.