How do I initialize a static std::map?

Question

I've made a message-only window class, and I'm trying to map HWNDs back to the objects with those handles. I'm trying to do that using a private static std::map<HWND, CMyClass*> belonging to the class, like this:

MyClass.h:

class CMyClass
{
    ...

private:
    HWND        m_hWnd;
    HINSTANCE   m_hInstance;
    LPCSTR      m_szClassName;

    static std::map<HWND, CMyClass*> s_mapHandles;

    ...
};

MyClass.cpp:

std::map<HWND, CMyClass*> CMyClass::s_mapHandles;

but when I try to add to the map, the program crashes. I've tried three different forms, and they all give the same error:

...
m_hWnd = ::CreateWindowEx(0, m_szClassName, "Message Window", 0, 0, 0, 0, 0, HWND_MESSAGE, 0, m_hInstance, 0);
s_mapHandles.insert(pair<HWND, CMyClass*>(m_hWnd, this));

or

...
s_mapHandles.insert(s_mapHandles.end(), pair<HWND, CMyClass*>(m_hWnd, this));

or even

...
s_mapHandles[m_hWnd] = this;

In each case, there crash occurs at a call to _Root() which tries to return _Parent(_Myhead) ; _Parent(_Myhead) returns (_Nodepref)(*_Myhead)._Parent which fails because _Myhead is null.

How do I initialise the map, such that its head is non-null and I can insert things without it crashing? Apologies if I've explained this badly - I'm new to C++.

Answer 1

Are you using it from the constructor of another statically initialized object?

Read C++ FAQ Lite - 10.12 What's the "static initialization order fiasco"?

Answer 2

您根本不需要初始化它，默认情况下应该初始化它。

Answer 3

Just out of curiosity. Is the window handle not null? Because if the window handle comes back as null then the insert will fail.

Answer 4

The original problem may be already solved, but I happen to run in to similar problem (without the static part). I used to have the map inside of a function, then moved it to a class variable. I also got crashes when inserting to the map. It turns out that I needed to delete the all the compiled objects and restart compiling from scratch. Then everything works as expected.

Answer 5

My C++ is a little rusty, but I don't think there's any reason for having that line in your .cpp file. In fact, since it's not a static member, I'm not sure what kind of behavior that would lead to. But like I said, I'm rusty - I could be missing something.

Answer 6

This has probably been solved in the meantime, but just for reference: Here is another solution for the actual problem behind the question: You can store custom data in the GWL_USERDATA field of any Window (I believe using the ::SetWindowLong API function if I remember correctly). If you put your CMyClass pointer in there instead of associating it with the HWND via a map, well, you don't need the map at all, and it is more efficient since all you need to do is typecast the pointer instead of an expensive map lookup.