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++.

Can you post the code where you call insert? also the lines before it? — Jaime Garcia
– Jaime Garcia, Commented Jul 27, 2009 at 13:35

dalle · Accepted Answer · 2009-07-27 13:49:47Z

6

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"?

answered Jul 27, 2009 at 13:49

dalle

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1 Comment

Simon Over a year ago

I don't believe so, but that's an interesting (and horrible) problem that I'll look out for. Thanks for pointing it out!

OneOfOne · Accepted Answer · 2009-07-27 13:40:13Z

1

You don't need to initialize it at all, it should be initialized by default.

answered Jul 27, 2009 at 13:40

OneOfOne

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Comments

Jaime Garcia · Accepted Answer · 2009-07-27 14:18:07Z

1

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

answered Jul 27, 2009 at 14:18

Jaime Garcia

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2 Comments

anon Over a year ago

Only the second time (because it will be a duplicate) - and that will not cause the problem he's asking about.

Simon Over a year ago

The problem happens whether or not the window handle is null.

polyglot · Accepted Answer · 2010-06-24 13:11:36Z

1

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.

answered Jun 24, 2010 at 13:11

polyglot

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Avdi · Accepted Answer · 2009-07-27 13:35:57Z

0

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.

answered Jul 27, 2009 at 13:35

Avdi

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1 Comment

Simon Over a year ago

Sorry, forgot to put 'static' here. In our code, it is static.

Peter · Accepted Answer · 2011-08-01 19:45:19Z

0

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.

answered Aug 1, 2011 at 19:45

Peter

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