Question

Using: VS2008, Win32, C/C++

I’m trying to encapsulate my entire dialog window into a class for reusability. Sort of like a custom control. In doing this, I am moving my seperate functions into a class. The following struct design though is giving me problems, with Visual Studio outputting: error C2334 ‘{‘.

It’s a simple message map layout. But I can’t seem to escape this C2334 error. 🙁

Here is my class code snippet.

class CScrollingListDlg { private:  LRESULT DoCommandMain (HWND hWnd, UINT wMsg, WPARAM wParam, LPARAM lParam); LRESULT DoPaintMain   (HWND hWnd, UINT wMsg, WPARAM wParam, LPARAM lParam); LRESULT DoAnimationTimer (HWND hWnd, UINT wMsg, WPARAM wParam, LPARAM lParam); LRESULT DoHandleTouch (HWND hWnd, UINT wMsg, WPARAM wParam, LPARAM lParam); LRESULT DoDestroyMain (HWND hWnd, UINT wMsg, WPARAM wParam, LPARAM lParam);  // // message maps // // Generic defines and data types. struct decodeUINT {     UINT Code;     LRESULT (*Fxn)(HWND, UINT, WPARAM, LPARAM); };  struct decodeCMD {     UINT Code;     LRESULT (*Fxn)(HWND, WORD, HWND, WORD); };  // WM_Message dispatch table for MainWndProc.  // // ***  error C2334 '{'  *** // const struct decodeUINT MainMessages[] = {     WM_PAINT,   DoPaintMain,     WM_DESTROY, DoDestroyMain,     WM_QUIT,    DoDestroyMain,     WM_COMMAND, DoCommandMain, };   }; 

What am I missing here?

Thanks.

Answer 1

You cannot specify initialisers for non-static members that way — you would normally need to declare the array and then populate it inside the constructor… Except that, in fact there is no way to initialise const member arrays in C++ (see this thread).

If you are prepared to share MainMessages amongst all instances of CScrollingListDlg (which I suspect was your intention all along), you should make it static, in which case you can declare:

static const decodeUINT MainMessages[];  // 'struct' keyword unnecessary 

inside the class definition of CScrollingListDlg, and then define it outside the class:

const CScrollingListDlg::decodeUINT CScrollingListDlg::MainMessages[] = {     WM_PAINT,   DoPaintMain,     WM_DESTROY, DoDestroyMain,     WM_QUIT,    DoDestroyMain,     WM_COMMAND, DoCommandMain,    // The comma *is* allowed -- thanks Josh! }; 

In order for this to actually compile, you’ll need to make DoPaintMain(), DoDestroyMain(), etc. static as well — as it stands, they are all per-object methods that implicitly take a this pointer, so they can’t actually be contained in a function pointer of type LRESULT (*Fxn)(HWND, UINT, WPARAM, LPARAM). (You could leave them as non-static methods and change the pointer type in decodeUINT to a pointer-to-member-function type, but that’s probably not what you want.)

[EDIT: Thanks to Josh for some helpful comments!]