Re: template question.

From:

"Bo Persson" <bop@gmb.dk>

Newsgroups:

comp.lang.c++

Date:

Wed, 18 Jul 2007 12:17:50 +0200

Message-ID:

<5g67m1F3f6f8uU1@mid.individual.net>

tather wrote:
:: I found these code in http://www.parkscomputing.com
:: but I can not compile it successful.
::
:: ------------------------------------------------
::
:: typedef LONG (__stdcall * forwardFn_t)(HWND, UINT, WPARAM, LPARAM);
:: template<UINT msg> class Handler;
:: template<> class Handler<WM_PAINT>
:: {
:: protected:
:: virtual void OnPaint() = 0;
:: public:
:: LRESULT Handle(WPARAM wParam, LPARAM lParam)
:: {
:: OnPaint();
:: return 0L;
:: }
:: static void Forward(HWND hWnd, forwardFn_t pfn)
:: {
:: (*pfn)(hWnd, msg, 0L, 0L);
:: }
:: };
:: ----------------------------------------------------
:: error C2065: 'msg' : undeclared identifier
::
:: Why the error occur, and How can I resolve it to get the same
:: fuction?

The name msg is the template parameter of the Handler class. In the
specialization of this class, you just have template<>, and the msg
name isn't visible. In this case, its value is WM_PAINT, as this is
what it is specialized for.

That it once used to compile is really a bug that has been fixed in
later editions if the compiler!

Bo Persson