How to Subclass Unicode Window from ANSI Application

Introduction

I am thankfull to Jim Barry and Brian Ross. Both helped me in writing this article. Actually the solution provide by me is the Solution provided by Jim Barry.

Jeffrey Richter in his book Windows 95 A Developer's Guide says:

We achieve subclassing by replacing the address of that window's WndProc. For that we must be a part of the process that created the window. There are numerous method to get in to any process address space, like the WriteProcessMemory() API, \HKLM\Software\Microsoft\Windows\AppInit_Dll (for NT only) or Hooks.

At this time most of the API functions have ANSI and UNICODE versions. For example 

#ifdef UNICODE
#define GetWindowTextLength  GetWindowTextLengthW
#else
#define GetWindowTextLength  GetWindowTextLengthA
#endif

So if our application is ANSI GetWindowTextLenghtA will be used otherwise GetwindowTextLengthW will serve us.

Once we get into address space of our desire process. We use SetWindowLong to replace the original WndProc, that will return us original WndProc address in response. Latter we can use that address to pass messages to original WndProc with the help of CallWindowProc().

Kyle Marsh in his article Safe subclassing in Win32 says:

So CallWindowProc() is supposed to help us with ANSI/UNICODE. But it never does.

From here begins my story.

For some reason I came to the decision that I should subclass the Windows Explorer window. I did that with the help of SetWindowLong() and CallWindowProc(). I use same code over Win9x and NT/2k. On NT/2K I faced a strange problem of having the wrong window title. After subclassing that subclassed explorer window display its title is single letter i.e. "Exploring System (C:)" is "E". I checked the WM_SETTEXT message it receives correct text in lParam.

I start searching for help as I could not figure it out by myself. I posted questions to Microsoft news groups. A guy name Jim Barry helped me by saying:

So I change my code to

if(IsWindowUnicode(hwndToExplorer))
{
	pfnWndProc = (WNDPROC)SetWindowLongW(hwndToExplorer, GWL_WNDPROC, 
				(LPARAM)(WNDPROC)Explorer_SubClassWndProc);
}
else
{
	pfnWndProc = (WNDPROC)SetWindowLongA(hwndToExplorer, GWL_WNDPROC, 
				(LPARAM)(WNDPROC)Explorer_SubClassWndProc);
}

and

if(IsWindowUnicode(hwnd))
{
	lResult = CallWindowProcW((WNDPROC) (DWORD)pfnWndProc, hwnd, 
						uMsg, wParam, lParam);
}
else
{
	lResult = CallWindowProcA((WNDPROC) (DWORD)pfnWndProc, hwnd, 
						uMsg, wParam, lParam);
}

Hence I got the what I want to.

Errors and Omissions are expected/accepted :)