GetClipboardData() in C++

[Theta]

Hi, I am relatively new to Windows programming and I am reading through a book. The book has samples that don't always work with C++, but C. I was trying to convert one of the samples from C to C++, and I am just curious if I am doing it right, IE: I've allocated memory correctly, and then deallocated it, and did not make any dumb errors with casting.

I figured I ask since I want to ensure I am handling memory correctly. Here is my code (Just the important part).

LRESULT CALLBACK WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
	 static wchar_t			*wText;
	 wchar_t				*wGlobal;
	 HGLOBAL				hGlobal;
	 HDC					hdc;
	 PAINTSTRUCT			ps;
	 RECT					rc;

	switch(msg)
	{
		case WM_CREATE:
			
			OpenClipboard(hWnd);
			
			if(hGlobal = GetClipboardData(CF_UNICODETEXT))
			{
				
				wGlobal = (wchar_t*)GlobalLock(hGlobal);

				// Allocate memory from the clipboard
                wText = new wchar_t[GlobalSize(hGlobal)];

				// Make a copy of the text in the clipboard
                lstrcpy (wText, wGlobal);

				GlobalUnlock (hGlobal);
				InvalidateRect (hWnd, NULL, TRUE) ;
			}

			CloseClipboard();
			
			break;

		case WM_CLOSE:

			DestroyWindow(hWnd);

		break;

		case WM_PAINT:
			
			// Draw the text in the clipboard

			hdc = BeginPaint(hWnd,&ps);

			GetClientRect(hWnd,&rc);

			if(wText != NULL) // But only if there is something in the clipboard.
			{
				DrawText(hdc,wText, -1,&rc,DT_LEFT | DT_WORDBREAK);
			}

			EndPaint(hWnd,&ps);

		break;
		
		case WM_DESTROY:

			if(wText) // Deallocate memory if any was allocated.
			{
				delete[] wText;
			}

			PostQuitMessage(0);

		break;

		default:

			return DefWindowProc(hWnd, msg, wParam, lParam); 

		break;
	}
	return 0;
}

[Moooce]

Looks OK to me but i'll chime in with a question. Would it be worth checking wText is Null before allocating space?
static wchar_t *wText=NULL;

if(wText!=NULL)
  delete [] wText;
wText = new wchar_t[GlobalSize(hGlobal)];

It's probably not relevant for your program, but what if a user was to close a window (case WM_CLOSE:) does that call WM_DESTROY to deallocate the memory? If not then opening a new window would reallocate the memory twice and you'd have a memory leak.

I'm not sure which is why I ask.

[Theta]

You are right, I should be checking if it is null before allocating it. Thanks for pointing that out!

If I understand the second part of your post correctly, you are asking if WM_CLOSE calls WM_DESTROY so that WM_DESTROY can deallocate memory? If so, yes, that is what it does. When WM_CLOSE occurs, it calls DestroyWindow, which places a WM_DESTROY message into the message queue. When WndProc receives this, the program deallocates the memory associated with wText if it has been allocated.

[Computergeek01]

As far as that checking for NULL stuff with wText, I would use the "ZeroMemory(...)" macro from Win32. This way you KNOW that it's blank when you go to use it. I guess this is a style preference but it's worth mentioning in my mind.

Double check that logic on Line 16, you're assigning the handle from "GetClipboardData(...)" to 'hGlobal' not comparing anything.

[Theta]

For Line 16, yeah I know about that, that was how it was in the book I was using.

As for ZeroMemory. I looked it up, but could not really find a good example of how to use it anywhere, but I am going to take a guess you mean to do this:

                wText = new wchar_t[GlobalSize(hGlobal)];
				ZeroMemory(wText,GlobalSize(hGlobal));

[modoran]

ZeroMemory() is just a macro, look at memset() function to understand what it does.

[Theta]

Ah, okay now I get it. Thanks, modoran!