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Freeing resource for custom caret's bitmap

Posted on 1998-09-15
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278 Views
Last Modified: 2013-11-20
I'm using the code below to display a slanted caret in a custom edit window.   Although it displays fine, if I watch my resource meter, it appears as though system/gdi resources are not being freed properly.   I believe the resource for the bitmap within the caret is not released properly.  Any suggestions?

      if ( lf.lfItalic ) {
        int hh = lf.lfHeight ;
        HDC hDCwin = ::GetDC( hWnd ) ;
        HDC hDC = CreateCompatibleDC( hDCwin ) ;
        int ww = lf.lfWidth ;

        caretBitmap = ::CreateCompatibleBitmap( hDC, ww+1, hh ) ;
        prevBitmap = (HBITMAP) ::SelectObject( hDC, caretBitmap ) ;

        ::PatBlt( hDC, 0, 0, ww+1, hh, WHITENESS);
        ::MoveToEx( hDC, 0, hh, NULL ) ;
        ::LineTo( hDC, ww, 0 ) ;
        ::MoveToEx( hDC, 1, hh, NULL );
        ::LineTo( hDC, ww+1, 0 );
        ::PatBlt( hDC, 0, 0, ww+1, hh, PATINVERT );
        ::CreateCaret( hWnd, caretBitmap,caretWidth,caretHeight );

        ::DeleteObject( (HGDIOBJ) ::SelectObject( hDC, prevBitmap ) );
        ::DeleteDC( hDC ) ;
        ::ReleaseDC( hWnd, hDCwin ) ;
      }
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Question by:JohnWeidner
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3 Comments
 
LVL 2

Accepted Solution

by:
jstolan earned 50 total points
ID: 1322165
Each call to CreateCaret must be matched to a call to DestroyCaret.  If you're done with it at the point in the code you're showing, then you can destroy it there.  If you need it to persist after this function terminates, then you need to move the CreateCaret function (perhaps to the point where the window is created), and place a matching DestroyCaret function at the point where the window is destroyed.
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LVL 2

Expert Comment

by:jstolan
ID: 1322166
By the way, you'll still have to free the bitmap memory separately since DestoryCaret does not free this memory.
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Author Comment

by:JohnWeidner
ID: 1322167
Yes, I was calling DestroyCaret() in another section of code.   But I was relying on the line    

     ::DeleteObject( (HGDIOBJ) ::SelectObject( hDC, prevBitmap ) );  

which I called right after creating the bitmap (see code from question) to free up the bitmap's memory.    However, eventhough the DeleteObject call was returning success, it must not have been working properly there.   I moved the DeleteObject call to the same section of code as the DestroyCaret and now the memory leak is gone.  

Thanks!
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