Returning CBitmap* pointer

_Flaviu

I have wrote a method that load and rescale a CBitmap:

CBitmap* CMyDlg::LoadPicture(CString strFile)
{
int m_nPictureSize = 170;
CBitmap* pBitmap = NULL;
HBITMAP hBitmap = (HBITMAP)::LoadImage(NULL, strFile, IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);
if(NULL != hBitmap)
{
CBitmap Bitmap, MemBitmap;
Bitmap.Attach((HBITMAP)hBitmap);
// rescale CBItmap ....
// retrieve the final bitmap
CBitmap* pFinalBitmap = MemDC.SelectObject(pOldBitmap);
SourceDC.SelectObject(pOldBmp);
pBitmap = new CBitmap;
pBitmap->Attach((HBITMAP)pFinalBitmap->GetSafeHandle());
BITMAP bm3;
pBitmap->GetBitmap(&bm3);
TRACE("Width and height INSIDE if condition: %d|%d\n", bm3.bmWidth, bm3.bmHeight);
}
BITMAP bm4;
pBitmap->GetBitmap(&bm4);
TRACE("Width and height OUTSIDE if condition: %d|%d\n", bm4.bmWidth, bm4.bmHeight);
return pBitmap;
}

I want to use this method in order to add this created CBitmap pointer to add them into CTypedCBitmapList:

	CBitmap\* pImage = LoadPicture(strPath);
	if(NULL == pImage->GetSafeHandle())
		return 0;
	m\_PtrArrayBitmap.Add(pImage);

Ok, but the strange thing is that pBitmap from inside of LoadPicture method has correct size inside of 'if' condition, and wrong size outside of 'if' condition:

Width and height INSIDE if condition: 170|170
Width and height OUTSIDE if condition: -858993460|-858993460

Why ? It is not the same pBitmap object ? Could you help me ? Kindly thank for any further help !

Lost User

It appears that the bitmap you are pointing to is a temporary object whose scope is only within the if block. In the following block of code where do pOldBitmap and pOldBmp come from?

	CBitmap\* pFinalBitmap = MemDC.SelectObject(pOldBitmap);
	SourceDC.SelectObject(pOldBmp);
	pBitmap = new CBitmap;
	pBitmap->Attach((HBITMAP)pFinalBitmap->GetSafeHandle());

_Flaviu

I think I figure out why it doesn't work ... pOldBitmap and pOldBmp are decalred inside of 'if' statement:

if(NULL != hBitmap)
{
	//// ......
	// select memory bitmap into memory dc
	CBitmap\* pOldBitmap = MemDC.SelectObject(&MemBitmap);
	// create a source dc
	CDC SourceDC;
	SourceDC.CreateCompatibleDC(&cdc);
	// select into source dc the source bitmap
	CBitmap\* pOldBmp = SourceDC.SelectObject(&Bitmap);
	//// ......
	// retrieve the final bitmap
	CBitmap\* pFinalBitmap = MemDC.SelectObject(pOldBitmap);
	SourceDC.SelectObject(pOldBmp);
	pBitmap = new CBitmap;
	pBitmap->Attach((HBITMAP)pFinalBitmap->GetSafeHandle());

BITMAP bm3;
pBitmap->GetBitmap(&bm3);
TRACE("Width and height INSIDE if condition: %d|%d\n", bm3.bmWidth, bm3.bmHeight);
}
BITMAP bm4;
pBitmap->GetBitmap(&bm4);
TRACE("Width and height OUTSIDE if condition: %d|%d\n", bm4.bmWidth, bm4.bmHeight);
return pBitmap;

Lost User

Well, that is quite different from the code in your original question.