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C Discussion Thread
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Sep 22nd, 2006

what is the use of "&" here

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look at "dc.SelectObject(&pen)" and "dc.SelectObject (&brush)",here no matter I use "&" or not it results the same. why is that?

C Syntax (Toggle Plain Text)
void CMainWindow::OnPaint ()
{
    CPaintDC dc (this);
    CBrush brush (RGB (255, 0, 0));
    CPen pen (PS_NULL, 0, (RGB (0, 0, 0)));
 
    dc.SelectObject(&pen);
    dc.SelectObject (&brush);
    dc.Ellipse (0, 0, 200, 100);
}
void CMainWindow::OnPaint ()
{
    CPaintDC dc (this);
    CBrush brush (RGB (255, 0, 0));
    CPen pen (PS_NULL, 0, (RGB (0, 0, 0)));
    
    dc.SelectObject(&pen);
    dc.SelectObject (&brush);
    dc.Ellipse (0, 0, 200, 100);
}

Last edited by Salem; Sep 22nd, 2006 at 5:56 pm. Reason: tagging

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Sep 22nd, 2006

Re: what is the use of "&" here

> here no matter I use "&" or not it results the same.
Well one or the other is going to produce at least a compiler warning. Choose the one which compiles cleanly.

> why is that?
Sometimes, despite the programmers' best efforts to make a mess of it, it still manages to produce the expected result.
Never confuse "expected results" and "bug free" as meaning the same thing.

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Sep 22nd, 2006

Re: what is the use of "&" here

acctually no warning at all.

But which one is the optimal one here? as you recommend

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Sep 22nd, 2006

Re: what is the use of "&" here

It works because CBrush and CPen are derived from class CGdiObject, which has an operator void* that is being called when you leave out the & symbol. So the & symbol in this case is optional.

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