Does GetDC()->operator HDC() need a ReleaseDC?

[stakon]

Hi all,

I am calling a DLL function OnMouseMove which requires me to pass an HDC.

I am using:

OnMouseMove{
HDC hdc;
hdc = GetDC()->operator HDC();

DllFunc(hdc);
...
}

I don't see any memory leaks but the documentation suggest that when using GetDC(), a ReleaseDC() must follow.

Is this accurate?
Should i rewrite my function as below?

OnMouseMove{
HDC hdc;
CDC *pdc;

pdc = GetDC();
hdc = pdc->operator HDC();

DllFunc(hdc);

ReleaseDC(pdc);
...
}

Thanx in advance!

[Alex F]

GetDC without ReleaseDC may create resource leak, and not memory leak. The second code version is correct.

[OReubens]

ReleaseDC is only necessary for common DC's.
If the window owns a DC (private or class dc) ReleaseDC is not necessary (although recommended).

So yes, the 2nd version is prefered, although you can write it more compact.

CDC *pdc = GetDC();
DllFunc(pdc->GetSafeHdc());
ReleaseDC(pdc);

[VictorN]

And to avoid the problems with ReleaseDC - just don't use GetDC at all!
There is the CClientDC class (MFC) which implicitly calls GetDC in its ctor and ReleaseDC in the dtor. So

CClientDC dc;
hdc = dc.operator HDC();

DllFunc(hdc);
...

[stakon]

Thanx guys!

You have all been very helpful.

[Marc G]

I also would suggest to call GetSafeHdc() (like in OReubens post) instead of operator HDC().