What does it mean to GetDC(0&)?

Question

I am reading some VB6 to convert to C#. What does this line mean? Is 0& equivalent to IntPtr.Zero?

//'Get a Device context
hdc = GetDC(0&)

This value is used to pinvoke, so I'm not sure IntPtr.Zero makes sense since we need to be selecting some object.

OldFont = SelectObject(hdc, ObjFont)

Note, ObjFont is populated via

//'Get the Window's font
ObjFont = SendMessage(hwnd, WM_GETFONT, 0, 0&)//there's that mysterious 0& agaain.

score 6 · Accepted Answer · edited May 23 '17 at 10:24

6

It is a (VB6) type declaration character. Have a look at this question for more details on these.

In your example VB6 code it is forcing 0 to be a Long (4 bytes) as it would otherwise be an Integer (2 bytes)

It is the same as doing this long hand approach again VB6 code:

Dim lParam as Long
lParam = 0
ObjFont = SendMessage(hwnd, WM_GETFONT, 0, lParam)

edited May 23 '17 at 10:24

Community

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answered Aug 10 '12 at 14:39

Matt Wilko

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So get the device context for zero? What does that mean? I think it's trying to get a handle to something. – P.Brian.Mackey Aug 10 '12 at 14:41
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@P.Brian.Mackey From MSDN: "If the parameter is NULL it gets the DC for the entire screen" – James Aug 10 '12 at 14:44
And as far as I know a VB6 `Long` is a 32 bit signed integer, e.g. equivalent to a `System.Int32` or using the C# alias `int`. – Martin Liversage Aug 10 '12 at 14:45

score 6 · Answer 2 · answered Aug 10 '12 at 14:45

6

In your specific example, yes, it's equivalent to IntPtr.Zero in C#.

It's the "null handle value" for VB6, that is used by GetDC to return the device context for the entire screen.

answered Aug 10 '12 at 14:45

ken2k

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score 3 · Answer 3 · answered Aug 10 '12 at 14:44

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That's equivalent to passing NULL to GetDC() which instructs the function to return the hDC for the entire screen, so IntPtr.Zero is equivalent.

answered Aug 10 '12 at 14:44

Alex K.

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Nickon · Answer 4 · 2012-08-10T14:49:54.867

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It's the same as Clng(0) :) As the guy below said;D

edited Aug 10 '12 at 14:49

answered Aug 10 '12 at 14:42

Nickon

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In C Yes in VB6 it is the same as `Clng(0)` – Matt Wilko Aug 10 '12 at 14:43
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In C# `0l` is 64 bit. In VB6 `0&` is 32 bit (and `0` is 16 bit). – Martin Liversage Aug 10 '12 at 14:46

What does it mean to GetDC(0&)?

4 Answers4