why is it not possible to compare IntPtr.Zero and default(IntPtr)?

Question

I just learned the hard way that IntPtr.Zero cannot be compared to default(IntPtr). Can someone tell me why?

IntPtr.Zero == new IntPtr(0) -> "could not evaluate expression"
IntPtr.Zero == default(IntPtr) --> "could not evaluate expression"
IntPtr.Zero == (IntPtr)0 -> "could not evaluate expression"

IntPtr.Zero.Equals(IntPtr.Zero) --> "Enum value was out of legal range" exception
IntPtr.Zero.Equals(default(IntPtr)) --> "Enum value was out of legal range" exception

IntPtr.Zero == IntPtr.Zero --> true
new IntPtr(0) == new IntPtr(0) --> true

They compare fine, and they are equal: `var isEqual = IntPtr.Zero == new IntPtr(0);` and isEqual is true. — vcsjones, Jun 06 '12 at 14:06
Works for me. What platform are you on and which framework version? — Botz3000, Jun 06 '12 at 14:06
http://ideone.com/BJqvB `IntPtr.Zero == default(IntPtr)` outputs true. In what context is this? — Kendall Frey, Jun 06 '12 at 14:07
My guess is that you have redefined `IntPtr` in some way. If you click on the different ones and press F12, what happens? — Gabe, Jun 06 '12 at 14:08
A search on the phrase "Enum value was out of legal range" finds plenty of examples - this is a known bug in the Watch window in older Visual Studios. Not an issue in VS2010/VS2012rc. — Damien_The_Unbeliever, Jun 07 '12 at 06:50
Not sure how relevant this is, but the way I remember it is: `IntPtr.Equals` is actually comparing what's being pointed at, rather than the pointer's value itself. That may have something to do with it.... — Carsen Daniel Yates, Jun 11 '12 at 00:13
@Damien_The_Unbeliever, you should go ahead and post this as an Answer so I can +1 is. ;-D — Jesse Chisholm, Jun 17 '12 at 17:48
Works for me in the watch window in Visual Studio 2010. Do you see the same behaviour actually in the code (not in the watch window)? — tymtam, Jun 22 '12 at 05:35

jpe · Accepted Answer · 2012-06-24T20:29:08.973

Works for me in compiled code in VS 2010, VS 2008, VS 2005 SP1, Mono 1.2.6. Managed to reproduce both problems in the watch window of Visual Studio 2005 only (I tried with VS 2005 SP1), the compiled code works as expected. (By both problems I mean Problem 1: "Could not evaluate expression", Problem 2: "Enum value was out of legal range".) Thus, as was pointed out by some of the comment authors, it is a VS 2005 watch window bug that you stumbled upon. It is surprisingly hard to quickly find a link to the relevant bug report...

Otherwise in such cases I'd start from reflection to see what types you try to compare (replace Console.Out with any meaningful stream you have access to):

Console.WriteLine("new IntPtr(0) type is: " + new IntPtr(0).GetType());
Console.WriteLine("IntPtr.Zero type is: " + IntPtr.Zero.GetType());

why is it not possible to compare IntPtr.Zero and default(IntPtr)?

1 Answers1