Strange bug: condition true in IF statement, false the next statement

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G

Guest

Hi

I'm facing a very strange problem here. My code looks like this

if(A == null
return
doSomethingWith(A.b)

When I run my code (in debug mode), I get a NullReferenceException -- and on breaking, I discover that A is indeed null. (The exception is raised in the doSomethingWith line.

How can this be? No code has been executed between the IF statement and the next statement. In the context I run the code, A *shouldn't* be null, and even if it were - why does it not step into the IF statement and return

What's worse, when I set a breakpoint anywhere near this segment in my code, the problem *disappeaers* -- A isn't null, and everything works properly

This looks like the classic '=' instead of '==' mistake I'm used to from C++, but that's not the case here (I checked, and anyway C# IF statements require bool...). The fact that it disappears on extensive debugging makes me think it's some sort of debugger/runtime-environment bug. I thought it might be related to garbage collection, but that doesn't make sense either (since I have a reference to A, it shouldn't be collected, right?)

Does anyone have any idea what's going wrong

(For completeness' sake, I should mention that the code I'm running was developed for the 1.0 Framework, and I'm now running it with 1.1.)
 
Hi,

we some times have the identical behaviour. It looks like a bug in if-
statement.
I'm realy sure, that there ist no threading issue, because it also
happens to local variables. But i never could reproduce the situation in
sample programs.
It happens on one maschin, but not on another one.

Bye, Jan
 
No, my application is single-threaded; also, unlike the
poster who responded, my bug is deterministic - it *always*
happens, on *every* machine we tried it on...
-----Original Message-----
Hi,

I'm facing a very strange problem here. My code looks like this:

if(A == null)
return;
doSomethingWith(A.b);

When I run my code (in debug mode), I get a
Click to expand...
NullReferenceException -- and on breaking, I discover that
A is indeed null. (The exception is raised in the
doSomethingWith line.)
How can this be? No code has been executed between the IF
Click to expand...
statement and the next statement. In the context I run the
code, A *shouldn't* be null, and even if it were - why does
it not step into the IF statement and return?
What's worse, when I set a breakpoint anywhere near this
Click to expand...
segment in my code, the problem *disappeaers* -- A isn't
null, and everything works properly.
This looks like the classic '=' instead of '==' mistake
Click to expand...
I'm used to from C++, but that's not the case here (I
checked, and anyway C# IF statements require bool...). The
fact that it disappears on extensive debugging makes me
think it's some sort of debugger/runtime-environment bug. I
thought it might be related to garbage collection, but
that doesn't make sense either (since I have a reference to
A, it shouldn't be collected, right?).
Does anyone have any idea what's going wrong?

(For completeness' sake, I should mention that the code
Click to expand...
I'm running was developed for the 1.0 Framework, and I'm
now running it with 1.1.)
 
Do you have a reproducible bit of code you could post here? eg maybe just
the function called from Main().

I'd be happy to have a look at it if you can post some non-working code.

(Trouble is, it sounds either like a silly mistake of the sort we all make
from time to time, or one of those problems that disappears when you try to
isolate it).
 
Sorry, can't post any code -- but it really is much like the fake snippet I posted.

It's not *my* code, either, or even code developed by my company... it appears in the XtraGrid control, developed by DevExpress.
I just checked, and it doesn't happen in Visual Studio.NET 2002 (I used 2003 before) with framework 1.0, so that settles it as far as I'm concerned -- it's a .NET platform bug.
Do you have a reproducible bit of code you could post here? eg maybe just
the function called from Main().

I'd be happy to have a look at it if you can post some non-working code.

(Trouble is, it sounds either like a silly mistake of the sort we all make
from time to time, or one of those problems that disappears when you try to
isolate it).
Click to expand...

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