Comparing structs and <null>

  • Thread starter Thread starter Bob Gregory
  • Start date Start date
B

Bob Gregory

Hi all, I'm utter C# newbie, do be gentle.

VS2005 Express refuses point blank to install on my box, so I'm stuck
with C# 1.0 unless someone can point me to a C#2.0 compiler elsewhere.

I have an authentication system rigged up, which is working, but I'd
like to be able to run a test like this

<code>

user thisUser = UserDirectory.GetUserByUsername(Username);
if(thisUser==null){
// user does not exist
}
else{
// do password tests, fetch roles etc.
}

</code>

but the conditional fails 'cos I can't compare type user and <null>.

I've compromised by returning an empty user object and then testing

<code>

if(thisUser.username == null){
// etc. etc.
}

</code>

which works but /smells/ wrong... is there a better way? Will the
nullable types in C# 2.0 let me do this?

Cheers for any advice you can offer,

-- Bob
 
I take it that thisUser is an int or other value type? In that case, no you
can't set it to null.

NullableTypes in CLR 2.0 would be one answer. A magic value is another
possibility, though it offends my sense of elegance (such as it is).

--Bob Grommes
 
Bob,
I'm not sure what the result is in VS 2005, but I beleive that structs
are value types. They can't hold null values. I would just convert the
structure to a class and all of your headaches will be gone. This may not be
the best way, but I think you'll find it pretty easy to implement.
 
Bob,
I suppose you could take a look at overloading operators....but it could
get ugly. Like I said, this is an alternative, but the easier route would be
just to make it a class. Technically a struct is going to be faster than a
class, but lets be honest, it's not going to bring your systems memory to
it's knees.

HTH
 
Lateralus said:
Bob,
I suppose you could take a look at overloading operators....but it could
get ugly.
Click to expand...


That was one of the things I considered, but it did seem a little over
the top for such a simple operation. Out of curiosity, what is the
basic syntax for creating an overloaded operator to test for null?
Like I said, this is an alternative, but the easier route would be
just to make it a class. Technically a struct is going to be faster than a
class, but lets be honest, it's not going to bring your systems memory to
it's knees.
Click to expand...

Yeah, I came to this conclusion 5 minutes after posting, with the aid
of a guide to reference and value types; that's about my average
whenever I post to Google, so I always end up feeling foolish.
Conceptually it's nicer anyway because a user is an object and not a
value, but that's what you get for trying to be clever about
performance.
HTH
Click to expand...

You confirmed what I'd figured out, and you have letters after your
name, so thanks a lot :)


-- Bob
 
Bob,
Here is a link to a discussion that should show you some sample code.
They got around it by creating a "dummy" class, overloading the operators,
as well as the Equals() and GetHashCode() methods. You have to overload the
2 methods just mentioned if you are going to overload the "==" and "!="
comparison operators.

http://groups.google.com/groups?hl=...4%24Ji1.213079%40news20.bellglobal.com&rnum=2

The name of the thread is "c# assign null to a struct". If the link above
doesn't work, just search for that thread on google.
 
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