string == and Equals

[Peter K]

Hi

Is there any way that the following to statements could give different
results?

I have 2 strings (s1 and s2), which if I compare with == are not equal, but
if I compare with string.Equals, then they are equal.

string.Equals(s1, s2) is true

s1 == s2 is false
All this happens really deep down in an application I am testing. So I
haven't yet worked out what is going on, I'd just like a bit of sanity
feedback (I always though that == and Equals on strings were the same).
Thanks,
Peter

[Peter K]

Peter K <xd****@hotmail.comwrote in
news:eC**************@TK2MSFTNGP05.phx.gbl:

Is there any way that the following to statements could give different
results?

I have 2 strings (s1 and s2), which if I compare with == are not
equal, but if I compare with string.Equals, then they are equal.

string.Equals(s1, s2) is true

s1 == s2 is false

I have now found out why. Of course the objects are "objects" not
"strings". Even though they are string values, they are of type object - I
just hadn't seen that.

[Jon Skeet [C# MVP]]

On Jan 24, 11:13 am, Peter K <[e-mail]:

<snip>

string.Equals(s1, s2) is true

s1 == s2 is false

I have now found out why. Of course the objects are "objects" not
"strings". Even though they are string values, they are of type object - I
just hadn't seen that.

I suspect what you mean is that either s1, s2 or both of them are
declared as type object. If they were declared as string variables,
you'd see the correct result.

Jon

[Peter K]

Jon Skeet [C# MVP] <sk***@pobox.comwrote in
news:MP*********************@msnews.microsoft.com:

Peter K <xd****@hotmail.comwrote:

>Yes, both s1 and s2 are of type object.

Are they both known to be strings? If so, that's the easiest way to fix
it - declare them as string variables instead of object variables, and
it'll work fine.

I don't know if they are "always" strings. I don't understand the entirity
of the program, or how it is used :-(

I've sent a begging email to the original programmer, asking about this
(and hoping I can make this simple change), and I hope he replies :-)

Thanks,
Peter

[Marc Gravell]

In that case, try the static "object.Equals(x,y)" method... this tests
for referential equality, and (if not) checks whether they both are
non-null, then uses x.Equals(y)

It is probably your best bet if you don't know the types and aren't
using generics.

Marc

[Ignacio Machin \( .NET/ C# MVP \)]

Hi,
A dirty workaround is trying to convert them to string:
string s = o as string;

string s1 = o1 as string;

and then check if any of them is null, if so at least one of them was not
an string
--
Ignacio Machin
http://www.laceupsolutions.com
Mobile & warehouse Solutions.
"Peter K" <xd****@hotmail.comwrote in message
news:%2***************@TK2MSFTNGP06.phx.gbl...

Jon Skeet [C# MVP] <sk***@pobox.comwrote in
news:MP*********************@msnews.microsoft.com:

>Peter K <xd****@hotmail.comwrote:

>>Yes, both s1 and s2 are of type object.

Are they both known to be strings? If so, that's the easiest way to fix
it - declare them as string variables instead of object variables, and
it'll work fine.

I don't know if they are "always" strings. I don't understand the entirity
of the program, or how it is used :-(

I've sent a begging email to the original programmer, asking about this
(and hoping I can make this simple change), and I hope he replies :-)

Thanks,
Peter

[Peter Duniho]

On Thu, 24 Jan 2008 03:21:01 -0800, Jon Skeet [C# MVP] <sk***@pobox.com>
wrote:

I suspect what you mean is that either s1, s2 or both of them are
declared as type object. If they were declared as string variables,
you'd see the correct result.

And please, remind me again, why is it that the == operator doesn't just
automatically use Object.Equals()?

I'm sure there's a good reason, but it's escaping me at the moment. It
seems pretty relevant to the question though.

Pete

[christery]

I'm sure there's a good reason, but it's escaping me at the moment. *It *

seems pretty relevant to the question though.

Pete

Oh you men that theae are too red cars and you ask
are both cars red? = true
are they the same car?= false
//CY

[Jon Skeet [C# MVP]]

On Jan 25, 9:20 am, [e-mail] wrote:

<snip>

Well It wont work with reserved words (I think)... didnt try it but
pretty shure, == and != arent reserved as I remember.. just operators
and operators can be overloaded

Yes, but that's just begging Peter's question as to *why* they can be
overloaded, rather than the compiler just generating code which calls
object.Equals(x, y). Reference equality is rarely useful (and can be
explicitly checked with object.ReferenceEquals).

Overloading == is nice for value types of course, as it avoids boxing.

For reference types, I suspect there aren't many situations where
you'd want == and != to behave differently to a call to object.Equals.
I suppose it avoids a virtual call, which could be slightly handy in
terms of performance... on the other hand, it *makes* the call non-
virtual, which can be a pain. Mind you, equality comparisons up and
down a type hierarchy are painful anyway.

Jon

[christery]

Yeah but for mocking up a project if you get pissed this is great...
the wow/ick code shows just what (has been sold out by) letting
operators to be overloaded causes

still I think there is the q
is two cars red
and is those the same car?
are we looking at values or references...

But Im not too shure I understood the q.

Think my english is mysterius? I can answwe in mienkieli instead...

//CY Who tooh away chr$(12)?