When "ToString" does not equal "ToString"

[Ayende Rahien]

I've a really strange problem, in some part of my code I compare two
strings (through object), and while I *know* that they equal each
other, and in the watch window they do equal each other, then the
comparision return false.

See here for details:

http://www.ayende.com/Blog/PermaLink...c876a6acb.aspx

[Jochen Kalmbach]

Ayende Rahien wrote:

I've a really strange problem, in some part of my code I compare two
strings (through object), and while I *know* that they equal each
other, and in the watch window they do equal each other, then the
comparision return false.

See here for details:

http://www.ayende.com/Blog/PermaLink...34f-bfe0-39ac8
76a6acb.aspx

The problem is that "strings" are neither reference types nor value types!
They are handled in a special way...

In your case you are comparing object references which might be different!
Either use string.Compare(a, b) or a.CompareTo(b) or a.Equals(b)

--
Greetings
Jochen

My blog about Win32 and .NET
http://blog.kalmbachnet.de/

[Richard Blewett [DevelopMentor]]

The code that is failing is the

if( o == test) ?

well o and test are both typed as object so you are using the System.Object == operator which hands off to System.Object.ReferenceEquals. In other words, the comparison will onyl succeed if o and test are teh same physical object

Regards

Richard Blewett - DevelopMentor
http://staff.develop.com/richardb/weblog

nntp://news.microsoft.com/microsoft.public.dotnet.languages.csharp/<29*************************@posting.google.com>

I've a really strange problem, in some part of my code I compare two
strings (through object), and while I *know* that they equal each
other, and in the watch window they do equal each other, then the
comparision return false.

See here for details:

http://www.ayende.com/Blog/PermaLink...c876a6acb.aspx

---
Incoming mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.771 / Virus Database: 518 - Release Date: 28/09/2004

[microsoft.public.dotnet.languages.csharp]

[Richard Blewett [DevelopMentor]]

Umm, strings are reference types. They are immutable which results in some value like behavior but they are definitely reference types (i.e. allocated on the managed heap, referred to vai a 32 bit reference and are garbage collected.

Regards

Richard Blewett - DevelopMentor
http://staff.develop.com/richardb/weblog

nntp://news.microsoft.com/microsoft.public.dotnet.languages.csharp/<Xn**********************************@207.46.248.1 6>

Ayende Rahien wrote:

I've a really strange problem, in some part of my code I compare two
strings (through object), and while I *know* that they equal each
other, and in the watch window they do equal each other, then the
comparision return false.

See here for details:

http://www.ayende.com/Blog/PermaLink...34f-bfe0-39ac8
76a6acb.aspx

The problem is that "strings" are neither reference types nor value types!
They are handled in a special way...

In your case you are comparing object references which might be different!
Either use string.Compare(a, b) or a.CompareTo(b) or a.Equals(b)

--
Greetings
Jochen

My blog about Win32 and .NET
http://blog.kalmbachnet.de/

---
Incoming mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.771 / Virus Database: 518 - Release Date: 28/09/2004

[microsoft.public.dotnet.languages.csharp]

[Jon Skeet [C# MVP]]

Jochen Kalmbach <no********************@holzma.de> wrote:

Ayende Rahien wrote:

I've a really strange problem, in some part of my code I compare two
strings (through object), and while I *know* that they equal each
other, and in the watch window they do equal each other, then the
comparision return false.

See here for details:

http://www.ayende.com/Blog/PermaLink...34f-bfe0-39ac8
76a6acb.aspx

The problem is that "strings" are neither reference types nor value types!
They are handled in a special way...

That's not true. String is a reference type which overrides operator==.

In what way do you believe they're not reference types?

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Jochen Kalmbach]

Jon Skeet [C# MVP] wrote:

> http://www.ayende.com/Blog/PermaLink...0-434f-bfe0-39
> ac8 76a6acb.aspx

The problem is that "strings" are neither reference types nor value
types! They are handled in a special way...

That's not true. String is a reference type which overrides
operator==.

In what way do you believe they're not reference types?

As Richard explains:
They are immutable which results in some value like behavior but they are
definitely reference types.

--
Greetings
Jochen

My blog about Win32 and .NET
http://blog.kalmbachnet.de/

[Jon Skeet [C# MVP]]

Jochen Kalmbach <no********************@holzma.de> wrote:

The problem is that "strings" are neither reference types nor value
types! They are handled in a special way...

That's not true. String is a reference type which overrides
operator==.

In what way do you believe they're not reference types?

As Richard explains:
They are immutable which results in some value like behavior but they are
definitely reference types.

Right. There's nothing particularly special about string being
immutable though - it's perfectly easy to write your own immutable
reference types, and it's often a good idea.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Pradeep]

Even I had the same problem when I try to compare two strings one from
DataTable and a value in string. Then I found out that one string
contains some extra spaces at the end. So I used Trim and then it
worked. I am nnot sure about your problem. but just for information.

[John Smith]

Have you tried
if(o.Equals(test))

"Ayende Rahien" <ay****@gmail.com> wrote in message
news:29*************************@posting.google.co m...

I've a really strange problem, in some part of my code I compare two
strings (through object), and while I *know* that they equal each
other, and in the watch window they do equal each other, then the
comparision return false.

See here for details:

http://www.ayende.com/Blog/PermaLink...c876a6acb.aspx