Why is an uninitialised string not empty?

[Dylan Parry]

Hi folks,

I came across something strange a few moments ago when testing some
strings.

In my application a particular object has a name and a title, and is
displayed on a webpage thusly:

Object name - title

But the " - title" bit is only displayed, obviously, if it is
appropriate, ie. a title has been set for that object. I attempted to
achieve that by testing with:

if (myObject.Title != string.Empty) {
...
}

Yet this didn't work as the Title property was returning 'null'. So it
got me wondering, why is 'null != string.Empty' when the 'null' value
belongs to an object of type string?

--
Dylan Parry
http://webpageworkshop.co.uk -- FREE Web tutorials and references

[Sericinus hunter]

Dylan Parry wrote:

[...]

why is 'null != string.Empty' when the 'null' value
belongs to an object of type string?

Because string is a reference type, reference being null means
it does not have any object associated with it. string.Empty is a value
of a concrete object.

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

Hi,

string.Empty has a value, an empty string ( "" ) .

null is the absence of a value.

They are different things.

"Dylan Parry" <us****@dylanparry.com> wrote in message
news:52**************@dylanparry.com...

Hi folks,

I came across something strange a few moments ago when testing some
strings.

In my application a particular object has a name and a title, and is
displayed on a webpage thusly:

Object name - title

But the " - title" bit is only displayed, obviously, if it is
appropriate, ie. a title has been set for that object. I attempted to
achieve that by testing with:

if (myObject.Title != string.Empty) {
...
}

Yet this didn't work as the Title property was returning 'null'. So it
got me wondering, why is 'null != string.Empty' when the 'null' value
belongs to an object of type string?

--
Dylan Parry
http://webpageworkshop.co.uk -- FREE Web tutorials and references

[José Joye]

By the way, if you are using .NET 2.0, you can use the
String.IsNullOrEmpty() method instead of checking for NOT null && not empty

- José
"Dylan Parry" <us****@dylanparry.com> a écrit dans le message de news:
52**************@dylanparry.com...

Hi folks,

I came across something strange a few moments ago when testing some
strings.

In my application a particular object has a name and a title, and is
displayed on a webpage thusly:

Object name - title

But the " - title" bit is only displayed, obviously, if it is
appropriate, ie. a title has been set for that object. I attempted to
achieve that by testing with:

if (myObject.Title != string.Empty) {
...
}

Yet this didn't work as the Title property was returning 'null'. So it
got me wondering, why is 'null != string.Empty' when the 'null' value
belongs to an object of type string?

--
Dylan Parry
http://webpageworkshop.co.uk -- FREE Web tutorials and references

[Dylan Parry]

Josòzoye wrote:

By the way, if you are using .NET 2.0, you can use the
String.IsNullOrEmpty() method instead of checking for NOT null && not empty

Oh that's good :) I didn't know about that one, but will do a quick
replace tomorrow on all the times I've done this so far.

--
Dylan Parry
http://webpageworkshop.co.uk -- FREE Web tutorials and references

[Claes Bergefall]

"Dylan Parry" <us****@dylanparry.com> wrote in message
news:5q***************@dylanparry.com...

Josòzoye wrote:

By the way, if you are using .NET 2.0, you can use the
String.IsNullOrEmpty() method instead of checking for NOT null && not
empty

Oh that's good :) I didn't know about that one, but will do a quick
replace tomorrow on all the times I've done this so far.

Another interesting thing is that VB.NET behaves different. The following
returns true in VB:
Dim b As Boolean = (String.Empty = Nothing)

If you want to distinguish between an empty string and null in VB.NET you
have to use String.Equals
I sometimes forget this when I switch between languages and this can lead to
some interesting bugs :-)

/claes

[Jon Skeet [C# MVP]]

Claes Bergefall <lo*****@nospam.nospam> wrote:

"Dylan Parry" <us****@dylanparry.com> wrote in message
news:5q***************@dylanparry.com...

Josòzoye wrote:

By the way, if you are using .NET 2.0, you can use the
String.IsNullOrEmpty() method instead of checking for NOT null && not
empty

Oh that's good :) I didn't know about that one, but will do a quick
replace tomorrow on all the times I've done this so far.

Another interesting thing is that VB.NET behaves different. The following
returns true in VB:
Dim b As Boolean = (String.Empty = Nothing)

If you want to distinguish between an empty string and null in VB.NET you
have to use String.Equals
I sometimes forget this when I switch between languages and this can leadto
some interesting bugs :-)

You don't actually have to use String.Equals - you can use "Is":

Imports System

Class Test
Shared Sub Main()
Console.WriteLine (String.Empty = Nothing)
Console.WriteLine (String.Empty Is Nothing)
End Sub
End Class

Wacky, eh?

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