J
John A Grandy
do these mean the same thing ?
Dim s As String
.....
If s Is Nothing Then
.....
If s = Nothing Then
.....
Dim s As String
.....
If s Is Nothing Then
.....
If s = Nothing Then
.....
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T
Trev Hunter
Yes and no....
-----------------------------------
Dim s as String
Debug.WriteLine(s is Nothing) ' True
Debug.WriteLine(s = Nothing) ' True
Debug.WriteLine(s = "") ' True
s = "" ' Same as s = String.Empty
Debug.WriteLine(s is Nothing) ' False
Debug.WriteLine(s = Nothing) ' True
------------------------------------
"s = Nothing" tests to see if it is not assigned to anything OR is equal to
""
"s is nothing" only tests to see if it is not assigned to anything
i.e.
--------------------------
If s = nothing then
.....
' is equlvelent to
If s is nothing orelse s = String.Empty then
....
--------------------------
If you want short code to test for empty strings, use
If s = "" then
but beware of performance if doing this in a big loop because of string
comparisons. The following may have a slight performance advantage:
If s is nothing orelse s.Length = 0 then
HTH,
Trev.
-----------------------------------
Dim s as String
Debug.WriteLine(s is Nothing) ' True
Debug.WriteLine(s = Nothing) ' True
Debug.WriteLine(s = "") ' True
s = "" ' Same as s = String.Empty
Debug.WriteLine(s is Nothing) ' False
Debug.WriteLine(s = Nothing) ' True
------------------------------------
"s = Nothing" tests to see if it is not assigned to anything OR is equal to
""
"s is nothing" only tests to see if it is not assigned to anything
i.e.
--------------------------
If s = nothing then
.....
' is equlvelent to
If s is nothing orelse s = String.Empty then
....
--------------------------
If you want short code to test for empty strings, use
If s = "" then
but beware of performance if doing this in a big loop because of string
comparisons. The following may have a slight performance advantage:
If s is nothing orelse s.Length = 0 then
HTH,
Trev.
C
Cor
Hi John,
No
Try this
\\\
Dim s As String
If s Is Nothing Then MessageBox.Show("IsNothing")
If s = Nothing Then MessageBox.Show("=Nothing")
s = ""
If s Is Nothing Then MessageBox.Show("IsNothing2")
'Isnothing 2 Will not be showed
If s = Nothing Then MessageBox.Show("=Nothing2")
'=Nothing is true
//
I hope this helps?
Cor
No
Try this
\\\
Dim s As String
If s Is Nothing Then MessageBox.Show("IsNothing")
If s = Nothing Then MessageBox.Show("=Nothing")
s = ""
If s Is Nothing Then MessageBox.Show("IsNothing2")
'Isnothing 2 Will not be showed
If s = Nothing Then MessageBox.Show("=Nothing2")
'=Nothing is true
//
I hope this helps?
Cor
J
John A Grandy
<<<
The following may have a slight performance advantage:
If s is nothing orelse s.Length = 0 then
why not use
If s = Nothing Then
The following may have a slight performance advantage:
If s is nothing orelse s.Length = 0 then
why not use
If s = Nothing Then
T
Trev Hunter
why not use
Because if s is not nothing, then a string comparison is done to check if it
is equal to "" wich is slower than checking the length.
If s = Nothing Then
is the same as
If s is Nothing orelse s = "" Then
where as if you use
If s is Nothing orelse s.Length=0 Then
you cut out the s = "" string comparison.
The performance advantage is really small though and will unlikley make any
difference in a real world application (on my machine it averages out about
1/50 sec for 200000 iterations).
HTH,
Trev.
If s = Nothing Then
Because if s is not nothing, then a string comparison is done to check if it
is equal to "" wich is slower than checking the length.
If s = Nothing Then
is the same as
If s is Nothing orelse s = "" Then
where as if you use
If s is Nothing orelse s.Length=0 Then
you cut out the s = "" string comparison.
The performance advantage is really small though and will unlikley make any
difference in a real world application (on my machine it averages out about
1/50 sec for 200000 iterations).
HTH,
Trev.
H
Herfried K. Wagner [MVP]
* "John A Grandy said:do these mean the same thing ?
Dim s As String
....
If s Is Nothing Then
....
If s = Nothing Then
....
In addition to the other replies -- you can query old messages of this
group using Google Groups Search (<http://www.deja.com>). Just select
this group (microsoft.public.dotnet.languages.vb) in the advanced groups
search and "feed" Google with the keywords. I remember there were some
threads about this topic in the past.