Is there a test for an empty string that returns a boolean?
 

Hi

I'm passing the ElevCptn parameter as Optional:

Private Sub SetOptBut(FontBack As Boolean, PlnCptn As String, Optional
ElevCptn As String)

I want to test to see if the parameter has been included & Enable a
button if it is, & Disable it if is isn't, so I'd like it to return a
boolean.

Something like this:
CboElevation.Enabled = IsEmpty(ElevCptn)

Except that doesn't work because "" isn't an empty string.

Any help is appreciated

Ta
Dave F.

Is there a test for an empty string that returns a boolean?
 

On Fri, 09 May 2008 19:01:36 +0100, "Dave F." wrote:

Hi

I'm passing the ElevCptn parameter as Optional:

Private Sub SetOptBut(FontBack As Boolean, PlnCptn As String, Optional
ElevCptn As String)

I want to test to see if the parameter has been included & Enable a
button if it is, & Disable it if is isn't, so I'd like it to return a
boolean.

Something like this:
CboElevation.Enabled = IsEmpty(ElevCptn)

Except that doesn't work because "" isn't an empty string.

Any help is appreciated

Ta
Dave F.

how about Len(ElevCptn) = 0

--ron

Is there a test for an empty string that returns a boolean?
 

You might look at IsMissing, however with your optional string I'd do it
like this

Private Sub SetOptBut(FontBack As Boolean, PlnCptn As String, _
Optional ElevCptn As String = "dummy")

bMissing = (ElevCptn = "dummy")

change "dummy" to something you know will never be passed

Regards,
Peter T


"Dave F." wrote in message
...
Hi

I'm passing the ElevCptn parameter as Optional:

Private Sub SetOptBut(FontBack As Boolean, PlnCptn As String, Optional
ElevCptn As String)

I want to test to see if the parameter has been included & Enable a
button if it is, & Disable it if is isn't, so I'd like it to return a
boolean.

Something like this:
CboElevation.Enabled = IsEmpty(ElevCptn)

Except that doesn't work because "" isn't an empty string.

Any help is appreciated

Ta
Dave F.

Is there a test for an empty string that returns a boolean?
 

"Dave F." wrote in message
...

CboElevation.Enabled = IsEmpty(ElevCptn)

IsEmpty() isn't for strings, it's for Variants that haven't been assigned a
value. IsMissing(), as Peter suggested, is only for Variants. Optional
parameters typed as anything besides a Variant that aren't given a default
value in the procedure declaration get the default for the data type, so
numbers get 0 and strings get empty strings. Therefore you should simply be
able to test ElevCptn against "". Did you ever try that?

Ron's Len() suggestion is also valid.

Is there a test for an empty string that returns a boolean?
 

CboElevation.Enabled = IsEmpty(ElevCptn)

IsEmpty() isn't for strings, it's for Variants that haven't been assigned
a value. IsMissing(), as Peter suggested, is only for Variants. Optional
parameters typed as anything besides a Variant that aren't given a default
value in the procedure declaration get the default for the data type, so
numbers get 0 and strings get empty strings. Therefore you should simply
be able to test ElevCptn against "". Did you ever try that?

Ron's Len() suggestion is also valid.

And to follow up on Jeff's comment, while this may look "simpler"...

CboElevation.Enabled = (ElevCptn = "")

due to the way VB stores Strings, this is marginally faster...

CboElevation.Enabled = (Len(ElevCptn) = 0)

It wouldn't matter in a single or few usage situation; but, inside a very
large loop, it could make a difference.

Rick

Is there a test for an empty string that returns a boolean?
 

I guess it depends on the OP's overall objective "I want to test to see if
the parameter has been included" and whether "included" means passed or
empty. The way I see it Len(arg) merely tests if the argument contains any
characters, or indeed is an empty string. It doesn't prove either way if the
optional argument was passed or 'is missing'.

Sub test()
Dim a As String, b As String
Call foo(a, b)
MsgBox a & vbCr & b, , "neither arg was missing"

End Sub

Function foo(Optional arg1 As String, Optional arg2 As String = "dummy")

If Len(s1) = 0 Then
arg1 = "arg1 was missing"
Else
arg1 = "return string 1"
End If

If s2 = "dummy" Then
arg2 = "arg2 was missing"
Else
arg2 = "return string 2"
End If

End Function

Regards,
Peter T

"Rick Rothstein (MVP - VB)" wrote in
message ...
CboElevation.Enabled = IsEmpty(ElevCptn)

IsEmpty() isn't for strings, it's for Variants that haven't been
assigned
a value. IsMissing(), as Peter suggested, is only for Variants. Optional
parameters typed as anything besides a Variant that aren't given a
default
value in the procedure declaration get the default for the data type, so
numbers get 0 and strings get empty strings. Therefore you should simply
be able to test ElevCptn against "". Did you ever try that?

Ron's Len() suggestion is also valid.

And to follow up on Jeff's comment, while this may look "simpler"...

CboElevation.Enabled = (ElevCptn = "")

due to the way VB stores Strings, this is marginally faster...

CboElevation.Enabled = (Len(ElevCptn) = 0)

It wouldn't matter in a single or few usage situation; but, inside a very
large loop, it could make a difference.

Rick

Is there a test for an empty string that returns a boolean?
 

Peter T wrote:
I guess it depends on the OP's overall objective "I want to test to see if
the parameter has been included" and whether "included" means passed or
empty. The way I see it Len(arg) merely tests if the argument contains any
characters, or indeed is an empty string. It doesn't prove either way if the
optional argument was passed or 'is missing'.

Hi Peter

You're tight. It appears that even if it isn't passed, the variable is stored as an empty string ("")
For my routine Len(arg) is what I want. I assumed its results could be used within an If Then statement.
I've learnt something new today.

Thank You to all who replied.

Ta
Dave F.