Why IsNumeric("5-") is true?

[Guest]

Can anybody tell why IsNumeric("5-") is true?

 

[Cor Ligthert [MVP]]

Tony,

Why not, that is common here, be aware that this method is to check strings
from textboxes

Cor

 

[Patrice]

This is a legacy VB/VBA function that returns true if the value *starts*
with something usable (working in conjonction with Val that will properly
convert something that starts with a number).

If you want to be strict on possible values, it is best to use other
functions such as TryParse...

 

[Stephany Young]

Maybe you could tell us why you thingk it shouldn't be.

 

[Guest]

Patrice,

That is not how IsNumeric works.

If it did work that way then, for example, IsNumeric("5B") would return
True, but it returns False.

Kerry Moorman

 

[Andrew Morton]

Can anybody tell why IsNumeric("5-") is true?

It represents a number just less than 5, like 5+ represents a number just
greater than 5.

For example, you might encounter something like "the limit of 1/x as x->0-
...." (where -> is meant to represent an arrow) which means the limit of 1/x
as x approaches zero from the negative side.

See it written as a superscript at http://mathworld.wolfram.com/Limit.html
(amusing cartoon at end of page, too

Andrew

 

[Patrice]

Good point. I probably forgot how it works exactly. The bottom line is that
this function can return true in some cases even if the "number" is not
strictly a number so your best bet is to use another function that does a
more strict checking...

P.S. I finally gave it a try using the following code :

Dim a() As String = {"&h5", "5?", "5 6"} ' Use your own currency
symbol instead of ?
Dim r As Integer
For i As Integer = 0 To UBound(a)
Debug.WriteLine(String.Format("{0},{1},{2}", a(i),
IsNumeric(a(i)), Integer.TryParse(a(i), r)))
Next

Results are :

&h5,True,False
5?,True,False
5 6,True,False

As you can see IsNumeric is not as picky than TryParse (and was already in
VB/VBA so they likely kept this unchanged for compatibility)...

 

[Guest]

Thanks, Andrew.
I guess you are right. Even I can not find it from VB reference.

Tony

 

[Guest]

In fact, if I try to CInt("5-"), I will get -5. So I guess VB treat it as -5. ?

 

[Stephany Young]

We are really interested to know what you why it shouldn't be interpreted
as -5.