Regular Expressions and Empty Strings

[cleo]

I'm experimenting with Regular Expressions and Windows Forms.
Frequently I want a value to be either a valid pattern or empty. For
example a Zip code must be 5 digits or may be empty. I know that I can use
the Regular Expression "\d{5}" to test for exactly 5 digits. How can I add
the option for the string to be empty or must I always test the value before
calling the Regular Expression?

Thanks

[Jay B. Harlow [MVP - Outlook]]

Cleo,
Have you tried alternation?

Something like:
Const pattern As String = "^\d{5}$|^$"

The following sites provide a wealth of information on regular expressions.

A tutorial & reference on using regular expressions:
http://www.regular-expressions.info/

The MSDN's documentation on regular expressions:
http://msdn.microsoft.com/library/de...geElements.asp

Hope this helps
Jay

"cleo" <cl**@missinformation.com> wrote in message
news:%2****************@tk2msftngp13.phx.gbl...

I'm experimenting with Regular Expressions and Windows Forms.
Frequently I want a value to be either a valid pattern or empty. For
example a Zip code must be 5 digits or may be empty. I know that I can use the Regular Expression "\d{5}" to test for exactly 5 digits. How can I add the option for the string to be empty or must I always test the value before calling the Regular Expression?

Thanks

[cleo]

Thanks, this expression works. I wasn't aware of the $ expression. The
tutorial references are helpful since I haven't found much just browsing VB
Help.

"Jay B. Harlow [MVP - Outlook]" <Ja************@msn.com> wrote in message
news:u7**************@TK2MSFTNGP11.phx.gbl...

Cleo,
Have you tried alternation?

Something like:
Const pattern As String = "^\d{5}$|^$"

The following sites provide a wealth of information on regular expressions.
A tutorial & reference on using regular expressions:
http://www.regular-expressions.info/

The MSDN's documentation on regular expressions:
http://msdn.microsoft.com/library/de...geElements.asp
Hope this helps
Jay

"cleo" <cl**@missinformation.com> wrote in message
news:%2****************@tk2msftngp13.phx.gbl...

I'm experimenting with Regular Expressions and Windows Forms.
Frequently I want a value to be either a valid pattern or empty. For
example a Zip code must be 5 digits or may be empty. I know that I can

use

the Regular Expression "\d{5}" to test for exactly 5 digits. How can I

add

the option for the string to be empty or must I always test the value

before

calling the Regular Expression?

Thanks