Regular expression for reading positive integers with leading zeros

Question

I have the following TextBox and RegularExpressionValidator

<asp:TextBox ID="txtQuantity" runat="server" MaxLength="7"></asp:TextBox>

<asp:RegularExpressionValidator ID="RegularExpressionValidator1" 
runat="server" ErrorMessage="Enter only positive integer values."
ControlToValidate="txtQuantity" ValidationExpression="^[1-9][0-9]*$"
CssClass="required" Display="Dynamic" />

It is reading all the positive integers properly and giving error messages on wrong entries.

But validation is getting failed when a positive integer preceding with a 0 is entered.

Example: "098", "09" etc

Should I change my regular expression or the logic?

Your regex wont accept `098` `^[1-9][0-9]*$`..it starts with `[1-9]` — vks, Jun 24 '15 at 10:04
@moffeltje I *think* OP doesn't want to accept `0` or empty string. And now after you edit it still accepts `0`, but who knows what OP wants. (BTW, `[0-9][0-9]*` → `[0-9]+`.) — Biffen, Jun 24 '15 at 10:07

Wiktor Stribiżew · Accepted Answer · 2015-06-24T10:14:38.400

You can allow zeros with non-zeros and disallow just zeros (or empty string) with

^(?!0+$)[0-9]+$

See demo

REGEX EXPLANATION:

^ - Start of string (not sure it is necessary, I think the regex is anchored by default, but please check)
(?!0+$) - A negative lookahead that checks if the whole string is not equal to 0 (or 0000)
[0-9]+ - 1 or more digits from 0 to 9 (note that it already does not allow empty string)
$ - End of string (same note as for ^)

Regular expression for reading positive integers with leading zeros

1 Answers1