CODEWITHSUNDEEP
asp.net
sergioramosiker
sergioramosiker

Reputation: 375

Allow only alphanumeric character

i want to allow only alphanumeric password i have written following code to match the same but the same is not working

Regex.IsMatch(txtpassword.Text, "^[a-zA-Z0-9_]*$") never return false even if i type password test(which do not contain any number).

ElseIf Regex.IsMatch(txtpassword.Text, "^[a-zA-Z0-9_]*$") = False Then
 div_msg.Attributes.Add("class", "err-msg")
 lblmsg.Text = "password is incorrect"

I have tried this also
Dim r As New Regex("^[a-zA-Z0-9]+$")
Dim bool As Boolean
bool = r.IsMatch(txtpassword.Text) and for txtpassword.Text = '4444' , bool is coming true i dont know what is wrong.

Upvotes: 0

Views: 1060

Answers (3)

Mike Perrenoud
Mike Perrenoud

Reputation: 67918

So based on the Regex that you have in the question, it appears you want a password with one lower-case and upper-case letter, one number, and an _; so here is a Regex that will do that:

(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*_).{4,8}

Regular expression visualization

Debuggex Demo

The {4,8} indicates the length of the password; you can set that accordingly.

Upvotes: 1

Merlin Denker
Merlin Denker

Reputation: 1418

Try the following Expression:

([^a-zA-Z0-9]+)

This will match if your Password contains any character that is not alphanumeric. If you get a match, do your error handling.

Upvotes: 1

DTH
DTH

Reputation: 11

First of all, the '_' is not a valid alpha-numeric character. See http://en.wikipedia.org/wiki/Alphanumeric

And, second, take another look at your regular expression.

[a-zA-Z0-9_]*

This can match 0 OR more alpha-numeric characters or 0 OR more '_' characters. Using this pattern, a password '&#&#^$' would return TRUE.

You probably want to test for 1 OR more characters that ARE NOT an alpha-numeric. If that test returns TRUE, then throw the error.

Hope this helps.

Upvotes: 1

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