C# - Using regex with if statements

Question

I have some code that checks a fields input against a regex, although for some reason (no matter what I put in the field, it returns flase. Is there something I have missed?

private void textBox5_Validating(object sender, CancelEventArgs e)
{
    String AllowedChars = @"^a-zA-Z0-9.$";
    if (Regex.IsMatch(textBox5.Text, AllowedChars))
    {
        MessageBox.Show("Valid");
    }
    else
    {
        MessageBox.Show("Invalid");
    }
}

Looks like your reg exp is wrong. It looks to me like it's saying "allow anything except a-zA-Z0-9." — Jamie Dixon
– Jamie Dixon, Commented Jun 20, 2011 at 18:21
"I know I'll use Regex to solve my problem!" Now you have two problems. — asawyer
– asawyer, Commented Jun 20, 2011 at 18:22

naivists · Accepted Answer · 2011-06-20 18:19:44Z

7

The regex makes no sense to me. This one would (notice the square brackets used for defining an alphabet):

String AllowedChars = @"^[a-zA-Z0-9]*$";

answered Jun 20, 2011 at 18:19

naivists

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Comments

Ed Chapel · Accepted Answer · 2011-06-20 18:20:20Z

6

What you want is to group those characters and allow 0 or more:

@"^[a-zA-Z0-9.]*$"

Otherwise, what you posted allows "a-zA-Z0-9" and one more character only.

answered Jun 20, 2011 at 18:20

Ed Chapel

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Comments

Jon · Accepted Answer · 2011-06-20 18:20:24Z

5

Probably incorrect regex. Maybe you meant this:

String AllowedChars = @"^[a-zA-Z0-9]*$";

This would allow any number (including none) of alphanumeric chars. I have removed the period (which matches any character) because it does not make much sense in this context.

answered Jun 20, 2011 at 18:20

Jon

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1 Comment

Tadmas Over a year ago

The period may have been intended to be a literal period character rather than a metacharacter (perhaps "www.example.com" is a valid input), especially considering the variable name of AllowedChars. In that case, it should be included within the square brackets.

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