Question

I tried to implement the IP address validation using Required filed validator but it doesn’t seem to work its displaying error “Unrecognized Escape Sequence”

<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" 
                            ControlToValidate="txtadapterid" ErrorMessage="Please Enter a Valid IP Address" 
                            Font-Size="Small" 
                            ValidationExpression="^(([01]?\d\d?|2[0-4]\d|25[0-5])\.){3}([01]?\d\d?|25[0-5]|2[0-4]\d)$"></asp:RegularExpressionValidator>

and the code file method is

   private void checkRejex(string strFindin)
{
    Regex myRegex = new Regex("^(([01]?\d\d?|2[0-4]\d|25[0-5])\.){3}([01]?\d\d?|25[0-5]|2[0-4]\d)$");
    if (myRegex.IsMatch(strFindin))
    {
        lblmsg.Text = "Valid Input";
        lblmsg.ForeColor = Color.Green;
    }
    else
    {
        lblmsg.Text = "Please enter a valid IP Address";
        lblmsg.ForeColor = Color.Red;
    }
}

Answer 1

Rather than a plain string with backslashes, as you have:

new Regex("^(([01]?\d\d?|2[0-4]\d|25[0-5])\.){3}([01]?\d\d?|25[0-5]|2[0-4]\d)$")

you need to use a Verbatim String, prefixed with an @, like this:

new Regex(@"^(([01]?\d\d?|2[0-4]\d|25[0-5])\.){3}([01]?\d\d?|25[0-5]|2[0-4]\d)$")

The @ prevents the backslashes being interpreted as part of the string, but instead causes them to be passed through to the Regex as you intended.

See String literals in the documentation for full details.