November 1, 2013

Regular Expression's Technique and Methods

Regular expressions are a good way to validate text fields such as names, addresses, phone numbers, and other user information. You can use them to constrain input, apply formatting rules, and check lengths. To validate input captured with server controls, you can use the RegularExpressionValidator control. To validate other forms of input, such as query strings, cookies, and HTML control input, you can use the System.Text.RegularExpressions.Regex class.


To validate a server control's input using a RegularExpressionValidator

  • Add a RegularExpressionValidator control to your page.
  • Set the ControlToValidate property to indicate which control to validate.
  • Set the ValidationExpression property to an appropriate regular expression.
  • Set the ErrorMessage property to define the message to display if the validation fails.
The following example shows a RegularExpressionValidator control used to validate a name field.

<%@ language="C#" %>
<form id="form1" runat="server">
    <asp:TextBox ID="txtName" runat="server"/>
    <asp:Button ID="btnSubmit" runat="server" Text="Submit" />
    <asp:RegularExpressionValidator ID="regexpName" runat="server"     
                                    ErrorMessage="This expression does not validate." 
                                    ValidationExpression="^[a-zA-Z'.\s]{1,40}$" />

Regex Class

If you are not using server controls or if you need to validate input from sources other than form fields, such as query string parameters or cookies, you can use the Regex class within the System.Text.RegularExpressions namespace. To use the Regex class:

1. Add a using statement to reference the System.Text.RegularExpressions namespace.
2. Call the IsMatch method of the Regex class, as shown in the following example.

// Instance method:
Regex reg = new Regex(@"^[a-zA-Z'.]{1,40}$");

// Static method:
if (!Regex.IsMatch(txtName.Text, 
  // Name does not match schema

Regular Expression Comments

Regular expressions are much easier to understand if you use the following syntax and comment each component of the expression by using a number sign (#). To enable comments, you must also specify RegexOptions.IgnorePatternWhitespace, which means that non-escaped white space is ignored.

Regex regex = new Regex(@"
                        ^           # anchor at the start
                       (?=.*\d)     # must contain at least one numeric character
                       (?=.*[a-z])  # must contain one lowercase character
                       (?=.*[A-Z])  # must contain one uppercase character
                       .{8,10}      # From 8 to 10 characters in length
                       \s           # allows a space 
                       $            # anchor at the end", 

Common Regular Expressions

FieldExpressionFormat SamplesDescription
Name^[a-zA-Z''-'\s]{1,40}$John Doe
Validates a name. Allows up to 40 uppercase and lowercase characters and a few special characters that are common to some names. You can modify this list.
Social Security Number^\d{3}-\d{2}-\d{4}$111-11-1111Validates the format, type, and length of the supplied input field. The input must consist of 3 numeric characters followed by a dash, then 2 numeric characters followed by a dash, and then 4 numeric characters.
Phone Number^[01]?[- .]?(\([2-9]\d{2}\)|[2-9]\d{2})[- .]?\d{3}[- .]?\d{4}$(425) 555-0123
425 555 0123
Validates a U.S. phone number. It must consist of 3 numeric characters, optionally enclosed in parentheses, followed by a set of 3 numeric characters and then a set of 4 numeric characters.
E-mail^(?("")("".+?""@)|(([0-9a-zA-Z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9a-zA-Z])@))(?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|(([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,6}))$someone@example.comValidates an e-mail address.
URL^(ht|f)tp(s?)\:\/\/[0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*(:(0-9)*)*(\/?)([a-zA-Z0-9\-\.\?\,\'\/\\\+&amp;%\$#_]*)?$ a URL
ZIP Code^(\d{5}-\d{4}|\d{5}|\d{9})$|^([a-zA-Z]\d[a-zA-Z] \d[a-zA-Z]\d)$12345Validates a U.S. ZIP Code. The code must consist of 5 or 9 numeric characters.
Password(?!^[0-9]*$)(?!^[a-zA-Z]*$)^([a-zA-Z0-9]{8,10})$Validates a strong password. It must be between 8 and 10 characters, contain at least one digit and one alphabetic character, and must not contain special characters.
Non- negative integer^\d+$0
Validates that the field contains an integer greater than zero.
Currency (non- negative)^\d+(\.\d\d)?$1.00Validates a positive currency amount. If there is a decimal point, it requires 2 numeric characters after the decimal point. For example, 3.00 is valid but 3.1 is not.
Currency (positive or negative)^(-)?\d+(\.\d\d)?$1.20Validates for a positive or negative currency amount. If there is a decimal point, it requires 2 numeric characters after the decimal point.

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