Programming Visual Basic 2005

Regular Expressions

Often a simple value or range check is insufficient; you must check that the form of the data entered is correct. For example, you may need to ensure that a ZIP code is five digits, an email address is in the form [e-mail], a credit card matches the right format, and so forth.

A RegularExpressionValidator allows you to validate that a text field matches a regular expression. Regular expressions are a language for describing and manipulating text.

Tip

For more complete coverage of regular expressions , please see Mastering Regular Expressions, Second Edition, by Jeffrey Friedl (O'Reilly). For a wonderful tool that will help you create, understand, and master regular expressions, take a look at RegEx buddy available at http://www.regexbuddy.com.

A regular expression consists of two types of characters: literals and metacharacters . A literal is just a character you wish to match in the target string. A metacharacter is a special symbol that acts as a command to the regular expression parser. The parser is the engine responsible for understanding the regular expression. Consider this regular expression:

    ^\d{5}$

This will match any string that has exactly five numerals. The initial metacharacter, ^, indicates the beginning of the string. The second metacharacter, \d, indicates a digit. The third metacharacter, {5}, indicates exactly five of the digits, and the final metacharacter, $, indicates the end of the string. Thus, this Regular Expression matches five ...