C# 5.0 Programmer's Reference

Chapter 21 Regular Expressions

What’s in This Chapter

• Regular expression syntax
• Using regular expressions to detect matches, find matches, and make replacements
• Using regular expressions to parse input

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Many applications enable the user to type information but the information should match some sort of pattern. For example, the string 784-369 is not a valid phone number and Rod@Stephens@C#Helper.com is not a valid e-mail address.

One approach for validating this kind of input is to use string methods. You could use the string class’s IndexOf, LastIndexOf, Substring, and other methods to break the input apart and see if the pieces make sense. For all but the simplest situations, however, that would be a huge amount of work.

Regular expressions provide another method for verifying that the user’s input matches a pattern. A regular expression is a string that contains characters that define a pattern. For example, the regular expression ^\d{3}-\d{4}$ represents a pattern that matches three digits followed by a hyphen followed by four more digits as in 123-4567. (This isn’t a great pattern for matching U.S. phone numbers because it enables many invalid combinations such as 111-1111 and 000-0000.)

The .NET Framework includes classes that can use ...