Chapter 8: Strings and Regular Expressions

Overview

In the beginning of this book, you have been almost constantly using strings and have taken for granted the stated mapping that the string keyword in C# actually refers to the .NET base class. System.String. System.String is a very powerful and versatile class, but it is by no means the only string-related class in the .NET armory. This chapter starts off by reviewing the features of System.String and then looks at some quite nifty things you can do with strings using some of the other .NET classes - in particular those in the System.Text and System.Text.RegularExpressions namespaces. This chapter covers the following areas:

• Building strings - If you’re performing repeated modifications on a string, for example in order to build up a lengthy string prior to displaying it or passing it to some other method or application, the String class can be very inefficient. For this kind of situation, another class, System.Text.StringBuilder is more suitable, because it has been designed exactly for this situation.

• Formatting expressions - You also take a closer look at those formatting expressions that have been used in the Console.WriteLine() method throughout these last few chapters. These formatting expressions are processed using a couple of useful interfaces, IFormatProvider and IFormattable, and by implementing these interfaces on your own classes, you can actually define your own formatting sequences so that Console.WriteLine() and similar classes will display the values of your classes in whatever way you specify.

• Regular expressions - .NET also offers some very sophisticated classes that deal with the situation in which you need to identify or extract substrings that satisfy certain fairly sophisticated criteria; for example, finding all occurrences within a string where a character or set of characters is repeated, finding all words that begin with s and contain at least one n, or strings that adhere to employee ID or Social Security number constructions. Although you can write methods to perform this kind of processing using the String class, such methods are cumbersome to write. Instead, you can use some classes from System.Text .RegularExpressions, which are designed specifically to perform this kind of processing.