C# 4 and .NET 4

9strings and regular expressions
WhaT ’ s in This ChaPTer
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Building strings
Formatting expressions
Using regular expressions
Since the beginning of this book, you have been using strings almost constantly, and might not have
realized that the stated mapping that the string keyword in C# actually refers to is the System
.String .NET base class. 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 by reviewing the features of
System.String and then looks at some 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:
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Building strings — If you ’ re performing repeated modifi cations on a string, for example,
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 ineffi cient. When you fi nd yourself in this kind of
situation, another class, System.Text.StringBuilder , is more suitable because it has been
designed exactly for this situation.
Formatting expressions — This chapter takes a closer look at those formatting expressions that
have been used in the Console.WriteLine() method throughout the past few chapters. These
formatting expressions are processed using a couple of useful interfaces, IFormatProvider
and IFormattable . By implementing these interfaces on your own classes, you can actually
defi ne 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
situations in which you need to identify or extract substrings that satisfy certain fairly
sophisticated criteria; for example, fi nding all occurrences within a string where a character or
set of characters is repeated, fi nding all words that begin with “ s ” and contain at least one “ n ,”
or strings that adhere to an employee ID or a Social Security number construction. Although
you can write methods to perform this kind of processing using the String class, such methods
are cumbersome to write. Instead, you will fi nd that some classes, specifi cally those from
System.Text.RegularExpressions , are designed to perform this kind of processing.
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