C# 4 and .NET 4

224 ❘ ChaPTer 9 strinGs And reGulAr expressiOns
that the group in question should not be saved (you only want to save 4355; you don’t need :4355 as well!).
Don’t get confused by the two colons following each other — the first colon is part of the : sequence that
says “don’t save this group,” and the second is text to be searched for.
If you run this pattern on the following string, you’ll get one match: http://www.wrox.com.
Hey I've just found this amazing URI at
http:// what was it --oh yes http://www.wrox.com
Within this match, you will find the three groups just mentioned as well as a fourth group, which represents
the match itself. Theoretically, it is possible that each group itself might return no, one, or more than one
match. Each of these individual matches is known as a capture. So, the first group, (\S+), has one capture,
http. The second group also has one capture (www.wrox.com). The third group, however, has no captures,
because there is no port number on this URI.
Notice that the string contains a second http://. Although
this does match up to the first group, it will not be captured
by the search because the entire search expression does not
match this part of the text.
There isn’t space to show examples of C# code that uses
groups and captures, but you should know that the .NET
RegularExpressions classes support groups and captures
through classes known as Group and Capture. Also,
the GroupCollection and CaptureCollection classes
represent collections of groups and captures. The Match
class exposes the Groups property, which returns
the corresponding GroupCollection object. The Group
class correspondingly implements the Captures property,
which returns a CaptureCollection. The relationship
between the objects is shown in Figure 9-3.
You might not want to return a Group object every time
you just want to group some characters. A fair amount of
overhead is involved in instantiating the object, which is
not necessary if all you want is to group some characters as
part of your search pattern. You can disable this by starting
the group with the character sequence : for an individual
group, as was done for the URI example, or for all groups
by specifying the RegExOptions.ExplicitCaptures flag
on the RegEx.Matches() method, as was done in the
earlier examples.
RegEx
figure 9-3
Matches( )
method
Match( )
method
MatchCollection
Match
GroupCollection
Group
CaptureCollection
Capture
summary
You have quite a number of available data types at your disposal when working with the .NET Framework.
One of the most used types in your applications (especially applications that focus on the submission and
retrieval of data) is the string data type. The importance of string is the reason that this book has a
complete chapter focused on how to use the string data type and manipulate it in your applications.
When working with strings in the past, it was quite common to just slice and dice the strings as needed
using concatenation. With the .NET Framework, you can use the StringBuilder class to accomplish a lot
of this task with better performance than before.
Last, but hardly least, advanced string manipulation using regular expressions is an excellent tool to search
through and validate your strings.
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