MatchCollection Class

The collection is immutable (read-only) and has no public constructor. The Regex.Matches method returns a MatchCollection object.

The collection contains zero or more System.Text.RegularExpressions.Match objects. If the match is successful, the collection is populated with one System.Text.RegularExpressions.Match object for each match found in the input string. If the match is unsuccessful, the collection contains no System.Text.RegularExpressions.Match objects, and its Count property equals zero.

When applying a regular expression pattern to a particular input string, the regular expression engine uses either of two techniques to build the MatchCollection object:

• Direct evaluation.

  The MatchCollection object is populated all at once, with all matches resulting from a particular call to the Regex.Matches method. This technique is used when the collection's Count property is accessed. It typically is the more expensive method of populating the collection and entails a greater performance hit.

• Lazy evaluation.

  The MatchCollection object is populated as needed on a match-by-match basis. It is equivalent to the regular expression engine calling the Regex.Match method repeatedly and adding each match to the collection. This technique is used when the collection is accessed through its GetEnumerator method, or when it is accessed using the foreach statement (in C#) or the For Each...Next statement (in Visual Basic).

To iterate through the members of the collection, you should use the collection iteration construct provided by your language (such as foreach in C# and For Each…Next in Visual Basic) instead of retrieving the enumerator that is returned by the GetEnumerator method.

The following example illustrates the use of the MatchCollection class to interrogate a set of Match instances.

using System;
using System.Text.RegularExpressions;

public class Test
{

    public static void Main ()
    {

        // Define a regular expression for repeated words.
        Regex rx = new Regex(@"\b(?<word>\w+)\s+(\k<word>)\b",
          RegexOptions.Compiled | RegexOptions.IgnoreCase);

        // Define a test string.        
        string text = "The the quick brown fox  fox jumped over the lazy dog dog.";

        // Find matches.
        MatchCollection matches = rx.Matches(text);

        // Report the number of matches found.
        Console.WriteLine("{0} matches found in:\n   {1}", 
                          matches.Count, 
                          text);

        // Report on each match.
        foreach (Match match in matches)
        {
            GroupCollection groups = match.Groups;
            Console.WriteLine("'{0}' repeated at positions {1} and {2}",  
                              groups["word"].Value, 
                              groups[0].Index, 
                              groups[1].Index);
        }

    }
	
}
// The example produces the following output to the console:
//       3 matches found in:
//          The the quick brown fox  fox jumped over the lazy dog dog.
//       'The' repeated at positions 0 and 4
//       'fox' repeated at positions 20 and 25
//       'dog' repeated at positions 50 and 54

.NET Framework

.NET Framework Client Profile

Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference