Regular Expression Result

The results of the regular expression engine of .NET framework can be accessed by Capture Class, CaptureCollection Class, Group Class, GroupCollection Class, Match Class, MatchCollection Class. Both Match Class and MatchCollection Class are used to represent the object return by the Match Method and Matches Method of Regex Class respectively.

Match Class

Represents the results from a single regular expression match.

[System.Serializable]
public class Match : System.Text.RegularExpressions.Group

Properties

Methods

Remarks

• The Match object is immutable and has no public constructor. An instance of the Match class is returned by the Regex.Match method and represents the first pattern match in a string. Subsequent matches are represented by Match objects returned by the Match.NextMatch method. In addition, a MatchCollection object that consists of zero, one, or more Match objects is returned by the Regex.Matches method.

  If the Regex.Matches method fails to match a regular expression pattern in an input string, it returns an empty MatchCollection object. You can then use a foreach construct in C# or a For Each construct in Visual Basic to iterate the collection.

  If the Regex.Match method fails to match the regular expression pattern, it returns a Match object that is equal to Match.Empty. You can use the Success property to determine whether the match was successful.
• If a pattern match is successful, the Value property contains the matched substring, the Index property indicates the zero-based starting position of the matched substring in the input string, and the Length property indicates the length of matched substring in the input string.

  Because a single match can involve multiple capturing groups, Match has a Groups property that returns the GroupCollection. The Match instance itself is equivalent to the first object in the collection, at Match.Groups[0] (Match.Groups(0) in Visual Basic), which represents the entire match. You can access the captured groups in a match in the following ways:

  • You can iterate the members of the GroupCollection object by using a foreach (C#) or For Each (Visual Basic) construct.
  • You can use the GroupCollection.Item[Int32] property to retrieve groups by the number of the capturing group. Note that you can determine which numbered groups are present in a regular expression by calling the instance Regex.GetGroupNumbers method.
  • You can use the GroupCollection.Item[String] property to retrieve groups by the name of the capturing group. Note that you can determine which named groups are present in a regular expression by calling the instance Regex.GetGroupNames() method.

Applies to

.NET Framework: 4.8, 4.7.2, 4.7.1, 4.7, 4.6.2, 4.6.1, 4.6, 4.5.2, 4.5.1, 4.5, 4.0, 3.5, 3.0, 2.0, 1.1

See also

• MatchCollection
• Regex

MatchCollection Class

Represents the set of successful matches found by iteratively applying a regular expression pattern to the input string.

[System.Serializable]
public class MatchCollection : System.Collections.ICollection

Properties

Methods

Extension Methods

Remarks

• 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.

Applies to

.NET Framework: 4.8, 4.7.2, 4.7.1, 4.7, 4.6.2, 4.6.1, 4.6, 4.5.2, 4.5.1, 4.5, 4.0, 3.5, 3.0, 2.0, 1.1

Examples

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head>
       <title>Sample Page</title>
       <meta http-equiv="Content-Type" content="text/html;charset=utf-8">
       <script runat="server">
           Sub Page_Load()
               Dim xpattern As String = "\w+"
               Dim xstring As String = "01234 67 901 34567 9012 4567890"
               Dim xRegex As Regex = New Regex(xpattern, RegexOptions.IgnoreCase)
               Dim xmatch As Match
               Dim xmatches As MatchCollection
               Dim xmatchstr As String
               xmatchstr = "Given pattern: """ & xpattern & """<br />"
               xmatchstr = xmatchstr & "Given string: """ & xstring & """<br />"
               xmatchstr = xmatchstr & "Result of Regex.Match(string): """
               xmatch = xRegex.Match(xstring)
               xmatchstr = xmatchstr & xmatch.value & """<br />"
               xmatchstr = xmatchstr & "Result of Match.Captures.Count: """
               xmatchstr = xmatchstr & xmatch.Captures.Count & """<br />"
               xmatchstr = xmatchstr & "Result of Match.Groups.Count: """
               xmatchstr = xmatchstr & xmatch.Groups.Count & """<br />"
               xmatchstr = xmatchstr & "Result of Regex.Match(string): """
               xmatchstr = xmatchstr & xRegex.Match(xstring).value & """<br />"
               xmatchstr = xmatchstr & "Result of Regex.Match(string,4): """
               xmatchstr = xmatchstr & xRegex.Match(xstring,4).value & """<br />"
               xmatchstr = xmatchstr & "Result of Regex.Match(string,5): """
               xmatchstr = xmatchstr & xRegex.Match(xstring,5).value & """<br />"
               xmatchstr = xmatchstr & "Result of Regex.Match(string,6): """
               xmatchstr = xmatchstr & xRegex.Match(xstring,6).value & """<br />"
               xmatchstr = xmatchstr & "Result of Regex.Match(string,7): """
               xmatchstr = xmatchstr & xRegex.Match(xstring,7).value & """<br />"
               xmatchstr = xmatchstr & "Result of Regex.Match(string,8,3): """
               xmatchstr = xmatchstr & xRegex.Match(xstring,8,3).value & """<br />"
               xmatchstr = xmatchstr & "Result of Regex.Match(string,9,3): """
               xmatchstr = xmatchstr & xRegex.Match(xstring,9,3).value & """<br />"
               xmatchstr = xmatchstr & "Result of Regex.Match(string,10,3): """
               xmatchstr = xmatchstr & xRegex.Match(xstring,10,3).value & """<br />"
               xmatchstr = xmatchstr & "Result of Regex.Match(string,11,3): """
               xmatchstr = xmatchstr & xRegex.Match(xstring,11,3).value & """<br />"
               xmatchstr = xmatchstr & "Result of Regex.Match(string,12,3): """
               xmatchstr = xmatchstr & xRegex.Match(xstring,12,3).value & """<br />"
               xmatchstr = xmatchstr & "Result of Regex.Match(string,13,3): """
               xmatchstr = xmatchstr & xRegex.Match(xstring,13,3).value & """<br />"
               xmatchstr = xmatchstr & "Result of Regex.Match(string,10,7): """
               xmatchstr = xmatchstr & xRegex.Match(xstring,10,7).value & """<br />"
               xmatchstr = xmatchstr & "Result of Regex.Matches(string,pattern).Count: """
               xmatches = Regex.Matches(xstring,xpattern)
               xmatchstr = xmatchstr & xmatches.Count & """<br />"
               Dim xint As Integer = 0
               xmatchstr = xmatchstr & "Result of Regex.Matches(string,pattern)(xint): ""Value, Index, Length""<br />"
               For Each xmatch in xmatches
               xmatchstr = xmatchstr & "Result of Regex.Matches(string,pattern)("& xint & "): """
               xmatchstr = xmatchstr & xmatch.Value & ", " & xmatch.Index & ", " & xmatch.Length & """<br />"
               xint = xint + 1
               Next
               lbl01.Text = xmatchstr
           End Sub
       </script>
    </head>
    <body>
       <% Response.Write ("<h1>This is a Sample Page of Match, and MatchCollection Classes</h1>") %>
       <p>
           <%-- Set on Page_Load --%>
           <asp:Label id="lbl01" runat="server" />
       </p>
    </body>
</html>

Source/Reference

• https://docs.microsoft.com/en-us/dotnet/api/system.text.regularexpressions?view=netframework-4.8
• https://docs.microsoft.com/en-us/dotnet/api/system.text.regularexpressions.regex?view=netframework-4.8
• https://docs.microsoft.com/en-us/dotnet/api/system.text.regularexpressions.capture?view=netframework-4.8
• https://docs.microsoft.com/en-us/dotnet/api/system.text.regularexpressions.capturecollection?view=netframework-4.8#methods
• https://docs.microsoft.com/en-us/dotnet/api/system.text.regularexpressions.group?view=netframework-4.8
• https://docs.microsoft.com/en-us/dotnet/api/system.text.regularexpressions.groupcollection?view=netframework-4.8
• https://docs.microsoft.com/en-us/dotnet/api/system.text.regularexpressions.match?view=netframework-4.8
• https://docs.microsoft.com/en-us/dotnet/api/system.text.regularexpressions.matchcollection?view=netframework-4.8