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Regex.GroupNumberFromName Method

Returns the group number that corresponds to the specified group name.

Namespace:  System.Text.RegularExpressions
Assembly:  System (in System.dll)

public int GroupNumberFromName(
	string name


Type: System.String
The group name to convert to the corresponding group number.

Return Value

Type: System.Int32
The group number that corresponds to the specified group name, or -1 if name is not a valid group name.


name is null.

A regular expression pattern may contain either named or numbered capturing groups, which delineate subexpressions within a pattern match. Numbered groups are delimited by the syntax (subexpression) and are assigned numbers based on their order in the regular expression. Named groups are delimited by the syntax (?<name>subexpression) or (?'name'subexpression), where name is the name by which the subexpression will be identified. (For more information, see Grouping Constructs.) The GroupNumberFromName method identifies both named groups and numbered groups by their ordinal positions in the regular expression. Ordinal position zero always represents the entire regular expression. All numbered groups are then counted before named groups, regardless of their actual position in the regular expression pattern.

If name is the string representation of a group number that is present in the regular expression pattern, the method returns that number. If name corresponds to a named capturing group that is present in the regular expression pattern, the method returns its corresponding number. The comparison of name with the group name is case-sensitive. If name does not correspond to the name of a capturing group or to the string representation of the number of a capturing group, the method returns -1.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: 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

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.