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11/18/2011

StringComparer Class

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Represents a string comparison operation that uses specific case and culture-based or ordinal comparison rules.

Inheritance Hierarchy

System.Object
System.StringComparer

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
<ComVisibleAttribute(True)> _
Public MustInherit Class StringComparer _
    Implements IComparer, IEqualityComparer, IComparer(Of String),  _
    IEqualityComparer(Of String)

[ComVisibleAttribute(true)]
public abstract class StringComparer : IComparer, 
    IEqualityComparer, IComparer<string>, IEqualityComparer<string>

The StringComparer type exposes the following members.

Constructors

	Name	Description
	StringComparer	Initializes a new instance of the StringComparer class.

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Properties

	Name	Description
	CurrentCulture	Gets a StringComparer object that performs a case-sensitive string comparison using the word comparison rules of the current culture.
	CurrentCultureIgnoreCase	Gets a StringComparer object that performs case-insensitive string comparisons using the word comparison rules of the current culture.
	InvariantCulture	Gets a StringComparer object that performs a case-sensitive string comparison using the word comparison rules of the invariant culture.
	InvariantCultureIgnoreCase	Gets a StringComparer object that performs a case-insensitive string comparison using the word comparison rules of the invariant culture.
	Ordinal	Gets a StringComparer object that performs a case-sensitive ordinal string comparison.
	OrdinalIgnoreCase	Gets a StringComparer object that performs a case-insensitive ordinal string comparison.

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Methods

	Name	Description
	Compare(Object, Object)	When overridden in a derived class, compares two objects and returns an indication of their relative sort order.
	Compare(String, String)	When overridden in a derived class, compares two strings and returns an indication of their relative sort order.
	Create	Creates a StringComparer object that compares strings according to the rules of a specified culture.
	Equals(Object)	Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
	Equals(Object, Object)	When overridden in a derived class, indicates whether two objects are equal.
	Equals(String, String)	When overridden in a derived class, indicates whether two strings are equal.
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode()	Serves as a hash function for a particular type. (Inherited from Object.)
	GetHashCode(Object)	When overridden in a derived class, gets the hash code for the specified object.
	GetHashCode(String)	When overridden in a derived class, gets the hash code for the specified string.
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	ToString	Returns a string that represents the current object. (Inherited from Object.)

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Remarks

An object derived from the StringComparer class embodies string-based comparison, equality, and hash code operations that take into account both case and culture-specific comparison rules. You can use the StringComparer class to create a type-specific comparison to sort the elements in a generic collection.

A comparison operation that is represented by the StringComparer class is defined to be either case-sensitive or case-insensitive, and use either word (culture-sensitive) or ordinal (culture-insensitive) comparison rules. For more information about word and ordinal comparison rules, see System.Globalization.CompareOptions.

Implemented Properties

You might be confused about how to use the StringComparer class properties because of a seeming contradiction. The StringComparer class is declared abstract (MustInherit in Visual Basic), which means its members can be invoked only on an object of a class derived from the StringComparer class. The contradiction is that each property of the StringComparer class is declared static (Shared in Visual Basic), which means the property can be invoked without first creating a derived class.

You can call a StringComparer property directly because each property actually returns an instance of an anonymous class that is derived from the StringComparer class. Consequently, the type of each property value is StringComparer, which is the base class of the anonymous class, not the type of the anonymous class itself. Each StringComparer class property returns a StringComparer object that supports predefined case and comparison rules.

Examples

The following code example demonstrates the properties and the Create method of the StringComparer class. The example illustrates how different StringComparer objects sort three versions of the Latin letter I.

' This code example demonstrates members of the System.StringComparer class.

Imports System.Collections
Imports System.Collections.Generic
Imports System.Globalization
Imports System.Threading

Class Example

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      ' Create a list of string.
      Dim list As New List(Of String)

      ' Get the tr-TR (Turkish-Turkey) culture.
      Dim turkish As New CultureInfo("tr-TR")

      ' Get the culture that is associated with the current thread.
      Dim thisCulture As CultureInfo = Thread.CurrentThread.CurrentCulture

      ' Get the standard StringComparers.
      Dim invCmp As StringComparer = StringComparer.InvariantCulture
      Dim invICCmp As StringComparer = StringComparer.InvariantCultureIgnoreCase
      Dim currCmp As StringComparer = StringComparer.CurrentCulture
      Dim currICCmp As StringComparer = StringComparer.CurrentCultureIgnoreCase
      Dim ordCmp As StringComparer = StringComparer.Ordinal
      Dim ordICCmp As StringComparer = StringComparer.OrdinalIgnoreCase

      ' Create a StringComparer that uses the Turkish culture and ignores case.
      Dim turkICComp As StringComparer = StringComparer.Create(turkish, True)

      ' Define three strings consisting of different versions of the letter I.
      ' LATIN CAPITAL LETTER I (U+0049)
      Dim capitalLetterI As String = "I"

      ' LATIN SMALL LETTER I (U+0069)
      Dim smallLetterI As String = "i"

      ' LATIN SMALL LETTER DOTLESS I (U+0131)
      Dim smallLetterDotlessI As String = "ı"

      ' Add the three strings to the list.
      list.Add(capitalLetterI)
      list.Add(smallLetterI)
      list.Add(smallLetterDotlessI)

      ' Display the original list order.
      Display(outputBlock, list, "The original order of the list entries...")

      ' Sort the list using the invariant culture.
      list.Sort(invCmp)
      Display(outputBlock, list, "Invariant culture...")
      list.Sort(invICCmp)
      Display(outputBlock, list, "Invariant culture, ignore case...")

      ' Sort the list using the current culture.
      outputBlock.Text += String.Format("The current culture is ""{0}"".", thisCulture.Name) & vbCrLf
      list.Sort(currCmp)
      Display(outputBlock, list, "Current culture...")
      list.Sort(currICCmp)
      Display(outputBlock, list, "Current culture, ignore case...")

      ' Sort the list using the ordinal value of the character code points.
      list.Sort(ordCmp)
      Display(outputBlock, list, "Ordinal...")
      list.Sort(ordICCmp)
      Display(outputBlock, list, "Ordinal, ignore case...")

      ' Sort the list using the Turkish culture, which treats LATIN SMALL LETTER 
      ' DOTLESS I differently than LATIN SMALL LETTER I.
      list.Sort(turkICComp)
      Display(outputBlock, list, "Turkish culture, ignore case...")

   End Sub 'Main

   Public Shared Sub Display(ByVal outputBlock As System.Windows.Controls.TextBlock, ByVal lst As List(Of String), ByVal title As String)
      Dim c As Char
      Dim s As String
      Dim codePoint As Integer

      outputBlock.Text &= title & vbCrLf
      For Each s In lst
         c = s(0)
         codePoint = Convert.ToInt32(c)
         outputBlock.Text += String.Format("0x{0:x}", codePoint) & vbCrLf
      Next s
      outputBlock.Text &= vbCrLf
   End Sub 'Display
End Class 'Sample '

'This code example produces the following results:
'
'The original order of the list entries...
'0x49
'0x69
'0x131
'
'Invariant culture...
'0x69
'0x49
'0x131
'
'Invariant culture, ignore case...
'0x49
'0x69
'0x131
'
'The current culture is "en-US".
'Current culture...
'0x69
'0x49
'0x131
'
'Current culture, ignore case...
'0x49
'0x69
'0x131
'
'Ordinal...
'0x49
'0x69
'0x131
'
'Ordinal, ignore case...
'0x69
'0x49
'0x131
'
'Turkish culture, ignore case...
'0x131
'0x49
'0x69
'

// This example demonstrates members of the 
// System.StringComparer class.

using System;
using System.Collections;
using System.Collections.Generic;
using System.Globalization;
using System.Threading;

class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      // Create a list of string.
      List<string> list = new List<string>();

      // Get the tr-TR (Turkish-Turkey) culture.
      CultureInfo turkish = new CultureInfo("tr-TR");

      // Get the culture that is associated with the current thread.
      CultureInfo thisCulture = Thread.CurrentThread.CurrentCulture;

      // Get the standard StringComparers.
      StringComparer invCmp = StringComparer.InvariantCulture;
      StringComparer invICCmp = StringComparer.InvariantCultureIgnoreCase;
      StringComparer currCmp = StringComparer.CurrentCulture;
      StringComparer currICCmp = StringComparer.CurrentCultureIgnoreCase;
      StringComparer ordCmp = StringComparer.Ordinal;
      StringComparer ordICCmp = StringComparer.OrdinalIgnoreCase;

      // Create a StringComparer that uses the Turkish culture and ignores case.
      StringComparer turkICComp = StringComparer.Create(turkish, true);

      // Define three strings consisting of different versions of the letter I.
      // LATIN CAPITAL LETTER I (U+0049)
      string capitalLetterI = "I";

      // LATIN SMALL LETTER I (U+0069)
      string smallLetterI = "i";

      // LATIN SMALL LETTER DOTLESS I (U+0131)
      string smallLetterDotlessI = "\u0131";

      // Add the three strings to the list.
      list.Add(capitalLetterI);
      list.Add(smallLetterI);
      list.Add(smallLetterDotlessI);

      // Display the original list order.
      Display(outputBlock, list, "The original order of the list entries...");

      // Sort the list using the invariant culture.
      list.Sort(invCmp);
      Display(outputBlock, list, "Invariant culture...");
      list.Sort(invICCmp);
      Display(outputBlock, list, "Invariant culture, ignore case...");

      // Sort the list using the current culture.
      outputBlock.Text += String.Format("The current culture is \"{0}\".", thisCulture.Name) + "\n";
      list.Sort(currCmp);
      Display(outputBlock, list, "Current culture...");
      list.Sort(currICCmp);
      Display(outputBlock, list, "Current culture, ignore case...");

      // Sort the list using the ordinal value of the character code points.
      list.Sort(ordCmp);
      Display(outputBlock, list, "Ordinal...");
      list.Sort(ordICCmp);
      Display(outputBlock, list, "Ordinal, ignore case...");

      // Sort the list using the Turkish culture, which treats LATIN SMALL LETTER 
      // DOTLESS I differently than LATIN SMALL LETTER I.
      list.Sort(turkICComp);
      Display(outputBlock, list, "Turkish culture, ignore case...");
   }

   public static void Display(System.Windows.Controls.TextBlock outputBlock, List<string> lst, string title)
   {
      Char c;
      int codePoint;
      outputBlock.Text += title + "\n";
      foreach (string s in lst)
      {
         c = s[0];
         codePoint = Convert.ToInt32(c);
         outputBlock.Text += String.Format("0x{0:x}", codePoint) + "\n";
      }
      outputBlock.Text += "\n";
   }
}
/*
This code example produces the following results:

The original order of the list entries...
0x49
0x69
0x131

Invariant culture...
0x69
0x49
0x131

Invariant culture, ignore case...
0x49
0x69
0x131

The current culture is "en-US".
Current culture...
0x69
0x49
0x131

Current culture, ignore case...
0x49
0x69
0x131

Ordinal...
0x49
0x69
0x131

Ordinal, ignore case...
0x69
0x49
0x131

Turkish culture, ignore case...
0x131
0x49
0x69

*/

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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