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NormalizationForm Enumeration

Defines the type of normalization to perform.

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

public enum NormalizationForm

Member nameDescription
FormCIndicates that a Unicode string is normalized using full canonical decomposition, followed by the replacement of sequences with their primary composites, if possible.
FormDIndicates that a Unicode string is normalized using full canonical decomposition.
FormKCIndicates that a Unicode string is normalized using full compatibility decomposition, followed by the replacement of sequences with their primary composites, if possible.
FormKDIndicates that a Unicode string is normalized using full compatibility decomposition.

Some Unicode sequences are considered equivalent because they represent the same character. For example, the following are considered equivalent because any of these can be used to represent "ắ":

  • "\u1EAF"

  • "\u0103\u0301"

  • "\u0061\u0306\u0301"

However, ordinal, that is, binary, comparisons consider these sequences different because they contain different Unicode code values. Before performing ordinal comparisons, applications must normalize these strings to decompose them into their basic components.

Each composite Unicode character is mapped to a more basic sequence of one or more characters. The process of decomposition replaces composite characters in a string with their more basic mappings. A full decomposition recursively performs this replacement until none of the characters in the string can be decomposed further.

Unicode defines two types of decompositions: compatibility decomposition and canonical decomposition. In compatibility decomposition, formatting information might be lost. In canonical decomposition, which is a subset of compatibility decomposition, formatting information is preserved.

Two sets of characters are considered to have canonical equivalence if their full canonical decompositions are identical. Likewise, two sets of characters are considered to have compatibility equivalence if their full compatibility decompositions are identical.

For more information on normalization, decompositions and equivalence, see The Unicode Standard at the Unicode home page.

The following code example determines if an encoding is always normalized using the different normalization forms.

using System;
using System.Text;

public class SamplesASCIIEncoding  {

   public static void Main()  {

      // Display the value of IsAlwaysNormalized for every normalization form.
      Console.WriteLine( "{0,30} FormC   FormKC  FormD   FormKD", "" );
      PrintNormalization( new UTF32Encoding( true, true, true ) );
      PrintNormalization( new UnicodeEncoding( true, true, true ) );
      PrintNormalization( new UTF8Encoding( true, true ) );
      PrintNormalization( new UTF7Encoding( true ) );
      PrintNormalization( new ASCIIEncoding() );


   public static void PrintNormalization( Encoding enc )  {
      Console.Write( "{0,-30} ", enc.ToString() );
      Console.Write( "{0,-8}", enc.IsAlwaysNormalized( NormalizationForm.FormC ) );
      Console.Write( "{0,-8}", enc.IsAlwaysNormalized( NormalizationForm.FormKC ) );
      Console.Write( "{0,-8}", enc.IsAlwaysNormalized( NormalizationForm.FormD ) );
      Console.WriteLine( "{0,-8}", enc.IsAlwaysNormalized( NormalizationForm.FormKD ) );


This code produces the following output.

                               FormC   FormKC  FormD   FormKD
System.Text.UTF32Encoding      False   False   False   False
System.Text.UnicodeEncoding    False   False   False   False
System.Text.UTF8Encoding       False   False   False   False
System.Text.UTF7Encoding       False   False   False   False
System.Text.ASCIIEncoding      True    True    True    True


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

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.
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