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NormalizationForm Enumeration

Defines the type of normalization to perform.

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

public enum class 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 namespace System;
using namespace System::Text;
void PrintNormalization( Encoding^ enc );
int main()

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

void PrintNormalization( Encoding^ enc )
   Console::Write( "{0,-30} ", enc );
   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


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

.NET Framework

Supported in: 3.5, 3.0, 2.0