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String.Normalize Method (NormalizationForm)

Returns a new string whose textual value is the same as this string, but whose binary representation is in the specified Unicode normalization form.

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

public string Normalize(
	NormalizationForm normalizationForm
)

Parameters

normalizationForm
Type: System.Text.NormalizationForm

A Unicode normalization form.

Return Value

Type: System.String
A new string whose textual value is the same as this string, but whose binary representation is in the normalization form specified by the normalizationForm parameter.

ExceptionCondition
ArgumentException

The current instance contains invalid Unicode characters.

Some Unicode characters have multiple equivalent binary representations consisting of sets of combining and/or composite Unicode characters. The existence of multiple representations for a single character complicates searching, sorting, matching, and other operations.

The Unicode standard defines a process called normalization that returns one binary representation when given any of the equivalent binary representations of a character. Normalization can be performed with several algorithms, called normalization forms, that obey different rules. The .NET Framework supports the four normalization forms (C, D, KC, and KD) that are defined by the Unicode standard. When two strings are represented in the same normalization form, they can be compared by using ordinal comparison.

To normalize and compare two strings, do the following:

  1. Obtain the strings to be compared from an input source, such as a file or a user input device.

  2. Call the Normalize(NormalizationForm) method to normalize the strings to a specified normalization form.

  3. To compare two strings, call a method that supports ordinal string comparison, such as the Compare(String, String, StringComparison) method, and supply a value of StringComparison.Ordinal or StringComparison.OrdinalIgnoreCase as the StringComparison argument. To sort an array of normalized strings, pass a comparer value of StringComparer.Ordinal or StringComparer.OrdinalIgnoreCase to an appropriate overload of Array.Sort.

  4. Emit the strings in the sorted output based on the order indicated by the previous step.

For a description of supported Unicode normalization forms, see System.Text.NormalizationForm.

Notes to Callers

The IsNormalized method returns false as soon as it encounters the first non-normalized character in a string. Therefore, if a string contains non-normalized characters followed by invalid Unicode characters, the Normalize method may throw an ArgumentException although IsNormalized returns false.

The following example normalizes a string to each of four normalization forms, confirms the string was normalized to the specified normalization form, then lists the code points in the normalized string.

using System;
using System.Text;

class Example
{
    public static void Main() 
    {
       // Character c; combining characters acute and cedilla; character 3/4 
       string s1 = new String( new char[] {'\u0063', '\u0301', '\u0327', '\u00BE'});
       string s2 = null;
       string divider = new String('-', 80);
       divider = String.Concat(Environment.NewLine, divider, Environment.NewLine);

       Show("s1", s1);
       Console.WriteLine();
       Console.WriteLine("U+0063 = LATIN SMALL LETTER C");
       Console.WriteLine("U+0301 = COMBINING ACUTE ACCENT");
       Console.WriteLine("U+0327 = COMBINING CEDILLA");
       Console.WriteLine("U+00BE = VULGAR FRACTION THREE QUARTERS");
       Console.WriteLine(divider);

       Console.WriteLine("A1) Is s1 normalized to the default form (Form C)?: {0}", 
                                    s1.IsNormalized());
       Console.WriteLine("A2) Is s1 normalized to Form C?:  {0}", 
                                    s1.IsNormalized(NormalizationForm.FormC));
       Console.WriteLine("A3) Is s1 normalized to Form D?:  {0}", 
                                    s1.IsNormalized(NormalizationForm.FormD));
       Console.WriteLine("A4) Is s1 normalized to Form KC?: {0}", 
                                    s1.IsNormalized(NormalizationForm.FormKC));
       Console.WriteLine("A5) Is s1 normalized to Form KD?: {0}", 
                                    s1.IsNormalized(NormalizationForm.FormKD));

       Console.WriteLine(divider);

       Console.WriteLine("Set string s2 to each normalized form of string s1.");
       Console.WriteLine();
       Console.WriteLine("U+1E09 = LATIN SMALL LETTER C WITH CEDILLA AND ACUTE");
       Console.WriteLine("U+0033 = DIGIT THREE");
       Console.WriteLine("U+2044 = FRACTION SLASH");
       Console.WriteLine("U+0034 = DIGIT FOUR");
       Console.WriteLine(divider);

       s2 = s1.Normalize();
       Console.Write("B1) Is s2 normalized to the default form (Form C)?: ");
       Console.WriteLine(s2.IsNormalized());
       Show("s2", s2);
       Console.WriteLine();

       s2 = s1.Normalize(NormalizationForm.FormC);
       Console.Write("B2) Is s2 normalized to Form C?: ");
       Console.WriteLine(s2.IsNormalized(NormalizationForm.FormC));
       Show("s2", s2);
       Console.WriteLine();

       s2 = s1.Normalize(NormalizationForm.FormD);
       Console.Write("B3) Is s2 normalized to Form D?: ");
       Console.WriteLine(s2.IsNormalized(NormalizationForm.FormD));
       Show("s2", s2);
       Console.WriteLine();

       s2 = s1.Normalize(NormalizationForm.FormKC);
       Console.Write("B4) Is s2 normalized to Form KC?: ");
       Console.WriteLine(s2.IsNormalized(NormalizationForm.FormKC));
       Show("s2", s2);
       Console.WriteLine();

       s2 = s1.Normalize(NormalizationForm.FormKD);
       Console.Write("B5) Is s2 normalized to Form KD?: ");
       Console.WriteLine(s2.IsNormalized(NormalizationForm.FormKD));
       Show("s2", s2);
       Console.WriteLine();
    }

    private static void Show(string title, string s)
    {
       Console.Write("Characters in string {0} = ", title);
       foreach(short x in s) {
           Console.Write("{0:X4} ", x);
       }
       Console.WriteLine();
    }
}
/*
This example produces the following results:

Characters in string s1 = 0063 0301 0327 00BE

U+0063 = LATIN SMALL LETTER C
U+0301 = COMBINING ACUTE ACCENT
U+0327 = COMBINING CEDILLA
U+00BE = VULGAR FRACTION THREE QUARTERS

--------------------------------------------------------------------------------

A1) Is s1 normalized to the default form (Form C)?: False
A2) Is s1 normalized to Form C?:  False
A3) Is s1 normalized to Form D?:  False
A4) Is s1 normalized to Form KC?: False
A5) Is s1 normalized to Form KD?: False

--------------------------------------------------------------------------------

Set string s2 to each normalized form of string s1.

U+1E09 = LATIN SMALL LETTER C WITH CEDILLA AND ACUTE
U+0033 = DIGIT THREE
U+2044 = FRACTION SLASH
U+0034 = DIGIT FOUR

--------------------------------------------------------------------------------

B1) Is s2 normalized to the default form (Form C)?: True
Characters in string s2 = 1E09 00BE

B2) Is s2 normalized to Form C?: True
Characters in string s2 = 1E09 00BE

B3) Is s2 normalized to Form D?: True
Characters in string s2 = 0063 0327 0301 00BE

B4) Is s2 normalized to Form KC?: True
Characters in string s2 = 1E09 0033 2044 0034

B5) Is s2 normalized to Form KD?: True
Characters in string s2 = 0063 0327 0301 0033 2044 0034

*/

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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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