IdnMapping Class

Supports the use of non-ASCII characters for Internet domain names. This class cannot be inherited.

System.Object
  System.Globalization.IdnMapping

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

public sealed class IdnMapping

The IdnMapping type exposes the following members.

  NameDescription
Public methodIdnMappingInitializes a new instance of the IdnMapping class.
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  NameDescription
Public propertyAllowUnassignedGets or sets a value indicating whether unassigned Unicode code points are used in operations performed by members of the current IdnMapping object.
Public propertyUseStd3AsciiRulesGets or sets a value indicating whether standard or nonstandard naming conventions are used in operations performed by members of the current IdnMapping object.
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  NameDescription
Public methodEqualsIndicates whether a specified object and this IdnMapping object are equal. (Overrides Object.Equals(Object).)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetAscii(String)Encodes a string of one or more domain name labels that consist of Unicode characters to a string of Unicode characters in the US-ASCII character range.
Public methodGetAscii(String, Int32)Encodes a substring of one or more domain name labels that consist of Unicode characters to a string of Unicode characters in the US-ASCII character range.
Public methodGetAscii(String, Int32, Int32)Encodes a substring of one or more domain name labels that consist of Unicode characters to a string of Unicode characters in the US-ASCII character range. The string is formatted according to the Internationalizing Domain Names in Applications (IDNA) standard.
Public methodGetHashCodeReturns a hash code for this IdnMapping object. (Overrides Object.GetHashCode().)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodGetUnicode(String)Decodes a string of one or more domain name labels encoded according to the Internationalizing Domain Names in Applications (IDNA) standard to a string of Unicode characters.
Public methodGetUnicode(String, Int32)Decodes a substring of one or more domain name labels encoded according to the Internationalizing Domain Names in Applications (IDNA) standard to a string of Unicode characters.
Public methodGetUnicode(String, Int32, Int32)Decodes a substring of one or more domain name labels encoded according to the Internationalizing Domain Names in Applications (IDNA) standard to a string of Unicode characters.
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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An Internet domain name consists of one or more parts, called domain name labels, separated by label separators. For example, the domain name "www.microsoft.com" consists of the labels, "www", "microsoft", and "com" separated by periods.

The Internationalizing Domain Names in Applications (IDNA) mechanism maps an internationalized domain name that contains Unicode characters outside the US-ASCII character range to an IDNA domain name that consists of Unicode characters solely in the displayable US-ASCII character range. The IDNA mechanism is used to convert only domain names, not data transmitted over the Internet.

The IdnMapping class embodies and extends the IDNA mechanism. The GetAscii method normalizes a domain name, converts the normalized name to a representation that consists of displayable Unicode characters in the US-ASCII code point range (U+0020 to U+007E), and prepends an ASCII Compatible Encoding prefix ("xn--") to each label.

The label separator characters IDEOGRAPHIC FULL STOP (U+3002), FULLWIDTH FULL STOP (U+FF0E), and HALFWIDTH IDEOGRAPHIC FULL STOP (U+FF61) are converted to the label separator FULL STOP (period, U+002E).

For more information, see the RFC 3490 standard, "Internationalizing Domain Names in Applications," at Request for Comments (RFC). Standards bodies are working on updates to the IDNA standard; see the Internet Engineering Task Force working group (http://tools.ietf.org/wg/idnabis/). There will probably eventually be a follow up to the current IDN standards.

The following code example uses the GetAscii(String, Int32, Int32) method to convert a domain name to a domain name that complies with the IDNA standard. The GetUnicode(String, Int32, Int32) method then converts the standardized domain name back into the original domain name, except that the original label separators are replaced with the standard label separator.


// This example demonstrates the GetAscii and GetUnicode methods.
// For sake of illustration, this example uses the most complex
// form of those methods, not the most convenient.

using System;
using System.Globalization;

class Sample 
{
    public static void Main() 
    {
/* 
   Define a domain name consisting of the labels: GREEK SMALL LETTER 
   PI (U+03C0); IDEOGRAPHIC FULL STOP (U+3002); GREEK SMALL LETTER 
   THETA (U+03B8); FULLWIDTH FULL STOP (U+FF0E); and "com".
*/
    string name = "\u03C0\u3002\u03B8\uFF0Ecom";
    string international;
    string nonInternational;

    string msg1 = "the original non-internationalized \ndomain name:";
    string msg2 = "Allow unassigned characters?:     {0}";
    string msg3 = "Use non-internationalized rules?: {0}";
    string msg4 = "Convert the non-internationalized domain name to international format...";
    string msg5 = "Display the encoded domain name:\n\"{0}\"";
    string msg6 = "the encoded domain name:";
    string msg7 = "Convert the internationalized domain name to non-international format...";
    string msg8 = "the reconstituted non-internationalized \ndomain name:";
    string msg9 = "Visually compare the code points of the reconstituted string to the " +
                  "original.\n" +
                  "Note that the reconstituted string contains standard label " +
                  "separators (U+002e).";
// ----------------------------------------------------------------------------
    Console.Clear();
    CodePoints(name, msg1);
// ----------------------------------------------------------------------------

    IdnMapping idn = new IdnMapping();

    Console.WriteLine(msg2, idn.AllowUnassigned);
    Console.WriteLine(msg3, idn.UseStd3AsciiRules);
    Console.WriteLine();
// ----------------------------------------------------------------------------
    Console.WriteLine(msg4);
    international = idn.GetAscii(name, 0, name.Length);
    Console.WriteLine(msg5, international);
    Console.WriteLine();
    CodePoints(international, msg6);
// ----------------------------------------------------------------------------
    Console.WriteLine(msg7);
    nonInternational = idn.GetUnicode(international, 0, international.Length);
    CodePoints(nonInternational, msg8);
    Console.WriteLine(msg9);
    }
// ----------------------------------------------------------------------------
    static void CodePoints(string value, string title)
    {
    Console.WriteLine("Display the Unicode code points of {0}", title);
    foreach (char c in value) 
        {
        Console.Write("{0:x4} ", Convert.ToInt32(c));
        }
        Console.WriteLine();
        Console.WriteLine();
    }
}
/*
This code example produces the following results:

Display the Unicode code points of the original non-internationalized
domain name:
03c0 3002 03b8 ff0e 0063 006f 006d

Allow unassigned characters?:     False
Use non-internationalized rules?: False

Convert the non-internationalized domain name to international format...
Display the encoded domain name:
"xn--1xa.xn--txa.com"

Display the Unicode code points of the encoded domain name:
0078 006e 002d 002d 0031 0078 0061 002e 0078 006e 002d 002d 0074 0078 0061 002e 0063 006f
006d

Convert the internationalized domain name to non-international format...
Display the Unicode code points of the reconstituted non-internationalized
domain name:
03c0 002e 03b8 002e 0063 006f 006d

Visually compare the code points of the reconstituted string to the original.
Note that the reconstituted string contains standard label separators (U+002e).

*/


.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.

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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