IdnMapping.GetAscii Method (String, Int32)


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Encodes a substring of domain name labels that include Unicode characters outside the US-ASCII character range. The substring is converted to a string of displayable Unicode characters in the US-ASCII character range and is formatted according to the IDNA standard.

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

member GetAscii : 
        unicode:string *
        index:int -> string


Type: System.String

The string to convert, which consists of one or more domain name labels delimited with label separators.

Type: System.Int32

A zero-based offset into unicode that specifies the start of the substring to convert. The conversion operation continues to the end of the unicode string.

Return Value

Type: System.String

The equivalent of the substring specified by the unicode and index parameters, consisting of displayable Unicode characters in the US-ASCII character range (U+0020 to U+007E) and formatted according to the IDNA standard.

Exception Condition

unicode is null.


index is less than zero.


index is greater than the length of unicode.


unicode is invalid based on the AllowUnassigned and UseStd3AsciiRules properties, and the IDNA standard.

The unicode and index parameters define a substring with one or more labels that consist of valid Unicode characters. The labels are separated by label separators. The first character of the substring cannot begin with a label separator, but it can include and optionally end with a separator. The label separators are FULL STOP (period, U+002E), IDEOGRAPHIC FULL STOP (U+3002), FULLWIDTH FULL STOP (U+FF0E), and HALFWIDTH IDEOGRAPHIC FULL STOP (U+FF61). For example, the domain name "" consists of the labels, "www", "adatum", and "com", separated by periods.

A label cannot contain any of the following characters:

The GetAscii method converts all label separators to FULL STOP (period, U+002E).

If unicode contains no characters outside the US-ASCII character range and no characters within the US-ASCII character range are prohibited, the method returns unicode unchanged.

Notes to Callers:

In the .NET Framework 4.5, the IdnMapping class supports different versions of the IDNA standard, depending on the operating system in use:

See Unicode Technical Standard #46: IDNA Compatibility Processing for the differences in the way these standards handle particular sets of characters.

The following example removes the local part and the @ character from an email address, and passes the resulting domain name to the GetAscii(String, Int32) method to create a Punycode domain name, which is an encoded equivalent that consists of characters in the US-ASCII character range. The GetUnicode(String, Int32, Int32) method then converts the Punycode domain name back into the original domain name, but replaces the original label separators with the standard label separator.

No code example is currently available or this language may not be supported.

Universal Windows Platform
Available since 10
.NET Framework
Available since 2.0
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