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Encoding.UTF8 Property

Updated: October 2010

Gets an encoding for the UTF-8 format.

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

'Declaration
Public Shared ReadOnly Property UTF8 As Encoding
'Usage
Dim value As Encoding 

value = Encoding.UTF8

Property Value

Type: System.Text.Encoding
An encoding for the UTF-8 format.

This property returns a UTF8Encoding object that encodes Unicode characters into a sequence of one to four bytes per character, and that decodes a UTF-8-encoded byte array to Unicode characters. For information about the character encodings supported by the .NET Framework and a discussion of which Unicode encoding to use, see Understanding Encodings.

The UTF8Encoding object that is returned by this property may not have the appropriate behavior for your application. It uses replacement fallback to replace each string that it cannot encode and each byte that it cannot decode with a question mark ("?") character. Instead, you can call the UTF8Encoding.UTF8Encoding(Boolean, Boolean) constructor to instantiate a UTF8Encoding object whose fallback is either an EncoderFallbackException or a DecoderFallbackException, as the following example illustrates.

Imports System.Text

Module Example
   Public Sub Main()
      Dim enc As Encoding = New UTF8Encoding(True, True)
      Dim value As String = String.Format("{0} {1}{2} {3}", _
                            ChrW(&h00C4), ChrW(&hD802), ChrW(&h0033), ChrW(&h00AE))

      Try 
         Dim bytes() As Byte = enc.GetBytes(value)
         For Each byt As Byte In bytes
            Console.Write("{0:X2} ", byt)
         Next       
         Console.WriteLine()
         Dim value2 As String = enc.GetString(bytes)
         Console.WriteLine(value2)
      Catch e As EncoderFallbackException
         Console.WriteLine("Unable to encode {0} at index {1}", _
                           If(e.IsUnknownSurrogate(), _
                              String.Format("U+{0:X4} U+{1:X4}", _ 
                                            Convert.ToUInt16(e.CharUnknownHigh), _
                                            Convert.ToUInt16(e.CharUnknownLow)), _
                              String.Format("U+{0:X4}", _ 
                                            Convert.ToUInt16(e.CharUnknown))), _
                           e.Index)
      End Try 
   End Sub 
End Module 
' The example displays the following output: 
'       Unable to encode U+D802 at index 2

The following example determines the number of bytes required to encode a character array, encodes the characters, and displays the resulting bytes.

Imports System
Imports System.Text
Imports Microsoft.VisualBasic

Public Class SamplesEncoding   

   Public Shared Sub Main()

      ' The characters to encode: 
      '    Latin Small Letter Z (U+007A) 
      '    Latin Small Letter A (U+0061) 
      '    Combining Breve (U+0306) 
      '    Latin Small Letter AE With Acute (U+01FD) 
      '    Greek Small Letter Beta (U+03B2) 
      '    a high-surrogate value (U+D8FF) 
      '    a low-surrogate value (U+DCFF) 
      Dim myChars() As Char = {"z"c, "a"c, ChrW(&H0306), ChrW(&H01FD), ChrW(&H03B2), ChrW(&HD8FF), ChrW(&HDCFF)}


      ' Get different encodings. 
      Dim u7 As Encoding = Encoding.UTF7
      Dim u8 As Encoding = Encoding.UTF8
      Dim u16LE As Encoding = Encoding.Unicode
      Dim u16BE As Encoding = Encoding.BigEndianUnicode
      Dim u32 As Encoding = Encoding.UTF32

      ' Encode the entire array, and print out the counts and the resulting bytes.
      PrintCountsAndBytes(myChars, u7)
      PrintCountsAndBytes(myChars, u8)
      PrintCountsAndBytes(myChars, u16LE)
      PrintCountsAndBytes(myChars, u16BE)
      PrintCountsAndBytes(myChars, u32)

   End Sub 'Main


   Public Shared Sub PrintCountsAndBytes(chars() As Char, enc As Encoding)

      ' Display the name of the encoding used.
      Console.Write("{0,-30} :", enc.ToString())

      ' Display the exact byte count. 
      Dim iBC As Integer = enc.GetByteCount(chars)
      Console.Write(" {0,-3}", iBC)

      ' Display the maximum byte count. 
      Dim iMBC As Integer = enc.GetMaxByteCount(chars.Length)
      Console.Write(" {0,-3} :", iMBC)

      ' Encode the array of chars. 
      Dim bytes As Byte() = enc.GetBytes(chars)

      ' Display all the encoded bytes.
      PrintHexBytes(bytes)

   End Sub 'PrintCountsAndBytes


   Public Shared Sub PrintHexBytes(bytes() As Byte)

      If bytes Is Nothing OrElse bytes.Length = 0 Then
         Console.WriteLine("<none>")
      Else 
         Dim i As Integer 
         For i = 0 To bytes.Length - 1
            Console.Write("{0:X2} ", bytes(i))
         Next i
         Console.WriteLine()
      End If 

   End Sub 'PrintHexBytes 

End Class 'SamplesEncoding


'This code produces the following output. 

'System.Text.UTF7Encoding       : 18  23  :7A 61 2B 41 77 59 42 2F 51 4F 79 32 50 2F 63 2F 77 2D 
'System.Text.UTF8Encoding       : 12  24  :7A 61 CC 86 C7 BD CE B2 F1 8F B3 BF 
'System.Text.UnicodeEncoding    : 14  16  :7A 00 61 00 06 03 FD 01 B2 03 FF D8 FF DC 
'System.Text.UnicodeEncoding    : 14  16  :00 7A 00 61 03 06 01 FD 03 B2 D8 FF DC FF 
'System.Text.UTF32Encoding      : 24  32  :7A 00 00 00 61 00 00 00 06 03 00 00 FD 01 00 00 B2 03 00 00 FF FC 04 00

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

Date

History

Reason

October 2010

Noted replacement fallback behavior.

Customer feedback.

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