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DecoderReplacementFallback Class

Provides a failure-handling mechanism, called a fallback, for an encoded input byte sequence that cannot be converted to an output character. The fallback emits a user-specified replacement string instead of a decoded input byte sequence. This class cannot be inherited.

System.Object
  System.Text.DecoderFallback
    System.Text.DecoderReplacementFallback

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

'Declaration
<SerializableAttribute> _
Public NotInheritable Class DecoderReplacementFallback _
	Inherits DecoderFallback

The DecoderReplacementFallback type exposes the following members.

  NameDescription
Public methodDecoderReplacementFallbackInitializes a new instance of the DecoderReplacementFallback class.
Public methodDecoderReplacementFallback(String)Initializes a new instance of the DecoderReplacementFallback class using a specified replacement string.
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  NameDescription
Public propertyDefaultStringGets the replacement string that is the value of the DecoderReplacementFallback object.
Public propertyMaxCharCountGets the number of characters in the replacement string for the DecoderReplacementFallback object. (Overrides DecoderFallback.MaxCharCount.)
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  NameDescription
Public methodCreateFallbackBufferCreates a DecoderFallbackBuffer object that is initialized with the replacement string of this DecoderReplacementFallback object. (Overrides DecoderFallback.CreateFallbackBuffer.)
Public methodEqualsIndicates whether the value of a specified object is equal to the DecoderReplacementFallback object. (Overrides Object.Equals(Object).)
Public methodGetHashCodeRetrieves the hash code for the value of the DecoderReplacementFallback object. (Overrides Object.GetHashCode.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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A common reason for an encoding or decoding operation to fail is if the underlying encoding class does not provide a mapping between a character and an equivalent byte sequence. If an input byte sequence cannot be converted to an output character, a DecoderReplacementFallback object emits a replacement string into the output to represent the original input byte sequence. The conversion process then continues to decode the remainder of the original input.

The value of a DecoderReplacementFallback object is the replacement string used to initialize that object.

The following code example demonstrates the DecoderReplacementFallback class.

' This example demonstrates the DecoderReplacementFallback class. 
Imports System
Imports System.Text

Class Sample
    Public Shared Sub Main() 

        ' Create an encoding, which is equivalent to calling the  
        ' ASCIIEncoding class constructor.  
        ' The DecoderReplacementFallback parameter specifies that the  
        ' string "(error)" is to replace characters that cannot be decoded.  
        ' An encoder replacement fallback is also specified, but in this code 
        ' example the encoding operation cannot fail.   

        Dim erf As New EncoderReplacementFallback("(unknown)")
        Dim drf As New DecoderReplacementFallback("(error)")
        Dim ae As Encoding = Encoding.GetEncoding("us-ascii", erf, drf)
        Dim inputString As String = "XYZ" 
        Dim decodedString As String 
        Dim twoNewLines As String = vbCrLf & vbCrLf
        Dim numberOfEncodedBytes As Integer = ae.GetByteCount(inputString)
        ' Counteract the compiler implicitly adding an extra element. 
        Dim encodedBytes(numberOfEncodedBytes - 1) As Byte 

        ' --------------------------------------------------------------------------
        Console.Clear()

        ' Display the name of the encoding.
        Console.WriteLine("The name of the encoding is ""{0}""." & vbCrLf, ae.WebName)

        ' Display the input string in text.
        Console.WriteLine("Input string ({0} characters): ""{1}""", _
                          inputString.Length, inputString)

        ' Display the input string in hexadecimal.  
        ' Each element is converted to an integer with Convert.ToInt32.
        Console.Write("Input string in hexadecimal: ")
        Dim c As Char 
        For Each c In  inputString.ToCharArray()
            Console.Write("0x{0:X2} ", Convert.ToInt32(c))
        Next c
        Console.Write(twoNewLines)

        ' -------------------------------------------------------------------------- 
        ' Encode the input string. 
        Console.WriteLine("Encode the input string...")
        numberOfEncodedBytes = ae.GetBytes(inputString, 0, inputString.Length, _
                                           encodedBytes, 0)

        ' Display the encoded bytes.  
        ' Each element is converted to an integer with Convert.ToInt32.
        Console.WriteLine("Encoded bytes in hexadecimal ({0} bytes):" & vbCrLf, _
                                                         numberOfEncodedBytes)
        Dim b As Byte 
        For Each b In  encodedBytes
            Console.Write("0x{0:X2} ", Convert.ToInt32(b))
        Next b
        Console.Write(twoNewLines)

        ' -------------------------------------------------------------------------- 
        ' Replace the encoded byte sequences for the characters 'X' and 'Z' with the  
        ' value 0xFF, which is outside the valid range of 0x00 to 0x7F for  
        ' ASCIIEncoding. The resulting byte sequence is actually the beginning of  
        ' this code example because it is the input to the decoder operation, and  
        ' is equivalent to a corrupted or improperly encoded byte sequence. 

        encodedBytes(0) = &HFF
        encodedBytes(2) = &HFF

        Console.WriteLine("Display the corrupted byte sequence...")
        Console.WriteLine("Encoded bytes in hexadecimal ({0} bytes):" & vbCrLf, _
                           numberOfEncodedBytes)
        For Each b In  encodedBytes
            Console.Write("0x{0:X2} ", Convert.ToInt32(b))
        Next b
        Console.Write(twoNewLines)

        ' -------------------------------------------------------------------------- 
        ' Decode the encoded bytes.
        Console.WriteLine("Compare the decoded bytes to the input string...")
        decodedString = ae.GetString(encodedBytes)

        ' Display the input string and the decoded string for comparison.
        Console.WriteLine("Input string:  ""{0}""", inputString)
        Console.WriteLine("Decoded string:""{0}""", decodedString)

    End Sub 'Main
End Class 'Sample

'This code example produces the following results: 

'The name of the encoding is "us-ascii". 

'Input string (3 characters): "XYZ" 
'Input string in hexadecimal: 0x58 0x59 0x5A 

'Encode the input string... 
'Encoded bytes in hexadecimal (3 bytes): 

'0x58 0x59 0x5A 

'Display the corrupted byte sequence... 
'Encoded bytes in hexadecimal (3 bytes): 

'0xFF 0x59 0xFF 

'Compare the decoded bytes to the input string... 
'Input string:  "XYZ" 
'Decoded string:"(error)Y(error)" 
'

.NET Framework

Supported in: 4.5.2, 4.5.1, 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.

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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