DecoderExceptionFallback DecoderExceptionFallback DecoderExceptionFallback DecoderExceptionFallback Class

Definição

Fornece um mecanismo de tratamento de falha chamado fallback para uma sequência de bytes codificados de entrada que não pode ser convertida em um caractere de entrada.Provides a failure-handling mechanism, called a fallback, for an encoded input byte sequence that cannot be converted to an input character. O fallback gera uma exceção, em vez de decodificar a sequência de bytes de entrada.The fallback throws an exception instead of decoding the input byte sequence. Essa classe não pode ser herdada.This class cannot be inherited.

public ref class DecoderExceptionFallback sealed : System::Text::DecoderFallback
[System.Serializable]
public sealed class DecoderExceptionFallback : System.Text.DecoderFallback
type DecoderExceptionFallback = class
    inherit DecoderFallback
Public NotInheritable Class DecoderExceptionFallback
Inherits DecoderFallback
Herança
DecoderExceptionFallbackDecoderExceptionFallbackDecoderExceptionFallbackDecoderExceptionFallback
Atributos

Exemplos

O exemplo de código a seguir DecoderExceptionFallback demonstra DecoderFallbackException as classes e.The following code example demonstrates the DecoderExceptionFallback and DecoderFallbackException classes.

// This example demonstrates the DecoderExceptionFallback class.

using namespace System;
using namespace System::Text;

int main()
{
    // Create an encoding, which is equivalent to calling the
    // ASCIIEncoding class constructor.
    // The DecoderExceptionFallback parameter specifies that an exception
    // is thrown if a character cannot be encoded.
    // An encoder exception fallback is also specified, but in this code
    // example the encoding operation cannot fail.

    Encoding^ asciiEncoding = Encoding::GetEncoding("us-ascii",
        gcnew EncoderExceptionFallback(), gcnew DecoderExceptionFallback());
    String^ inputString = "XYZ";
    String^ decodedString;
    String^ twoNewLines = Environment::NewLine + Environment::NewLine ;

    array<Byte>^ encodedBytes = 
        gcnew array<Byte>(asciiEncoding->GetByteCount(inputString));
    int numberOfEncodedBytes = 0;

    // ---------------------------------------------------------------------
    Console::Clear();

    // Display the name of the encoding.
    Console::WriteLine("The name of the encoding is \"{0}\".{1}",
        asciiEncoding->WebName, Environment::NewLine);

    // Display the input string in text.
    Console::WriteLine("Input string ({0} characters): \"{1}\"",
        inputString->Length, inputString);

    // Display the input string in hexadecimal.
    Console::Write("Input string in hexadecimal: ");
    for each (char c in inputString)
    {
        Console::Write("0x{0:X2} ", c);
    }
    Console::Write(twoNewLines);

    // ---------------------------------------------------------------------
    // Encode the input string.

    Console::WriteLine("Encode the input string...");

    numberOfEncodedBytes = asciiEncoding->GetBytes(inputString, 0,
        inputString->Length, encodedBytes, 0);

    // Display the encoded bytes.
    Console::WriteLine("Encoded bytes in hexadecimal ({0} bytes):{1}",
        numberOfEncodedBytes, Environment::NewLine);
    for each (Byte b in encodedBytes)
    {
        Console::Write("0x{0:X2} ", 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] = 0xFF;
    encodedBytes[2] = 0xFF;

    Console::WriteLine("Display the corrupted byte sequence...");
    Console::WriteLine("Encoded bytes in hexadecimal ({0} bytes):{1}",
        numberOfEncodedBytes, Environment::NewLine);
    for each (Byte b in encodedBytes)
    {
        Console::Write("0x{0:X2} ", b);
    }
    Console::Write(twoNewLines);

    // ---------------------------------------------------------------------
    // Attempt to decode the encoded bytes. However, an exception is thrown
    // before the byte sequence can be decoded.

    Console::WriteLine("Compare the decoded bytes to the input string...");

    try
    {
        decodedString = asciiEncoding->GetString(encodedBytes);
        // This statement is never executed.
        Console::WriteLine("This statement is never executed.");
    }
    catch (DecoderFallbackException^ ex)
    {
        Console::WriteLine(ex);
        Console::WriteLine(
            "{0}*** THE CODE EXAMPLE TERMINATES HERE AS INTENDED. ***", 
            Environment::NewLine);
    }
}


/*
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...
System.Text.DecoderFallbackException: Unable to translate bytes [FF] at index 0 from speci
fied code page to Unicode.
at System.Text.DecoderExceptionFallbackBuffer.Throw(Byte[] bytesUnknown, Int32 index)
at System.Text.DecoderExceptionFallbackBuffer.Fallback(Byte[] bytesUnknown, Int32 index
)
at System.Text.DecoderFallbackBuffer.InternalFallback(Byte[] bytes, Byte* pBytes)
at System.Text.ASCIIEncoding.GetCharCount(Byte* bytes, Int32 count, DecoderNLS decoder)

at System.String.CreateStringFromEncoding(Byte* bytes, Int32 byteLength, Encoding encod
ing)
at System.Text.ASCIIEncoding.GetString(Byte[] bytes, Int32 byteIndex, Int32 byteCount)
at System.Text.Encoding.GetString(Byte[] bytes)
at Sample.Main()

*** THE CODE EXAMPLE TERMINATES HERE AS INTENDED. ***

*/
// This example demonstrates the DecoderExceptionFallback class.

using System;
using System.Text;

class Sample 
{
    public static void Main() 
    {

// Create an encoding, which is equivalent to calling the 
// ASCIIEncoding class constructor. 
// The DecoderExceptionFallback parameter specifies that an exception
// is thrown if a character cannot be encoded. 
// An encoder exception fallback is also specified, but in this code
// example the encoding operation cannot fail.  

    Encoding ae = Encoding.GetEncoding(
                  "us-ascii",
                  new EncoderExceptionFallback(), 
                  new DecoderExceptionFallback());
    string inputString = "XYZ";
    string decodedString;
    string twoNewLines = "\n\n";
    byte[] encodedBytes = new byte[ae.GetByteCount(inputString)];
    int numberOfEncodedBytes = 0;

// --------------------------------------------------------------------------
    Console.Clear();

// Display the name of the encoding.
    Console.WriteLine("The name of the encoding is \"{0}\".\n", ae.WebName);

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

// Display the input string in hexadecimal.
    Console.Write("Input string in hexadecimal: ");
    foreach (char c in inputString.ToCharArray()) 
        {
        Console.Write("0x{0:X2} ", (int)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.
    Console.WriteLine("Encoded bytes in hexadecimal ({0} bytes):\n", 
                       numberOfEncodedBytes);
    foreach (byte b in encodedBytes)
        {
        Console.Write("0x{0:X2} ", (int)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] = 0xFF;
    encodedBytes[2] = 0xFF;

    Console.WriteLine("Display the corrupted byte sequence...");
    Console.WriteLine("Encoded bytes in hexadecimal ({0} bytes):\n", 
                       numberOfEncodedBytes);
    foreach (byte b in encodedBytes)
        {
        Console.Write("0x{0:X2} ", (int)b);
        }
    Console.Write(twoNewLines);

// --------------------------------------------------------------------------
// Attempt to decode the encoded bytes. However, an exception is thrown 
// before the byte sequence can be decoded.

    Console.WriteLine("Compare the decoded bytes to the input string...");

    try {
        decodedString = ae.GetString(encodedBytes);
        }
    catch (DecoderFallbackException dfe)
        {
        Console.WriteLine(dfe);
        Console.WriteLine("\n*** THE CODE EXAMPLE TERMINATES HERE AS INTENDED. ***");
        return;
        }

// This statement is never executed.
    Console.WriteLine("This statement is never executed.");
    }
}
/*
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...
System.Text.DecoderFallbackException: Unable to translate bytes [FF] at index 0 from speci
fied code page to Unicode.
   at System.Text.DecoderExceptionFallbackBuffer.Throw(Byte[] bytesUnknown, Int32 index)
   at System.Text.DecoderExceptionFallbackBuffer.Fallback(Byte[] bytesUnknown, Int32 index
)
   at System.Text.DecoderFallbackBuffer.InternalFallback(Byte[] bytes, Byte* pBytes)
   at System.Text.ASCIIEncoding.GetCharCount(Byte* bytes, Int32 count, DecoderNLS decoder)

   at System.String.CreateStringFromEncoding(Byte* bytes, Int32 byteLength, Encoding encod
ing)
   at System.Text.ASCIIEncoding.GetString(Byte[] bytes, Int32 byteIndex, Int32 byteCount)
   at System.Text.Encoding.GetString(Byte[] bytes)
   at Sample.Main()

*** THE CODE EXAMPLE TERMINATES HERE AS INTENDED. ***

*/
' This example demonstrates the DecoderExceptionFallback class.
Imports System.Text

Class Sample
    Public Shared Sub Main() 
        
        ' Create an encoding, which is equivalent to calling the 
        ' ASCIIEncoding class constructor. 
        ' The DecoderExceptionFallback parameter specifies that an exception
        ' is thrown if a character cannot be encoded. 
        ' An encoder exception fallback is also specified, but in this code
        ' example the encoding operation cannot fail.  


        Dim eef As New EncoderExceptionFallback()
        Dim def As New DecoderExceptionFallback()
        Dim ae As Encoding = Encoding.GetEncoding("us-ascii", eef, def)
        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 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...")
        ' Each element is converted to an integer with Convert.ToInt32.
        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)
        
        ' --------------------------------------------------------------------------
        ' Attempt to decode the encoded bytes. However, an exception is thrown 
        ' before the byte sequence can be decoded.
        Console.WriteLine("Compare the decoded bytes to the input string...")
        
        Try
            decodedString = ae.GetString(encodedBytes)
        Catch dfe As DecoderFallbackException
            Console.WriteLine(dfe)
            Console.WriteLine(vbCrLf & _
                              "*** THE CODE EXAMPLE TERMINATES HERE AS INTENDED. ***")
            Return
        End Try
        
        ' This statement is never executed.
        Console.WriteLine("This statement is never executed.")
    
    End Sub
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...
'System.Text.DecoderFallbackException: Unable to translate bytes [FF] at index 0 from speci
'fied code page to Unicode.
'   at System.Text.DecoderExceptionFallbackBuffer.Throw(Byte[] bytesUnknown, Int32 index)
'   at System.Text.DecoderExceptionFallbackBuffer.Fallback(Byte[] bytesUnknown, Int32 index
')
'   at System.Text.DecoderFallbackBuffer.InternalFallback(Byte[] bytes, Byte* pBytes)
'   at System.Text.ASCIIEncoding.GetCharCount(Byte* bytes, Int32 count, DecoderNLS decoder)
'
'   at System.String.CreateStringFromEncoding(Byte* bytes, Int32 byteLength, Encoding encod
'ing)
'   at System.Text.ASCIIEncoding.GetString(Byte[] bytes, Int32 byteIndex, Int32 byteCount)
'   at System.Text.Encoding.GetString(Byte[] bytes)
'   at Sample.Main()
'
'*** THE CODE EXAMPLE TERMINATES HERE AS INTENDED. ***
'
'

Comentários

Uma codificação mapeia um caractere Unicode para uma sequência codificada de bytes, que pode ser posteriormente transferida para um meio físico, como um disco ou por um link de comunicações.An encoding maps a Unicode character to an encoded sequence of bytes, which can subsequently be transferred to a physical medium, such as a disk, or over a communications link. Os caracteres podem ser mapeados de várias maneiras, e uma codificação específica é representada por um tipo derivado Encoding da classe.Characters can be mapped in various ways, and a particular encoding is represented by a type derived from the Encoding class. Especificamente, o método do tipo GetBytes de codificação codifica um caractere em uma sequência de bytes e o GetChars método decodifica uma sequência de bytes para um caractere.Specifically, the encoding type's GetBytes method encodes a character to a byte sequence, and the GetChars method decodes a byte sequence to a character.

Uma operação de decodificação poderá falhar se a sequência de bytes de entrada não puder ser mapeada pela codificação.A decoding operation can fail if the input byte sequence cannot be mapped by the encoding. Por exemplo, um ASCIIEncoding objeto não pode decodificar uma sequência de bytes que produz um caractere com um valor de ponto de código que está fora do intervalo de u + 0000 a u + 007F.For example, an ASCIIEncoding object cannot decode a byte sequence that yields a character having a code point value that is outside the range U+0000 to U+007F.

Nos casos em que uma conversão de codificação ou decodificação não pode ser executada, o .NET Framework fornece um mecanismo de tratamento de falhas chamado de fallback.In cases where an encoding or decoding conversion cannot be performed, the .NET Framework provides a failure-handling mechanism called a fallback. Seu aplicativo pode usar o fallback predefinido .NET Framework decodificador ou pode criar um retorno de decodificador DecoderFallback personalizado DecoderFallbackBuffer derivado das classes e.Your application can use the predefined .NET Framework decoder fallback, or it can create a custom decoder fallback derived from the DecoderFallback and DecoderFallbackBuffer classes.

O .NET Framework fornece duas classes predefinidas que implementam estratégias de fallback diferentes para lidar com falhas de conversão de decodificação.The .NET Framework provides two predefined classes that implement different fallback strategies for handling decoding conversion failures. A DecoderReplacementFallback classe substitui uma cadeia de caracteres fornecida no lugar de qualquer sequência de bytes de entrada que não pode ser convertida.The DecoderReplacementFallback class substitutes a string provided in place of any input byte sequence that cannot be converted. Depois que a cadeia de caracteres substituta é emitida, a operação de decodificação continua convertendo o restante da entrada.After the substitute string is emitted, the decoding operation continues converting the remainder of the input. Por outro lado, DecoderExceptionFallback a classe gera DecoderFallbackException um quando uma sequência de bytes inválida é encontrada.In contrast, the DecoderExceptionFallback class throws a DecoderFallbackException when an invalid byte sequence is encountered.

Construtores

DecoderExceptionFallback() DecoderExceptionFallback() DecoderExceptionFallback() DecoderExceptionFallback()

Inicializa uma nova instância da classe DecoderExceptionFallback.Initializes a new instance of the DecoderExceptionFallback class.

Propriedades

MaxCharCount MaxCharCount MaxCharCount MaxCharCount

Obtém o número máximo de caracteres que esta instância pode retornar.Gets the maximum number of characters this instance can return.

Métodos

CreateFallbackBuffer() CreateFallbackBuffer() CreateFallbackBuffer() CreateFallbackBuffer()

Retorna um buffer de fallback do decodificador que gera uma exceção se não for possível converter uma sequência de bytes em um caractere.Returns a decoder fallback buffer that throws an exception if it cannot convert a sequence of bytes to a character.

Equals(Object) Equals(Object) Equals(Object) Equals(Object)

Indica se o objeto DecoderExceptionFallback atual e um objeto especificado são iguais.Indicates whether the current DecoderExceptionFallback object and a specified object are equal.

GetHashCode() GetHashCode() GetHashCode() GetHashCode()

Recupera o código hash para essa instância.Retrieves the hash code for this instance.

GetType() GetType() GetType() GetType()

Obtém o Type da instância atual.Gets the Type of the current instance.

(Inherited from Object)
MemberwiseClone() MemberwiseClone() MemberwiseClone() MemberwiseClone()

Cria uma cópia superficial do Object atual.Creates a shallow copy of the current Object.

(Inherited from Object)
ToString() ToString() ToString() ToString()

Retorna uma cadeia de caracteres que representa o objeto atual.Returns a string that represents the current object.

(Inherited from Object)

Aplica-se a

Veja também