DecoderExceptionFallback Класс

Определение

Предоставляет механизм обработки ошибок, называемый резервным вариантом, для закодированной входной последовательности байтов, которая не может быть преобразована во входной символ.Provides a failure-handling mechanism, called a fallback, for an encoded input byte sequence that cannot be converted to an input character. Этот резервный механизм выдает исключение вместо декодирования входной последовательности байтов.The fallback throws an exception instead of decoding the input byte sequence. Этот класс не наследуется.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
Наследование
DecoderExceptionFallback
Атрибуты

Примеры

В следующем примере кода демонстрируются DecoderExceptionFallback классы DecoderFallbackException и.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
'
'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. ***
'
'

Комментарии

В кодировке символ Юникода преобразуется в закодированную последовательность байтов, которая впоследствии может быть передана на физический носитель, например на диск, или через канал связи.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. Символы могут сопоставляться различными способами, а конкретная кодировка представляется типом, производным от Encoding класса.Characters can be mapped in various ways, and a particular encoding is represented by a type derived from the Encoding class. В частности, GetBytes метод типа кодировки кодирует символ в последовательность байтов, GetChars а метод декодирует последовательность байтов в символ.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.

Операция декодирования может завершиться ошибкой, если входная последовательность байтов не может быть сопоставлена с кодировкой.A decoding operation can fail if the input byte sequence cannot be mapped by the encoding. Например, ASCIIEncoding объект не может декодировать последовательность байтов, которая возвращает символ со значением кодовой точки, находящимся за пределами диапазона u + 0000 до 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.

В случаях, когда не удается выполнить преобразование кодирования или декодирования, .NET Framework предоставляет механизм обработки сбоев, называемый откатом.In cases where an encoding or decoding conversion cannot be performed, the .NET Framework provides a failure-handling mechanism called a fallback. Приложение может использовать предопределенный .NET Frameworkный вариант декодера или может создать пользовательский резерв декодера, производный от DecoderFallback классов DecoderFallbackBuffer и.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.

.NET Framework предоставляет два предопределенных класса, которые реализуют различные резервные стратегии для обработки ошибок преобразования декодирования.The .NET Framework provides two predefined classes that implement different fallback strategies for handling decoding conversion failures. DecoderReplacementFallback Класс подставляет строку, указанную вместо любой входной последовательности байтов, которую невозможно преобразовать.The DecoderReplacementFallback class substitutes a string provided in place of any input byte sequence that cannot be converted. После выпуска строки замены операция декодирования продолжит преобразование оставшейся части входных данных.After the substitute string is emitted, the decoding operation continues converting the remainder of the input. В отличие от этого DecoderExceptionFallback , класс DecoderFallbackException создает исключение при обнаружении недопустимой последовательности байтов.In contrast, the DecoderExceptionFallback class throws a DecoderFallbackException when an invalid byte sequence is encountered.

Конструкторы

DecoderExceptionFallback()

Инициализирует новый экземпляр класса DecoderExceptionFallback.Initializes a new instance of the DecoderExceptionFallback class.

Свойства

MaxCharCount

Получает максимальное число символов, которые может вернуть этот экземпляр.Gets the maximum number of characters this instance can return.

Методы

CreateFallbackBuffer()

Возвращает буфер резерва декодера, который выдает исключение, когда не может преобразовать последовательность байтов в символ.Returns a decoder fallback buffer that throws an exception if it cannot convert a sequence of bytes to a character.

Equals(Object)

Указывает, равен ли текущий объект DecoderExceptionFallback указанному объекту.Indicates whether the current DecoderExceptionFallback object and a specified object are equal.

GetHashCode()

Извлекает хэш-код для этого экземпляра.Retrieves the hash code for this instance.

GetType()

Возвращает объект Type для текущего экземпляра.Gets the Type of the current instance.

(Унаследовано от Object)
MemberwiseClone()

Создает неполную копию текущего объекта Object.Creates a shallow copy of the current Object.

(Унаследовано от Object)
ToString()

Возвращает строку, представляющую текущий объект.Returns a string that represents the current object.

(Унаследовано от Object)

Применяется к

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