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EncoderExceptionFallback classe

 

Date de publication : novembre 2016

Fournit un mécanisme de gestion d'erreurs, appelé secours, quand un caractère d'entrée ne peut pas être converti en séquence d'octets en sortie. Le secours lève une exception si un caractère d'entrée ne peut pas être converti en séquence d'octets en sortie. Cette classe ne peut pas être héritée.

Espace de noms:   System.Text
Assembly:  mscorlib (dans mscorlib.dll)

System.Object
  System.Text.EncoderFallback
    System.Text.EncoderExceptionFallback

[SerializableAttribute]
public sealed class EncoderExceptionFallback : EncoderFallback

NomDescription
System_CAPS_pubmethodEncoderExceptionFallback()

Initialise une nouvelle instance de la classe EncoderExceptionFallback.

NomDescription
System_CAPS_pubpropertyMaxCharCount

Obtient le nombre maximal de caractères que cette instance peut retourner.(Remplace EncoderFallback.MaxCharCount.)

NomDescription
System_CAPS_pubmethodCreateFallbackBuffer()

Retourne une mémoire tampon de secours d'encodeur qui lève une exception s'il ne peut pas convertir une séquence de caractères en séquence d'octets.(Remplace EncoderFallback.CreateFallbackBuffer().)

System_CAPS_pubmethodEquals(Object)

Indique si l’actuel EncoderExceptionFallback objet et un objet spécifié sont égaux.(Remplace Object.Equals(Object).)

System_CAPS_pubmethodGetHashCode()

Récupère le code de hachage de cette instance.(Remplace Object.GetHashCode().)

System_CAPS_pubmethodGetType()

Obtient le Type de l'instance actuelle.(Hérité de Object.)

System_CAPS_pubmethodToString()

Retourne une chaîne qui représente l'objet actuel.(Hérité de Object.)

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. Characters can be mapped in various ways, and a particular encoding is represented by a type derived from the T:System.Text.Encoding class. 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.

An encoding operation can fail if the input character cannot be represented by the encoding. For example, a T:System.Text.ASCIIEncoding object cannot encode a character that yields a Unicode code point value that is outside the range U+0000 to U+007F.

In cases where an encoding or decoding conversion cannot be performed, the .NET Framework provides a failure-handling mechanism called a fallback. Your application can use the predefined .NET Framework encoder fallback, or it can create a custom encoder fallback derived from the T:System.Text.EncoderFallback and T:System.Text.EncoderFallbackBuffer classes.

The .NET Framework provides two predefined classes that implement different fallback strategies for handling encoding conversion failures. The T:System.Text.EncoderReplacementFallback class substitutes a string provided for any input character that cannot be converted. The substitute string is encoded in place of the invalid character, and then the encoding operation continues converting the remainder of the input. In contrast, the T:System.Text.EncoderExceptionFallback class throws a T:System.Text.EncoderFallbackException when an invalid character is encountered.

The following code example demonstrates the T:System.Text.EncoderExceptionFallback and T:System.Text.EncoderFallbackException classes.

// This example demonstrates the EncoderExceptionFallback 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 EncoderExceptionFallback parameter causes an exception to
// be thrown when a character cannot be encoded. 
// A decoder exception fallback is also specified, but it is not 
// used because this example terminates during the encoding operation.  

    Encoding ae = Encoding.GetEncoding(
                  "us-ascii",
                  new EncoderExceptionFallback(), 
                  new DecoderExceptionFallback());

// The input string consists of the Unicode characters LEFT POINTING 
// DOUBLE ANGLE QUOTATION MARK (U+00AB), 'X' (U+0058), and RIGHT POINTING 
// DOUBLE ANGLE QUOTATION MARK (U+00BB). 
// The encoding can only encode characters in the US-ASCII range of U+0000 
// through U+007F. Consequently, the characters bracketing the 'X' character
// cause an exception.
    string inputString = "\u00abX\u00bb";

    string twoNewLines = "\n\n";
    byte[] encodedBytes = new byte[ae.GetMaxByteCount(inputString.Length)];
    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);

// --------------------------------------------------------------------------
// Attempt to encode the input string. However, an exception is thrown before
// the input string can be encoded.

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

// The code example terminates during the call to the GetBytes() method.
    try {
        numberOfEncodedBytes = ae.GetBytes(inputString, 0, inputString.Length, 
                                           encodedBytes, 0);
        }
    catch (EncoderFallbackException e)
        {
        Console.WriteLine(e);
        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): "�X�"
Input string in hexadecimal: 0xAB 0x58 0xBB

Encode the input string...
System.Text.EncoderFallbackException: Unable to translate Unicode character \u00AB at inde
x 0 to specified code page.
   at System.Text.EncoderExceptionFallbackBuffer.Fallback(Char charUnknown, Int32 index)
   at System.Text.EncoderFallbackBuffer.InternalFallback(Char ch, Char*& chars)
   at System.Text.ASCIIEncoding.GetBytes(Char* chars, Int32 charCount, Byte* bytes, Int32
byteCount, EncoderNLS encoder)
   at System.Text.ASCIIEncoding.GetBytes(String chars, Int32 charIndex, Int32 charCount, B
yte[] bytes, Int32 byteIndex)
   at Sample.Main()

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

*/

Plateforme Windows universelle
Disponible depuis 10
.NET Framework
Disponible depuis 2.0

Tous les membres statiques publics ( Shared en Visual Basic) de ce type sont thread-safe. Les membres d’instance n’ont pas la garantie d’être thread-safe.

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