DecoderReplacementFallback Classe

Définition

Fournit un mécanisme de gestion des erreurs, appelé secours, quand une séquence d'octets codée en entrée ne peut pas être convertie en un caractère de sortie. Le secours émet une chaîne de remplacement définie par l'utilisateur au lieu d'une séquence d'octets décodée en entrée. Cette classe ne peut pas être héritée.

public ref class DecoderReplacementFallback sealed : System::Text::DecoderFallback
public sealed class DecoderReplacementFallback : System.Text.DecoderFallback
[System.Serializable]
public sealed class DecoderReplacementFallback : System.Text.DecoderFallback
type DecoderReplacementFallback = class
    inherit DecoderFallback
[<System.Serializable>]
type DecoderReplacementFallback = class
    inherit DecoderFallback
Public NotInheritable Class DecoderReplacementFallback
Inherits DecoderFallback
Héritage
DecoderReplacementFallback
Attributs

Exemples

L’exemple de code suivant illustre la DecoderReplacementFallback classe.

// This example demonstrates the DecoderReplacementFallback class.

using namespace System;
using namespace System::Text;

int 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.  

    Encoding^ asciiEncoding = Encoding::GetEncoding("us-ascii",
        gcnew EncoderReplacementFallback("(unknown)"),
        gcnew DecoderReplacementFallback("(error)"));
    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);

    // ---------------------------------------------------------------------
    // Decode the encoded bytes.

    Console::WriteLine("Compare the decoded bytes to the input string...");
    decodedString = asciiEncoding->GetString(encodedBytes);

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

*/
// This example demonstrates the DecoderReplacementFallback 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 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.

    Encoding ae = Encoding.GetEncoding(
                  "us-ascii",
                  new EncoderReplacementFallback("(unknown)"),
                  new DecoderReplacementFallback("(error)"));
    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);

// --------------------------------------------------------------------------
// 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);
    }
}
/*
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)"

*/
' This example demonstrates the DecoderReplacementFallback class.
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
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...
'Input string:  "XYZ"
'Decoded string:"(error)Y(error)"
'

Remarques

Une raison courante pour une opération d’encodage ou de décodage échoue si la classe d’encodage sous-jacente ne fournit pas de mappage entre un caractère et une séquence d’octets équivalente. Par exemple, un ASCIIEncoding objet ne peut pas décoder une valeur d’octet supérieure à 0x7F. Si une séquence d’octets d’entrée ne peut pas être convertie en caractère de sortie, un DecoderReplacementFallback objet émet une chaîne de remplacement dans la sortie pour représenter la séquence d’octets d’entrée d’origine. Le processus de conversion continue ensuite à décoder le reste de l’entrée d’origine.

La chaîne de remplacement utilisée par un DecoderReplacementFallback objet est déterminée par l’appel à son constructeur de classe. Deux options sont disponibles :

  • Remplacez par le caractère par défaut. Si vous appelez le DecoderReplacementFallback() constructeur, le caractère de remplacement est « ? » (U+003F).

  • Remplacez par une chaîne de votre choix. Si vous appelez le DecoderReplacementFallback(String) constructeur, vous fournissez la chaîne de remplacement.

Cette classe est l’une des deux classes .NET Framework qui implémentent différentes stratégies de secours pour gérer les échecs de conversion de décodage. L’autre classe est la DecoderExceptionFallback classe, qui lève une DecoderFallbackException séquence d’octets non valide.

Constructeurs

DecoderReplacementFallback()

Initialise une nouvelle instance de la classe DecoderReplacementFallback.

DecoderReplacementFallback(String)

Initialise une nouvelle instance de la classe DecoderReplacementFallback à l'aide de la chaîne de remplacement spécifiée.

Propriétés

DefaultString

Obtient la chaîne de replacement représentant la valeur de l'objet DecoderReplacementFallback.

MaxCharCount

Obtient le nombre de caractères dans la chaîne de remplacement de l'objet DecoderReplacementFallback.

Méthodes

CreateFallbackBuffer()

Crée un objet DecoderFallbackBuffer qui est initialisé avec la chaîne de remplacement de l'objet DecoderReplacementFallback.

Equals(Object)

Indique si la valeur d'un objet spécifié est égale à l'objet DecoderReplacementFallback.

GetHashCode()

Récupère le code de hachage correspondant à la valeur de l'objet DecoderReplacementFallback.

GetType()

Obtient le Type de l'instance actuelle.

(Hérité de Object)
MemberwiseClone()

Crée une copie superficielle du Object actuel.

(Hérité de Object)
ToString()

Retourne une chaîne qui représente l'objet actuel.

(Hérité de Object)

S’applique à

Voir aussi