DecoderReplacementFallback クラス

定義

エンコード済み入力バイト シーケンスを出力文字に変換できない場合のために、フォールバックと呼ばれるエラー処理機構を提供します。Provides a failure-handling mechanism, called a fallback, for an encoded input byte sequence that cannot be converted to an output character. フォールバックは、デコード対象の入力バイト シーケンスの代わりに、ユーザーが指定した置換文字列を作成します。The fallback emits a user-specified replacement string instead of a decoded input byte sequence. このクラスは継承できません。This class cannot be inherited.

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
継承
DecoderReplacementFallback
属性

DecoderReplacementFallback クラスのコード例を次に示します。The following code example demonstrates the DecoderReplacementFallback class.

// 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)"
'

注釈

エンコード操作またはデコード操作が失敗する一般的な理由は、基になるエンコーディングクラスが文字とそれに相当するバイトシーケンスとの間のマッピングを提供しない場合です。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. たとえば、オブジェクトは、 ASCIIEncoding 0x7f よりも大きいバイト値をデコードすることはできません。For example, an ASCIIEncoding object cannot decode a byte value greater than 0x7F. 入力バイトシーケンスを出力文字に変換できない場合、オブジェクトは DecoderReplacementFallback 出力に置換文字列を出力して、元の入力バイトシーケンスを表します。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. 変換処理では、元の入力の残りの部分が引き続きデコードされます。The conversion process then continues to decode the remainder of the original input.

オブジェクトによって使用される置換文字列 DecoderReplacementFallback は、そのクラスコンストラクターの呼び出しによって決定されます。The replacement string used by a DecoderReplacementFallback object is determined by the call to its class constructor. 次の 2 つのオプションを使用できます。Two options are available:

  • 既定の文字に置き換えます。Replacement with the default character. コンストラクターを呼び出すと DecoderReplacementFallback() 、置換文字は "?" になります。(U + 003F)。If you call the DecoderReplacementFallback() constructor, the replacement character is "?" (U+003F).

  • 任意の文字列で置き換えます。Replacement with a string of your choice. コンストラクターを呼び出す場合は、 DecoderReplacementFallback(String) 置換後の文字列を指定します。If you call the DecoderReplacementFallback(String) constructor, you provide the replacement string.

このクラスは2つの .NET Framework クラスのうちの1つであり、デコード変換エラーを処理するための異なるフォールバック戦略を実装します。This class is one of two .NET Framework classes that implement different fallback strategies for handling decoding conversion failures. もう1つのクラスはクラスであり、 DecoderExceptionFallback DecoderFallbackException 無効なバイトシーケンスが検出されたときにをスローします。The other class is the DecoderExceptionFallback class, which throws a DecoderFallbackException when an invalid byte sequence is encountered.

コンストラクター

DecoderReplacementFallback()

DecoderReplacementFallback クラスの新しいインスタンスを初期化します。Initializes a new instance of the DecoderReplacementFallback class.

DecoderReplacementFallback(String)

指定した置換文字列を使用して、DecoderReplacementFallback クラスの新しいインスタンスを初期化します。Initializes a new instance of the DecoderReplacementFallback class using a specified replacement string.

プロパティ

DefaultString

DecoderReplacementFallback オブジェクトの値である置換文字列を取得します。Gets the replacement string that is the value of the DecoderReplacementFallback object.

MaxCharCount

DecoderReplacementFallback オブジェクトの置換文字列に含まれる文字数を取得します。Gets the number of characters in the replacement string for the DecoderReplacementFallback object.

メソッド

CreateFallbackBuffer()

この DecoderFallbackBuffer オブジェクトの置換文字列で初期化される DecoderReplacementFallback オブジェクトを作成します。Creates a DecoderFallbackBuffer object that is initialized with the replacement string of this DecoderReplacementFallback object.

Equals(Object)

指定したオブジェクトの値が、DecoderReplacementFallback オブジェクトと等しいかどうかを示します。Indicates whether the value of a specified object is equal to the DecoderReplacementFallback object.

GetHashCode()

DecoderReplacementFallback オブジェクトの値のハッシュ コードを取得します。Retrieves the hash code for the value of the DecoderReplacementFallback object.

GetType()

現在のインスタンスの Type を取得します。Gets the Type of the current instance.

(継承元 Object)
MemberwiseClone()

現在の Object の簡易コピーを作成します。Creates a shallow copy of the current Object.

(継承元 Object)
ToString()

現在のオブジェクトを表す文字列を返します。Returns a string that represents the current object.

(継承元 Object)

適用対象

こちらもご覧ください