EncoderExceptionFallback 類別

定義

針對無法轉換為輸出位元組序列的輸入字元,提供失敗處理機制 (稱為後援)。Provides a failure-handling mechanism, called a fallback, for an input character that cannot be converted to an output byte sequence. 如果輸入字元無法轉換成輸出位元組序列,後援會擲回例外狀況。The fallback throws an exception if an input character cannot be converted to an output byte sequence. 此類別無法獲得繼承。This class cannot be inherited.

public ref class EncoderExceptionFallback sealed : System::Text::EncoderFallback
public sealed class EncoderExceptionFallback : System.Text.EncoderFallback
[System.Serializable]
public sealed class EncoderExceptionFallback : System.Text.EncoderFallback
type EncoderExceptionFallback = class
    inherit EncoderFallback
[<System.Serializable>]
type EncoderExceptionFallback = class
    inherit EncoderFallback
Public NotInheritable Class EncoderExceptionFallback
Inherits EncoderFallback
繼承
EncoderExceptionFallback
屬性

範例

下列程式碼範例示範 EncoderExceptionFallbackEncoderFallbackException 類別。The following code example demonstrates the EncoderExceptionFallback and EncoderFallbackException classes.

// This example demonstrates the EncoderExceptionFallback class.

using namespace System;
using namespace System::Text;

int 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^ asciiEncoding = Encoding::GetEncoding("us-ascii",
        gcnew EncoderExceptionFallback(), gcnew 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 = L"\u00abX\u00bb";

    String^ twoNewLines = Environment::NewLine + Environment::NewLine;
    array<Byte>^ encodedBytes = gcnew array<Byte>(
        asciiEncoding->GetMaxByteCount(inputString->Length));
    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);

    // ---------------------------------------------------------------------
    // 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 = asciiEncoding->GetBytes(inputString, 0,
            inputString->Length, encodedBytes, 0);
        // This statement is never executed.
        Console::WriteLine("This statement is never executed.");
    }
    catch (EncoderFallbackException^ 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): "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. ***

*/
// 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. ***

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

Class Sample
    Public Shared Sub 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.  


        Dim eef As New EncoderExceptionFallback()
        Dim def As New DecoderExceptionFallback()
        Dim ae As Encoding = Encoding.GetEncoding("us-ascii", eef, def)
        
        ' 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.

        Dim inputString As String = "«X»"
        
        Dim twoNewLines As String = vbCrLf & vbCrLf
        Dim numberOfEncodedBytes As Integer = ae.GetMaxByteCount(inputString.Length)
        ' 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)
        
        ' --------------------------------------------------------------------------
        ' 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 e As EncoderFallbackException
            Console.WriteLine(e)
            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): "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. ***
'

備註

編碼方式會將 Unicode 字元對應至編碼的位元組序列,之後可以傳輸到實體媒體(例如磁片),或透過通訊連結。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. 您可以使用各種方式來對應字元,並以衍生自類別的型別來表示特定的編碼方式 EncodingCharacters can be mapped in various ways, and a particular encoding is represented by a type derived from the Encoding class. 具體而言,編碼類型的 GetBytes 方法會將字元編碼為位元組序列,而方法會將 GetChars 位元組序列解碼為字元。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.

如果編碼方式無法表示輸入字元,編碼作業可能會失敗。An encoding operation can fail if the input character cannot be represented by the encoding. 例如, ASCIIEncoding 物件無法編碼產生 Unicode 代碼點值的字元,此值位於 u + 0000 到 U + 007F 的範圍之外。For example, a ASCIIEncoding object cannot encode a character that yields a Unicode code point value that is outside the range U+0000 to U+007F.

在無法執行編碼或解碼轉換的情況下,.NET Framework 會提供稱為回復的失敗處理機制。In cases where an encoding or decoding conversion cannot be performed, the .NET Framework provides a failure-handling mechanism called a fallback. 您的應用程式可以使用預先定義的 .NET Framework 編碼器回復,也可以建立衍生自和類別的自訂編碼器回退 EncoderFallback EncoderFallbackBufferYour application can use the predefined .NET Framework encoder fallback, or it can create a custom encoder fallback derived from the EncoderFallback and EncoderFallbackBuffer classes.

.NET Framework 提供兩個預先定義的類別,可執行不同的回溯策略來處理編碼轉換失敗。The .NET Framework provides two predefined classes that implement different fallback strategies for handling encoding conversion failures. EncoderReplacementFallback類別會替代針對無法轉換的任何輸入字元所提供的字串。The EncoderReplacementFallback class substitutes a string provided for any input character that cannot be converted. 替代字串會編碼來取代不正確字元,然後編碼作業會繼續轉換輸入的其餘部分。The substitute string is encoded in place of the invalid character, and then the encoding operation continues converting the remainder of the input. 相反地, EncoderExceptionFallback EncoderFallbackException 當遇到不正確字元時,類別會擲回。In contrast, the EncoderExceptionFallback class throws a EncoderFallbackException when an invalid character is encountered.

建構函式

EncoderExceptionFallback()

初始化 EncoderExceptionFallback 類別的新執行個體。Initializes a new instance of the EncoderExceptionFallback class.

屬性

MaxCharCount

取得這個執行個體可以傳回的最大字元數。Gets the maximum number of characters this instance can return.

方法

CreateFallbackBuffer()

傳回編碼器後援緩衝區,它會在無法將字元序列轉換成位元組序列時擲回例外狀況。Returns an encoder fallback buffer that throws an exception if it cannot convert a character sequence to a byte sequence.

Equals(Object)

指示目前的 EncoderExceptionFallback 物件和指定的物件是否相等。Indicates whether the current EncoderExceptionFallback object and a specified object are equal.

GetHashCode()

擷取這個執行個體的雜湊碼。Retrieves the hash code for this instance.

GetType()

取得目前執行個體的 TypeGets the Type of the current instance.

(繼承來源 Object)
MemberwiseClone()

建立目前 Object 的淺層複製。Creates a shallow copy of the current Object.

(繼承來源 Object)
ToString()

傳回代表目前物件的字串。Returns a string that represents the current object.

(繼承來源 Object)

適用於

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