Encoding.ASCII Proprietà

public:
 static property System::Text::Encoding ^ ASCII { System::Text::Encoding ^ get(); };

public static System.Text.Encoding ASCII { get; }

static member ASCII : System.Text.Encoding

Public Shared ReadOnly Property ASCII As Encoding

Valore della proprietà

Codifica per il set di caratteri ASCII (a 7 bit).

Esempio

Nell'esempio seguente viene illustrato l'effetto della codifica ASCII sui caratteri esterni all'intervallo ASCII.

using System;
using System.Text;

class EncodingExample 
{
  public static void Main() 
  {
      // Create an ASCII encoding.
      Encoding ascii = Encoding.ASCII;
  
      // A Unicode string with two characters outside the ASCII code range.
      String unicodeString =
          "This unicode string contains two characters " +
          "with codes outside the ASCII code range, " +
          "Pi (\u03a0) and Sigma (\u03a3).";
      Console.WriteLine("Original string:");
      Console.WriteLine(unicodeString);

      // Save the positions of the special characters for later reference.
      int indexOfPi = unicodeString.IndexOf('\u03a0');
      int indexOfSigma = unicodeString.IndexOf('\u03a3');

      // Encode the string.
      Byte[] encodedBytes = ascii.GetBytes(unicodeString);
      Console.WriteLine();
      Console.WriteLine("Encoded bytes:");
      foreach (Byte b in encodedBytes) 
      {
          Console.Write("[{0}]", b);
      }
      Console.WriteLine();
  
      // Notice that the special characters have been replaced with
      // the value 63, which is the ASCII character code for '?'.
      Console.WriteLine();
      Console.WriteLine(
          "Value at position of Pi character: {0}",
          encodedBytes[indexOfPi]
          );
      Console.WriteLine(
          "Value at position of Sigma character: {0}",
          encodedBytes[indexOfSigma]
          );

      // Decode bytes back to a string.
      // Notice missing the Pi and Sigma characters.
      String decodedString = ascii.GetString(encodedBytes);
      Console.WriteLine();
      Console.WriteLine("Decoded bytes:");
      Console.WriteLine(decodedString);
  }
}
/*
This code produces the following output.

Original string:
This unicode string contains two characters with codes outside the ASCII code range, Pi (Π) and Sigma (Σ).

Encoded bytes:
[84][104][105][115][32][117][110][105][99][111][100][101][32][115][116][114][105][110][103][32][99][111][110][116][97][105][110][115][32][116][119][111][32][99][104][97][114][97][99][116][101][114][115][32][119][105][116][104][32][99][111][100][101][115][32][111][117][116][115][105][100][101][32][116][104][101][32][65][83][67][73][73][32][99][111][100][101][32][114][97][110][103][101][44][32][80][105][32][40][63][41][32][97][110][100][32][83][105][103][109][97][32][40][63][41][46]

Value at position of Pi character: 63
Value at position of Sigma character: 63

Decoded bytes:
This unicode string contains two characters with codes outside the ASCII code range, Pi (?) and Sigma (?).

*/

Imports System.Text

Class EncodingExample
  Public Shared Sub Main()
      ' Create and ASCII encoding.
      Dim ascii As Encoding = Encoding.ASCII

      ' A Unicode string with two characters outside the ASCII code range.
      Dim unicodeString As String = "This unicode string contains two characters " + "with codes outside the ASCII code range, " + "Pi (" & ChrW(&H03A0) & ") and Sigma (" & ChrW(&H03A3) & ")."
      Console.WriteLine("Original string:")
      Console.WriteLine(unicodeString)

      ' Save the positions of the special characters for later reference.
      Dim indexOfPi As Integer = unicodeString.IndexOf(ChrW(&H03A0))
      Dim indexOfSigma As Integer = unicodeString.IndexOf(ChrW(&H03A3))

      ' Encode the string.
      Dim encodedBytes As Byte() = ascii.GetBytes(unicodeString)
      Console.WriteLine()
      Console.WriteLine("Encoded bytes:")
      For Each b In encodedBytes
          Console.Write("[{0}]", b)
      Next b
      Console.WriteLine()

      ' Notice that the special characters have been replaced with
      ' the value 63, which is the ASCII character code for '?'.
      Console.WriteLine()
      Console.WriteLine("Value at position of Pi character: {0}", encodedBytes(indexOfPi))
      Console.WriteLine("Value at position of Sigma character: {0}", encodedBytes(indexOfSigma))

      ' Decode bytes back to a string.
      ' Notice missing Pi and Sigma characters.
      Dim decodedString As String = ascii.GetString(encodedBytes)
      Console.WriteLine()
      Console.WriteLine("Decoded bytes:")
      Console.WriteLine(decodedString)
  End Sub
End Class
'This code produces the following output.
'Original string:
'This unicode string contains two characters with codes outside the ASCII code range, Pi (Π) and Sigma (Σ).
'
'Encoded bytes:
'[84][104][105][115][32][117][110][105][99][111][100][101][32]'[115][116][114][105][110][103][32][99][111][110][116][97]'[105][110][115][32][116][119][111][32][99][104][97][114][97]'[99][116][101][114][115][32][119][105][116][104][32][99][111]'[100][101][115][32][111][117][116][115][105][100][101][32]'[116][104][101][32][65][83][67][73][73][32][99][111][100]'[101][32][114][97][110][103][101][44][32][80][105][32][40]'[63][41][32][97][110][100][32][83][105][103][109][97][32][40]'[63][41][46]
'
'Value at position of Pi character: 63
'Value at position of Sigma character: 63
'
'Decoded bytes:
'This unicode string contains two characters with codes outside 'the ASCII code range, Pi (?) and Sigma (?).
'

Commenti

I caratteri ASCII sono limitati ai 128 caratteri Unicode più bassi, da U+0000 a U+007F.

Quando si seleziona la codifica ASCII per l'app, considerare quanto segue:

• La codifica ASCII è in genere appropriata per i protocolli che richiedono ASCII.

• Se è necessaria la codifica a 8 bit (talvolta definita erroneamente "ASCII"), è consigliabile usare la codifica UTF-8 tramite la codifica ASCII. Per i caratteri 0-7F, i risultati sono identici, ma l'uso di UTF-8 evita la perdita di dati consentendo la rappresentazione di tutti i caratteri Unicode che sono rappresentabili. Si noti che la codifica ASCII presenta un'ambiguità di 8 bit che può consentire l'uso dannoso, ma la codifica UTF-8 rimuove ambiguità circa l'8° bit.

• Prima di .NET Framework versione 2.0, .NET Framework ha consentito lo spoofing ignorando l'8° bit. A partire da .NET Framework 2.0, i punti di codice non ASCII vengono restituiti durante la decodifica.

L'oggetto ASCIIEncoding restituito da questa proprietà potrebbe non avere il comportamento appropriato per l'app. Usa il fallback sostitutivo per sostituire ogni stringa che non può codificare e ogni byte che non può decodificare con un punto interrogativo ("?"). È invece possibile chiamare il GetEncoding(String, EncoderFallback, DecoderFallback) metodo per creare un'istanza di un ASCIIEncoding oggetto il cui fallback è o EncoderFallbackException , DecoderFallbackExceptioncome illustrato nell'esempio seguente.

using System;
using System.Text;

public class Example
{
   public static void Main()
   {
      Encoding enc = Encoding.GetEncoding("us-ascii", 
                                          new EncoderExceptionFallback(),
                                          new DecoderExceptionFallback());
      string value = "\u00C4 \u00F6 \u00AE"; 
      
      try {
         byte[] bytes= enc.GetBytes(value);
         foreach (var byt in bytes)
            Console.Write("{0:X2} ", byt);
         Console.WriteLine();

         string value2 = enc.GetString(bytes);
         Console.WriteLine(value2);
      }
      catch (EncoderFallbackException e) {
         Console.WriteLine("Unable to encode {0} at index {1}", 
                           e.IsUnknownSurrogate() ? 
                              String.Format("U+{0:X4} U+{1:X4}", 
                                            Convert.ToUInt16(e.CharUnknownHigh),
                                            Convert.ToUInt16(e.CharUnknownLow)) :
                              String.Format("U+{0:X4}", 
                                            Convert.ToUInt16(e.CharUnknown)),
                           e.Index);
      }
   }
}
// The example displays the following output:
//        Unable to encode U+00C4 at index 0

Imports System.Text

Module Example
   Public Sub Main()
      Dim enc As Encoding = Encoding.GetEncoding("us-ascii", 
                                                 New EncoderExceptionFallback(),
                                                 New DecoderExceptionFallback())
      Dim value As String = String.Format("{0} {1} {2}", 
                            ChrW(&h00C4), ChrW(&h00F6), ChrW(&h00AE))
      
      Try
         Dim bytes() As Byte = enc.GetBytes(value)
         For Each byt As Byte In bytes
            Console.Write("{0:X2} ", byt)
         Next       
         Console.WriteLine()
         Dim value2 As String = enc.GetString(bytes)
         Console.WriteLine(value2)
      Catch e As EncoderFallbackException
         Console.WriteLine("Unable to encode {0} at index {1}", 
                           If(e.IsUnknownSurrogate(), 
                              String.Format("U+{0:X4} U+{1:X4}", 
                                            Convert.ToUInt16(e.CharUnknownHigh),
                                            Convert.ToUInt16(e.CharUnknownLow)),
                              String.Format("U+{0:X4}", 
                                            Convert.ToUInt16(e.CharUnknown))),
                           e.Index)
      End Try
   End Sub
End Module
' The example displays the following output:
'       Unable to encode U+00C4 at index 0

Vedi anche

• ASCIIEncoding
• GetEncoding(Int32)
• UTF8
• Unicode
• Come usare le classi di codifica dei caratteri in .NET