Encoding.ASCII Vlastnost

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

Hodnota vlastnosti

Kódování pro znakovou sadu ASCII (7bitová verze).

Příklady

Následující příklad ukazuje účinek kódování ASCII na znaky, které jsou mimo rozsah ASCII.

using namespace System;
using namespace System::Text;
using namespace System::Collections;
int main()
{
   
   // Create an ASCII encoding.
   Encoding^ ascii = Encoding::ASCII;
   
   // A Unicode String* with two characters outside the ASCII code range.
   String^ unicodeString = L"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( L'\u03a0' );
   int indexOfSigma = unicodeString->IndexOf( L'\u03a3' );
   
   // Encode the String*.
   array<Byte>^encodedBytes = ascii->GetBytes( unicodeString );
   Console::WriteLine();
   Console::WriteLine( "Encoded bytes:" );
   IEnumerator^ myEnum = encodedBytes->GetEnumerator();
   while ( myEnum->MoveNext() )
   {
      Byte b = safe_cast<Byte>(myEnum->Current);
      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 String*.
   // Notice the missing 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 (?).

*/

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 (?).
'

Poznámky

Znaky ASCII jsou omezeny na nejnižších 128 znaků Unicode, od U+0000 do U+007F.

Při výběru kódování ASCII pro vaši aplikaci zvažte následující:

• Kódování ASCII je obvykle vhodné pro protokoly, které vyžadují ASCII.

• Pokud požadujete 8bitové kódování (které se někdy nesprávně označuje jako "ASCII"), doporučuje se kódování UTF-8 před kódováním ASCII. Pro znaky 0–7F jsou výsledky identické, ale použití UTF-8 zabraňuje ztrátě dat tím, že umožňuje reprezentaci všech znaků Unicode, které jsou reprezentovatelné. Všimněte si, že kódování ASCII má 8bitovou nejednoznačnost, která umožňuje škodlivé použití, ale kódování UTF-8 odstraňuje nejednoznačnost ohledně 8. bitu.

• Před rozhraním .NET Framework verze 2.0 umožňovalo rozhraní .NET Framework falšování identity ignorováním 8. bitu. Počínaje rozhraním .NET Framework 2.0 se body kódu, které nejsou ASCII, při dekódování vrací zpět.

Objekt ASCIIEncoding vrácený touto vlastností nemusí mít odpovídající chování pro vaši aplikaci. Používá náhradní náhradní k nahrazení každého řetězce, který nemůže kódovat, a každý bajt, který nemůže dekódovat, znakem otazníku ("?"). Místo toho můžete volat metodu GetEncoding(String, EncoderFallback, DecoderFallback) pro vytvoření instance objektu ASCIIEncoding , jehož záložní objekt je buď EncoderFallbackException , nebo DecoderFallbackException, jak je znázorněno v následujícím příkladu.

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

Platí pro

Viz také

• ASCIIEncoding
• GetEncoding(Int32)
• UTF8
• Unicode
• Použití tříd kódování znaků v .NET