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Encoding.ASCII Property

Gets an encoding for the ASCII (7-bit) character set.

Namespace: System.Text
Assembly: mscorlib (in mscorlib.dll)

public static Encoding ASCII { get; }
/** @property */
public static Encoding get_ASCII ()

public static function get ASCII () : Encoding

Not applicable.

Property Value

A Encoding object for the ASCII (7-bit) character set.

ASCII characters are limited to the lowest 128 Unicode characters, from U+0000 to U+007F.

When selecting the ASCII encoding for your applications, consider the following:

  • The ASCII encoding is usually appropriate for protocols that require ASCII.

  • If your application requires 8-bit encoding, the UTF-8 encoding is recommended over the ASCII encoding. For the characters 0-7F, the results are identical, but use of UTF-8 avoids data loss by allowing representation of all Unicode characters that are representable. Note that the ASCII encoding has an 8th bit ambiguity that can allow malicious use, but the UTF-8 encoding removes ambiguity about the 8th bit.

  • Previous versions of .NET Framework allowed spoofing by ignoring the 8th bit. The current version has been changed so that non-ASCII code points fall back during the decoding of bytes.

For ASCII encoding, the default constructor by itself might not have the appropriate behavior for your application. The application can use EncoderExceptionFallback instead of EncoderFallback and DecoderExceptionFallback instead of DecoderFallback. Use of these classes prevents sequences with the 8th bit set. The application might also use custom behavior for these cases. For more information, see ASCIIEncoding.

The following code example demonstrates the effect of the ASCII encoding on characters that are outside the ASCII range.

using System;
using System.Text;

namespace Encoding_Examples
{
    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);
        }
    }
}

package Encoding_Examples ;

import System.* ;
import System.Text.* ;
import System.Byte;

class EncodingExample
{
    public static void main(String[] args)
    {
        // Create an ASCII encoding.
        Encoding ascii = Encoding.get_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('\u03a0');

        // Encode the string.
        Byte encodedBytes[] = (Byte[])ascii.GetBytes(unicodeString);

        Console.WriteLine();
        Console.WriteLine("Encoded bytes:");

        for (int i = 0; i < encodedBytes.length; i++) {
            Byte b = encodedBytes[i];
            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.get_Item(indexOfPi));
        Console.WriteLine("Value at position of Sigma character: {0}", 
                encodedBytes.get_Item(indexOfSigma));

        // Decode bytes back to a string.
        // Notice missing the Pi and Sigma characters.
        String decodedString = ascii.GetString((ubyte[])encodedBytes);

        Console.WriteLine();
        Console.WriteLine("Decoded bytes:");
        Console.WriteLine(decodedString);
    }
}

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0
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