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ASCIIEncoding Class

Represents an ASCII character encoding of Unicode characters.

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

[SerializableAttribute] 
[ComVisibleAttribute(true)] 
public class ASCIIEncoding : Encoding
/** @attribute SerializableAttribute() */ 
/** @attribute ComVisibleAttribute(true) */ 
public class ASCIIEncoding extends Encoding
SerializableAttribute 
ComVisibleAttribute(true) 
public class ASCIIEncoding extends Encoding

Encoding is the process of transforming a set of Unicode characters into a sequence of bytes. Decoding is the reverse; it is the process of transforming a sequence of encoded bytes into a set of Unicode characters.

The Unicode Standard assigns a code point (a number) to each character in every supported script. A Unicode Transformation Format (UTF) is a way to encode that code point. The Unicode Standard version 3.2 uses the following UTFs:

  • UTF-8, which represents each code point as a sequence of one to four bytes.

  • UTF-16, which represents each code point as a sequence of one to two 16-bit integers.

  • UTF-32, which represents each code point as a 32-bit integer.

Caution noteCaution

ASCIIEncoding does not provide error detection. For security reasons, it is recommended that you use UTF8Encoding, UnicodeEncoding, or UTF32Encoding and enable error detection.

NoteNote

ASCIIEncoding supports only the Unicode character values between U+0000 and U+007F. Therefore, UTF8Encoding, UnicodeEncoding, and UTF32Encoding are better suited for globalized applications.

The GetByteCount method determines how many bytes result in encoding a set of Unicode characters, and the GetBytes method performs the actual encoding.

Likewise, the GetCharCount method determines how many characters result in decoding a sequence of bytes, and the GetChars and GetString methods perform the actual decoding.

ASCIIEncoding corresponds to the Windows code page 20127.

The following example demonstrates how to encode Unicode characters into ASCII. Notice the loss of data that occurs when you use ASCIIEncoding to encode Unicode characters outside of the ASCII range.

using System;
using System.Text;

class ASCIIEncodingExample {
    public static void Main() {
        // The encoding.
        ASCIIEncoding ascii = new ASCIIEncoding();
        
        // 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 positions of the special characters for later reference.
        int indexOfPi = unicodeString.IndexOf('\u03a0');
        int indexOfSigma = unicodeString.IndexOf('\u03a3');

        // Encode 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 string.
        // Notice missing Pi and Sigma characters.
        String decodedString = ascii.GetString(encodedBytes);
        Console.WriteLine();
        Console.WriteLine("Decoded bytes:");
        Console.WriteLine(decodedString);
    }
}

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

class ASCIIEncodingExample
{
    public static void main(String[] args)
    {
        // The encoding.
        ASCIIEncoding ascii = new ASCIIEncoding();

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

        // Encode string.
        ubyte encodedBytes[] = ascii.GetBytes(unicodeString);
        Console.WriteLine();
        Console.WriteLine("Encoded bytes:");
        for(int iCtr = 0; iCtr < encodedBytes.length; iCtr++) {
            ubyte b = encodedBytes[iCtr];
            Console.Write("[{0}]", String.valueOf((Byte)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 string.
        // Notice missing Pi and Sigma characters.
        String decodedString = ascii.GetString((ubyte[])encodedBytes);
        Console.WriteLine();
        Console.WriteLine("Decoded bytes:");
        Console.WriteLine(decodedString);
    } //main
} //ASCIIEncodingExample

System.Object
   System.Text.Encoding
    System.Text.ASCIIEncoding

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows 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 .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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