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Decoder Class

Converts a sequence of encoded bytes into a set of characters.

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

[SerializableAttribute] 
[ComVisibleAttribute(true)] 
public abstract class Decoder
/** @attribute SerializableAttribute() */ 
/** @attribute ComVisibleAttribute(true) */ 
public abstract class Decoder
SerializableAttribute 
ComVisibleAttribute(true) 
public abstract class Decoder
Not applicable.

To obtain an instance of an implementation of the Decoder class, the application should use the GetDecoder method of an Encoding implementation.

The GetCharCount method determines how many characters result in decoding a sequence of bytes, and the GetChars method performs the actual decoding. There are several versions of both of these methods available in the Decoder class.

A Decoder object maintains state information between successive calls to GetChars or Convert methods so it can correctly decode byte sequences that span blocks. The Decoder also preserves trailing bytes at the end of data blocks and uses the trailing bytes in the next decoding operation. Therefore, GetDecoder and GetEncoder are useful for network transmission and file operations because those operations often deal with blocks of data instead of a complete data stream.

NoteNote:

When the application is done with a stream of data, it should make sure that the state information is flushed by setting the flush parameter to true in the appropriate method call. If an exception occurs or if the application switches streams, it should call Reset to clear the internal state of the Decoder object.

Version Considerations

A Decoder or Encoder object can be serialized during a conversion operation. The state of the object is retained if it is deserialized in the same version of the .NET Framework, but lost if it is deserialized in another version.

Notes to Inheritors: When your application inherits from this class, it must override all the members.

The following example demonstrates the use of a Decoder to convert two different byte arrays into a character array. One of the character's bytes spans the arrays. This is similar to what a StreamReader object does internally when reading a stream.

using System;
using System.Text;
public class dec
{
    public static void Main()
    {
        // These bytes in UTF-8 correspond to 3 different Unicode
        // characters: space (U+0020), # (U+0023), and the biohazard
        // symbol (U+2623).  Note the biohazard symbol requires 3 bytes
        // in UTF-8 (hexadecimal e2, 98, a3).  Decoders store state across
        // multiple calls to GetChars, handling the case when one char
        // is in multiple byte arrays.
        byte[] bytes1 = { 0x20, 0x23, 0xe2 };
        byte[] bytes2 = { 0x98, 0xa3 };
        char[] chars = new char[3];

        Decoder d = Encoding.UTF8.GetDecoder();
        int charLen = d.GetChars(bytes1, 0, bytes1.Length, chars, 0);
        // The value of charLen should be 2 now.
        charLen += d.GetChars(bytes2, 0, bytes2.Length, chars, charLen);
        foreach(char c in chars)
            Console.Write("U+{0:X4}  ", (ushort)c);
    }
}

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

public class Dec
{
    public static void main(String[] args)
    {
        // These bytes in UTF-8 correspond to 3 different Unicode
        // characters: space (U+0020), # (U+0023), and the biohazard
        // symbol (U+2623).  Note the biohazard symbol requires 3 bytes
        // in UTF-8 (hexadecimal e2, 98, a3).  Decoders store state across
        // multiple calls to GetChars, handling the case when one char
        // is in multiple byte arrays.
        ubyte bytes1[] =  { 0x20, 0x23, 0xE2 };
        ubyte bytes2[] =  { 0x98, 0xA3 };
        char chars[] = new char[3];
        
        Decoder d = Encoding.get_UTF8().GetDecoder();
        int charLen = d.GetChars(bytes1, 0, bytes1.length, chars, 0);
        
        // The value of charLen should be 2 now.
        charLen += d.GetChars(bytes2, 0, bytes2.length, chars, charLen);

        for (int iCtr = 0; iCtr < chars.length; iCtr++) {
            char c = chars[iCtr];
            Console.Write("U+{0}  ",((Int16)c).ToString("X4"));
        }
    } //main
} //Dec

System.Object
  System.Text.Decoder
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 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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