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Decoder Class

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

System.Object
  System.Text.Decoder

Namespace:  System.Text
Assembly:  mscorlib (in mscorlib.dll)
[SerializableAttribute]
[ComVisibleAttribute(true)]
public abstract class Decoder

The Decoder type exposes the following members.

  NameDescription
Protected methodSupported by the XNA FrameworkSupported by Portable Class LibraryDecoderInitializes a new instance of the Decoder class.
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  NameDescription
Public propertyFallbackGets or sets a DecoderFallback object for the current Decoder object.
Public propertyFallbackBufferGets the DecoderFallbackBuffer object associated with the current Decoder object.
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  NameDescription
Public methodSupported by the XNA FrameworkConvert(Byte*, Int32, Char*, Int32, Boolean, Int32, Int32, Boolean)Converts a buffer of encoded bytes to UTF-16 encoded characters and stores the result in another buffer.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryConvert(Byte[], Int32, Int32, Char[], Int32, Int32, Boolean, Int32, Int32, Boolean)Converts an array of encoded bytes to UTF-16 encoded characters and stores the result in a byte array.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodSupported by the XNA FrameworkSupported by Portable Class LibraryFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodSupported by the XNA FrameworkGetCharCount(Byte*, Int32, Boolean)When overridden in a derived class, calculates the number of characters produced by decoding a sequence of bytes starting at the specified byte pointer. A parameter indicates whether to clear the internal state of the decoder after the calculation.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryGetCharCount(Byte[], Int32, Int32)When overridden in a derived class, calculates the number of characters produced by decoding a sequence of bytes from the specified byte array.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryGetCharCount(Byte[], Int32, Int32, Boolean)When overridden in a derived class, calculates the number of characters produced by decoding a sequence of bytes from the specified byte array. A parameter indicates whether to clear the internal state of the decoder after the calculation.
Public methodSupported by the XNA FrameworkGetChars(Byte*, Int32, Char*, Int32, Boolean)When overridden in a derived class, decodes a sequence of bytes starting at the specified byte pointer and any bytes in the internal buffer into a set of characters that are stored starting at the specified character pointer. A parameter indicates whether to clear the internal state of the decoder after the conversion.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryGetChars(Byte[], Int32, Int32, Char[], Int32)When overridden in a derived class, decodes a sequence of bytes from the specified byte array and any bytes in the internal buffer into the specified character array.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryGetChars(Byte[], Int32, Int32, Char[], Int32, Boolean)When overridden in a derived class, decodes a sequence of bytes from the specified byte array and any bytes in the internal buffer into the specified character array. A parameter indicates whether to clear the internal state of the decoder after the conversion.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodSupported by the XNA FrameworkSupported by Portable Class LibraryMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryResetWhen overridden in a derived class, sets the decoder back to its initial state.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryToStringReturns a string that represents the current object. (Inherited from Object.)
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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. For more information, see Encoding.GetChars. 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);
    }
}


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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