Decoder Class
Assembly: mscorlib (in mscorlib.dll)
Encoding is the process of transforming a set of 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 characters.
A Decoder maintains state information between successive calls to GetChars 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.
The GetCharCount method determines how many characters result in decoding a sequence of bytes, and the GetChars method performs the actual decoding.
To obtain an instance of an implementation of this class, use the GetDecoder method of an Encoding implementation.
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.
The following code example demonstrates using 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 System.IO.StreamReader 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
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.
