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TextEncoding.h

//
// TextEncoding.h
//
// $Id: //poco/1.3/Foundation/include/Poco/TextEncoding.h#2 $
//
// Library: Foundation
// Package: Text
// Module:  TextEncoding
//
// Definition of the abstract TextEncoding class.
//
// Copyright (c) 2004-2007, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
// 
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#ifndef Foundation_TextEncoding_INCLUDED
#define Foundation_TextEncoding_INCLUDED


#include "Poco/Foundation.h"
#include "Poco/SharedPtr.h"


namespace Poco {


class TextEncodingManager;


00053 class Foundation_API TextEncoding
      /// An abstract base class for implementing text encodings
      /// like UTF-8 or ISO 8859-1. 
      ///
      /// Subclasses must override the canonicalName(), isA(),
      /// characterMap() and convert() methods and need to be
      /// thread safe and stateless.
      ///
      /// TextEncoding also provides static member functions
      /// for managing mappings from encoding names to
      /// TextEncoding objects.
{
public:
      typedef SharedPtr<TextEncoding> Ptr;
      
      enum
      {
            MAX_SEQUENCE_LENGTH = 6 /// The maximum character byte sequence length supported.
      };
      
      typedef int CharacterMap[256];
            /// The map[b] member gives information about byte sequences
            /// whose first byte is b.
            /// If map[b] is c where c is >= 0, then b by itself encodes the Unicode scalar value c.
            /// If map[b] is -1, then the byte sequence is malformed.
            /// If map[b] is -n, where n >= 2, then b is the first byte of an n-byte
            /// sequence that encodes a single Unicode scalar value. Byte sequences up
            /// to 6 bytes in length are supported.

      virtual ~TextEncoding();
            /// Destroys the encoding.

      virtual const char* canonicalName() const = 0;
            /// Returns the canonical name of this encoding,
            /// e.g. "ISO-8859-1". Encoding name comparisons are case
            /// insensitive.

      virtual bool isA(const std::string& encodingName) const = 0;
            /// Returns true if the given name is one of the names of this encoding.
            /// For example, the "ISO-8859-1" encoding is also known as "Latin-1".
            ///
            /// Encoding name comparision are be case insensitive.
                  
      virtual const CharacterMap& characterMap() const = 0;
            /// Returns the CharacterMap for the encoding.
            /// The CharacterMap should be kept in a static member. As
            /// characterMap() can be called frequently, it should be
            /// implemented in such a way that it just returns a static
            /// map. If the map is built at runtime, this should be
            /// done in the constructor.
            
      virtual int convert(const unsigned char* bytes) const;
            /// The convert function is used to convert multibyte sequences;
            /// bytes will point to a byte sequence of n bytes where 
            /// getCharacterMap()[*bytes] == -n.
            ///
            /// The convert function must return the Unicode scalar value
            /// represented by this byte sequence or -1 if the byte sequence is malformed.
            /// The default implementation returns (int) bytes[0].

      virtual int convert(int ch, unsigned char* bytes, int length) const;
            /// Transform the Unicode character ch into the encoding's 
            /// byte sequence. The method returns the number of bytes
            /// used. The method must not use more than length characters.
            /// Bytes and length can also be null - in this case only the number
            /// of bytes required to represent ch is returned.
            /// If the character cannot be converted, 0 is returned and
            /// the byte sequence remains unchanged.
            /// The default implementation simply returns 0.

      static TextEncoding& byName(const std::string& encodingName);
            /// Returns the TextEncoding object for the given encoding name.
            ///
            /// Throws a NotFoundException if the encoding with given name is not available.
            
      static TextEncoding::Ptr find(const std::string& encodingName);
            /// Returns a pointer to the TextEncoding object for the given encodingName,
            /// or NULL if no such TextEncoding object exists.

      static void add(TextEncoding::Ptr encoding);
            /// Adds the given TextEncoding to the table of text encodings,
            /// under the encoding's canonical name.
            ///
            /// If an encoding with the given name is already registered,
            /// it is replaced.

      static void add(TextEncoding::Ptr encoding, const std::string& name);
            /// Adds the given TextEncoding to the table of text encodings,
            /// under the given name.
            ///
            /// If an encoding with the given name is already registered,
            /// it is replaced.

      static void remove(const std::string& encodingName);
            /// Removes the encoding with the given name from the table
            /// of text encodings.

      static TextEncoding::Ptr global(TextEncoding::Ptr encoding);
            /// Sets global TextEncoding object.
            ///
            /// This function sets the global encoding to the argument and returns a
            /// reference of the previous global encoding.

      static TextEncoding& global();
            /// Return the current global TextEncoding object

00159       static const std::string GLOBAL;
            /// Name of the global TextEncoding, which is the empty string.
            
protected:
      static TextEncodingManager& manager();
            /// Returns the TextEncodingManager.
};


} // namespace Poco


#endif // Foundation_TextEncoding_INCLUDED

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