Add a function to perform simple character mapping

[libs/core.git] / source / codec.h

diff --git a/source/codec.h b/source/codec.h
index bed3d93cb2c3e1f245492c4eec43e8db4ef65c58..3470ccc68e6c65ad4890f499a54b41c88fa91256 100644 (file)
--- a/source/codec.h
+++ b/source/codec.h
@@ -39,38 +39,83 @@ public:
 Base class for string codecs.  Use one of the derived classes or the function
 create_codec to create a specific codec.
 
-For the purposes of this class, an ustring is considered to contain
-Unicode characters and an std::string is considered to be an encoded sequence
-of bytes.  A codec is able to determine if an encoded string could be decoded
-with it.
+Unicode strings are represented as ustrings.  An std::string is considered to
+be an encoded sequence of bytes.  A codec is able to determine if an encoded
+string could be decoded with it.
 */
 class Codec
 {
 public:
        /**
-       Base class for string encoder.  Each codec class should contain an Encoder
-       class derived from this.
+       Base class for string encoder.
+
+       Each codec class should contain an Encoder class derived from this.  The
+       encode_char and transliterate functions must be overloaded.  Some encoders
+       may find it useful or necessary to implement some other functions too
+       (particularly sync and reset for stateful codecs).
        */
        class Encoder
        {
        public:
                virtual ~Encoder() { }
 
+               /**
+               Encodes a single unicode character.  If the character can't be
+               represented in this encoding, behavior depends on the error mode
+               specified for the encoder:
+
+               For THROW_ON_ERROR, an exception is thrown.
+
+               For IGNORE_ERRORS, nothing is done.
+
+               For TRANSLITERATE, the encoder attempts to select a character or a string
+               or characters that closely approximates the non-representable character.
+               */
                virtual void encode_char(UnicodeChar ch, std::string &buf) =0;
+
+               /**
+               Encodes a unicode string.  This is equivalent to callind encode_char for
+               each character in the string with the same buffer.
+               */
                virtual void encode(const ustring &str, std::string &buf);
+
+               /**
+               Procuces a sequence of bytes that will bring the encoder back to the
+               initial state.
+               */
                virtual void sync(std::string &buf) { (void)buf; }
+
+               /**
+               Resets the encoder to the initial state without producing output.
+               */
                virtual void reset() { }
        protected:
                ErrorMode err_mode;
 
                Encoder(ErrorMode em): err_mode(em) { }
-               void error(UnicodeChar, std::string &, const std::string &);
-               virtual void transliterate(UnicodeChar, std::string &) { }
+
+               /**
+               Handles an error depending on the error mode.
+
+               For THROW_ON_ERROR, throws CodecError(msg).
+
+               For IGNORE_ERROR, does nothing.
+
+               For TRANSLITERATE, calls transliterate(ch, buf).
+               */
+               void error(UnicodeChar ch, std::string &buf, const std::string &msg);
+
+               /**
+               Attempts to produce an alternative encoding for a unicode character.
+               Typically this includes dropping accent marks or romanizing letters.
+               */
+               virtual void transliterate(UnicodeChar ch, std::string &buf) =0;
        };
 
        /**
-       Base class for string decoder.  Each codec class should contain an Decoder
-       class derived from this.
+       Base class for string decoder.
+
+       Each codec class should contain an Decoder class derived from this.
        */
        class Decoder
        {
@@ -93,12 +138,23 @@ public:
                */
                virtual UnicodeChar decode_char(const std::string &str, std::string::const_iterator &i) =0;
 
+               /**
+               Decodes a string.
+               */
                virtual void decode(const std::string &str, ustring &buf);
+
+               /**
+               Resets the decoder to the initial state.
+               */
                virtual void reset() { }
        protected:
                ErrorMode err_mode;
 
                Decoder(ErrorMode em): err_mode(em) { }
+
+               /**
+               Handles an error depending on the error mode.
+               */
                UnicodeChar error(const std::string &);
        };
 
@@ -129,7 +185,7 @@ typedef Codec::Encoder Encoder;
 typedef Codec::Decoder Decoder;
 
 /**
-Convenience function that decodes a string using the given codec.
+Convenience function that decodes a string.
 */
 template<class C>
 ustring decode(const std::string &s)
@@ -140,6 +196,9 @@ ustring decode(const std::string &s)
        return result;
 }
 
+/**
+Convenience function that encodes a string.
+*/
 template<class C>
 std::string encode(const ustring &s)
 {
@@ -150,6 +209,9 @@ std::string encode(const ustring &s)
        return result;
 }
 
+/**
+Convenience function that transcodes a string from one codec to another.
+*/
 template<class F, class T>
 std::string transcode(const std::string &s)
 {