9 our @ISA = qw(Exporter DynaLoader);
11 # Public, encouraged API is exported by default
37 # Documentation moved after __END__ for speed - NI-S
41 # Make a %encoding package variable to allow a certain amount of cheating
43 my @alias; # ordered matching list
44 my %alias; # cached known aliases
46 # 0 1 2 3 4 5 6 7 8 9 10
47 our @latin2iso_num = ( 0, 1, 2, 3, 4, 9, 10, 13, 14, 15, 16 );
65 return keys %encoding;
72 # print "# findAlias $_\n";
73 unless (exists $alias{$_})
75 for (my $i=0; $i < @alias; $i += 2)
77 my $alias = $alias[$i];
78 my $val = $alias[$i+1];
80 if (ref($alias) eq 'Regexp' && $_ =~ $alias)
84 elsif (ref($alias) eq 'CODE')
86 $new = &{$alias}($val)
88 elsif (lc($_) eq lc($alias))
94 next if $new eq $_; # avoid (direct) recursion on bugs
95 my $enc = (ref($new)) ? $new : find_encoding($new);
111 my ($alias,$name) = splice(@_,0,2);
112 push(@alias, $alias => $name);
116 # Allow variants of iso-8859-1 etc.
117 define_alias( qr/^iso[-_]?(\d+)[-_](\d+)$/i => '"iso-$1-$2"' );
119 # At least HP-UX has these.
120 define_alias( qr/^iso8859(\d+)$/i => '"iso-8859-$1"' );
123 define_alias( qr/^(?:hp-)?(arabic|greek|hebrew|kana|roman|thai|turkish)8$/i => '"${1}8"' );
125 # The Official name of ASCII.
126 define_alias( qr/^ANSI[-_]?X3\.4[-_]?1968$/i => '"ascii"' );
128 # This is a font issue, not an encoding issue.
129 # (The currency symbol of the Latin 1 upper half
130 # has been redefined as the euro symbol.)
131 define_alias( qr/^(.+)\@euro$/i => '"$1"' );
133 # Allow latin-1 style names as well
134 define_alias( qr/^(?:iso[-_]?)?latin[-_]?(\d+)$/i => '"iso-8859-$latin2iso_num[$1]"' );
136 # Allow winlatin1 style names as well
137 define_alias( qr/^win(latin[12]|cyrillic|baltic|greek|turkish|hebrew|arabic|baltic|vietnamese)$/i => '"cp$winlatin2cp{\u$1}"' );
139 # Common names for non-latin prefered MIME names
140 define_alias( 'ascii' => 'US-ascii',
141 'cyrillic' => 'iso-8859-5',
142 'arabic' => 'iso-8859-6',
143 'greek' => 'iso-8859-7',
144 'hebrew' => 'iso-8859-8',
145 'thai' => 'iso-8859-11',
146 'tis620' => 'iso-8859-11',
149 # At least AIX has IBM-NNN (surprisingly...) instead of cpNNN.
150 define_alias( qr/^ibm[-_]?(\d\d\d\d?)$/i => '"cp$1"');
152 # Standardize on the dashed versions.
153 define_alias( qr/^utf8$/i => 'utf-8' );
154 define_alias( qr/^koi8r$/i => 'koi8-r' );
155 define_alias( qr/^koi8u$/i => 'koi8-u' );
157 # TODO: HP-UX '8' encodings arabic8 greek8 hebrew8 kana8 thai8 turkish8
158 # TODO: HP-UX '15' encodings japanese15 korean15 roi15
159 # TODO: Cyrillic encoding ISO-IR-111 (useful?)
160 # TODO: Chinese encodings GB18030 GBK Big5-HSKCS EUC-TW
161 # TODO: Armenian encoding ARMSCII-8
162 # TODO: Hebrew encoding ISO-8859-8-1
163 # TODO: Thai encoding TCVN
164 # TODO: Korean encoding Johab
165 # TODO: Vietnamese encodings VISCII VPS
166 # TODO: Japanese encoding JIS (not the same as SJIS)
167 # TODO: Mac Asian+African encodings: Arabic Armenian Bengali Burmese
168 # ChineseSimp ChineseTrad Devanagari Ethiopic ExtArabic
169 # Farsi Georgian Gujarati Gurmukhi Hebrew Japanese
170 # Kannada Khmer Korean Laotian Malayalam Mongolian
171 # Oriya Sinhalese Symbol Tamil Telugu Tibetan Vietnamese
172 # TODO: what is the Japanese 'UJIS' encoding seen in some Linuxes?
174 # Map white space and _ to '-'
175 define_alias( qr/^(\S+)[\s_]+(.*)$/i => '"$1-$2"' );
181 $encoding{$name} = $obj;
183 define_alias($lc => $obj) unless $lc eq $name;
187 define_alias($alias,$obj);
194 my ($class,$name) = @_;
196 if (ref($name) && $name->can('new_sequence'))
201 if (exists $encoding{$name})
203 return $encoding{$name};
205 if (exists $encoding{$lc})
207 return $encoding{$lc};
210 my $oc = $class->findAlias($name);
211 return $oc if defined $oc;
212 return $class->findAlias($lc) if $lc ne $name;
220 return __PACKAGE__->getEncoding($name);
225 my ($name,$string,$check) = @_;
226 my $enc = find_encoding($name);
227 croak("Unknown encoding '$name'") unless defined $enc;
228 my $octets = $enc->encode($string,$check);
229 return undef if ($check && length($string));
235 my ($name,$octets,$check) = @_;
236 my $enc = find_encoding($name);
237 croak("Unknown encoding '$name'") unless defined $enc;
238 my $string = $enc->decode($octets,$check);
239 $_[1] = $octets if $check;
245 my ($string,$from,$to,$check) = @_;
246 my $f = find_encoding($from);
247 croak("Unknown encoding '$from'") unless defined $f;
248 my $t = find_encoding($to);
249 croak("Unknown encoding '$to'") unless defined $t;
250 my $uni = $f->decode($string,$check);
251 return undef if ($check && length($string));
252 $string = $t->encode($uni,$check);
253 return undef if ($check && length($uni));
254 return length($_[0] = $string);
267 return undef unless utf8::decode($str);
271 package Encode::Encoding;
272 # Base class for classes which implement encodings
277 my $canonical = shift;
278 $obj = bless { Name => $canonical },$obj unless ref $obj;
279 # warn "$canonical => $obj\n";
280 Encode::define_encoding($obj, $canonical, @_);
283 sub name { shift->{'Name'} }
285 # Temporary legacy methods
286 sub toUnicode { shift->decode(@_) }
287 sub fromUnicode { shift->encode(@_) }
289 sub new_sequence { return $_[0] }
292 use base 'Encode::Encoding';
294 package Encode::Internal;
295 use base 'Encode::Encoding';
297 # Dummy package that provides the encode interface but leaves data
298 # as UTF-X encoded. It is here so that from_to() works.
300 __PACKAGE__->Define('Internal');
302 Encode::define_alias( 'Unicode' => 'Internal' ) if ord('A') == 65;
306 my ($obj,$str,$chk) = @_;
314 package Encoding::Unicode;
315 use base 'Encode::Encoding';
317 __PACKAGE__->Define('Unicode') unless ord('A') == 65;
321 my ($obj,$str,$chk) = @_;
323 for (my $i = 0; $i < length($str); $i++)
325 $res .= chr(utf8::unicode_to_native(ord(substr($str,$i,1))));
333 my ($obj,$str,$chk) = @_;
335 for (my $i = 0; $i < length($str); $i++)
337 $res .= chr(utf8::native_to_unicode(ord(substr($str,$i,1))));
344 package Encode::utf8;
345 use base 'Encode::Encoding';
346 # package to allow long-hand
347 # $octets = encode( utf8 => $string );
350 __PACKAGE__->Define(qw(UTF-8 utf8));
354 my ($obj,$octets,$chk) = @_;
355 my $str = Encode::decode_utf8($octets);
366 my ($obj,$string,$chk) = @_;
367 my $octets = Encode::encode_utf8($string);
372 package Encode::iso10646_1;
373 use base 'Encode::Encoding';
374 # Encoding is 16-bit network order Unicode (no surogates)
375 # Used for X font encodings
377 __PACKAGE__->Define(qw(UCS-2 iso-10646-1));
381 my ($obj,$str,$chk) = @_;
385 my $code = unpack('n',substr($str,0,2,'')) & 0xffff;
388 $_[1] = $str if $chk;
395 my ($obj,$uni,$chk) = @_;
399 my $ch = substr($uni,0,1,'');
406 $str .= pack('n',$x);
408 $_[1] = $uni if $chk;
412 package Encode::ucs_2le;
413 use base 'Encode::Encoding';
415 __PACKAGE__->Define(qw(UCS-2le UCS-2LE ucs-2le));
419 my ($obj,$str,$chk) = @_;
423 my $code = unpack('v',substr($str,0,2,'')) & 0xffff;
426 $_[1] = $str if $chk;
433 my ($obj,$uni,$chk) = @_;
437 my $ch = substr($uni,0,1,'');
444 $str .= pack('v',$x);
446 $_[1] = $uni if $chk;
450 # switch back to Encode package in case we ever add AutoLoader
459 Encode - character encodings
467 The C<Encode> module provides the interfaces between Perl's strings
468 and the rest of the system. Perl strings are sequences of B<characters>.
470 The repertoire of characters that Perl can represent is at least that
471 defined by the Unicode Consortium. On most platforms the ordinal
472 values of the characters (as returned by C<ord(ch)>) is the "Unicode
473 codepoint" for the character (the exceptions are those platforms where
474 the legacy encoding is some variant of EBCDIC rather than a super-set
475 of ASCII - see L<perlebcdic>).
477 Traditionaly computer data has been moved around in 8-bit chunks
478 often called "bytes". These chunks are also known as "octets" in
479 networking standards. Perl is widely used to manipulate data of
480 many types - not only strings of characters representing human or
481 computer languages but also "binary" data being the machines representation
482 of numbers, pixels in an image - or just about anything.
484 When Perl is processing "binary data" the programmer wants Perl to process
485 "sequences of bytes". This is not a problem for Perl - as a byte has 256
486 possible values it easily fits in Perl's much larger "logical character".
494 I<character>: a character in the range 0..(2**32-1) (or more).
495 (What Perl's strings are made of.)
499 I<byte>: a character in the range 0..255
500 (A special case of a Perl character.)
504 I<octet>: 8 bits of data, with ordinal values 0..255
505 (Term for bytes passed to or from a non-Perl context, e.g. disk file.)
509 The marker [INTERNAL] marks Internal Implementation Details, in
510 general meant only for those who think they know what they are doing,
511 and such details may change in future releases.
515 =head2 Characteristics of an Encoding
517 An encoding has a "repertoire" of characters that it can represent,
518 and for each representable character there is at least one sequence of
519 octets that represents it.
521 =head2 Types of Encodings
523 Encodings can be divided into the following types:
527 =item * Fixed length 8-bit (or less) encodings.
529 Each character is a single octet so may have a repertoire of up to
530 256 characters. ASCII and iso-8859-* are typical examples.
532 =item * Fixed length 16-bit encodings
534 Each character is two octets so may have a repertoire of up to
535 65 536 characters. Unicode's UCS-2 is an example. Also used for
536 encodings for East Asian languages.
538 =item * Fixed length 32-bit encodings.
540 Not really very "encoded" encodings. The Unicode code points
541 are just represented as 4-octet integers. None the less because
542 different architectures use different representations of integers
543 (so called "endian") there at least two disctinct encodings.
545 =item * Multi-byte encodings
547 The number of octets needed to represent a character varies.
548 UTF-8 is a particularly complex but regular case of a multi-byte
549 encoding. Several East Asian countries use a multi-byte encoding
550 where 1-octet is used to cover western roman characters and Asian
551 characters get 2-octets.
552 (UTF-16 is strictly a multi-byte encoding taking either 2 or 4 octets
553 to represent a Unicode code point.)
555 =item * "Escape" encodings.
557 These encodings embed "escape sequences" into the octet sequence
558 which describe how the following octets are to be interpreted.
559 The iso-2022-* family is typical. Following the escape sequence
560 octets are encoded by an "embedded" encoding (which will be one
561 of the above types) until another escape sequence switches to
562 a different "embedded" encoding.
564 These schemes are very flexible and can handle mixed languages but are
565 very complex to process (and have state). No escape encodings are
566 implemented for Perl yet.
570 =head2 Specifying Encodings
572 Encodings can be specified to the API described below in two ways:
578 Encoding names are strings with characters taken from a restricted
579 repertoire. See L</"Encoding Names">.
581 =item 2. As an object
583 Encoding objects are returned by C<find_encoding($name)>.
587 =head2 Encoding Names
589 Encoding names are case insensitive. White space in names is ignored.
590 In addition an encoding may have aliases. Each encoding has one
591 "canonical" name. The "canonical" name is chosen from the names of
592 the encoding by picking the first in the following sequence:
596 =item * The MIME name as defined in IETF RFC-XXXX.
598 =item * The name in the IANA registry.
600 =item * The name used by the the organization that defined it.
604 Because of all the alias issues, and because in the general case
605 encodings have state C<Encode> uses the encoding object internally
606 once an operation is in progress.
608 =head1 PERL ENCODING API
610 =head2 Generic Encoding Interface
616 $bytes = encode(ENCODING, $string[, CHECK])
618 Encodes string from Perl's internal form into I<ENCODING> and returns
619 a sequence of octets. For CHECK see L</"Handling Malformed Data">.
623 $string = decode(ENCODING, $bytes[, CHECK])
625 Decode sequence of octets assumed to be in I<ENCODING> into Perl's
626 internal form and returns the resulting string. For CHECK see
627 L</"Handling Malformed Data">.
631 from_to($string, FROM_ENCODING, TO_ENCODING[, CHECK])
633 Convert B<in-place> the data between two encodings. How did the data
634 in $string originally get to be in FROM_ENCODING? Either using
635 encode() or through PerlIO: See L</"Encoding and IO">. For CHECK
636 see L</"Handling Malformed Data">.
638 For example to convert ISO 8859-1 data to UTF-8:
640 from_to($data, "iso-8859-1", "utf-8");
642 and to convert it back:
644 from_to($data, "utf-8", "iso-8859-1");
646 Note that because the conversion happens in place, the data to be
647 converted cannot be a string constant, it must be a scalar variable.
651 =head2 Handling Malformed Data
653 If CHECK is not set, C<undef> is returned. If the data is supposed to
654 be UTF-8, an optional lexical warning (category utf8) is given. If
655 CHECK is true but not a code reference, dies.
657 It would desirable to have a way to indicate that transform should use
658 the encodings "replacement character" - no such mechanism is defined yet.
660 It is also planned to allow I<CHECK> to be a code reference.
662 This is not yet implemented as there are design issues with what its
663 arguments should be and how it returns its results.
669 Passed remaining fragment of string being processed.
670 Modifies it in place to remove bytes/characters it can understand
671 and returns a string used to represent them.
675 my $ch = substr($_[0],0,1,'');
676 return sprintf("\x{%02X}",ord($ch);
679 This scheme is close to how underlying C code for Encode works, but gives
680 the fixup routine very little context.
684 Passed original string, and an index into it of the problem area, and
685 output string so far. Appends what it will to output string and
686 returns new index into original string. For example:
689 # my ($s,$i,$d) = @_;
690 my $ch = substr($_[0],$_[1],1);
691 $_[2] .= sprintf("\x{%02X}",ord($ch);
695 This scheme gives maximal control to the fixup routine but is more
696 complicated to code, and may need internals of Encode to be tweaked to
697 keep original string intact.
703 Multiple return values rather than in-place modifications.
705 Index into the string could be pos($str) allowing s/\G...//.
711 The Unicode consortium defines the UTF-8 standard as a way of encoding
712 the entire Unicode repertiore as sequences of octets. This encoding is
713 expected to become very widespread. Perl can use this form internaly
714 to represent strings, so conversions to and from this form are
715 particularly efficient (as octets in memory do not have to change,
716 just the meta-data that tells Perl how to treat them).
722 $bytes = encode_utf8($string);
724 The characters that comprise string are encoded in Perl's superset of UTF-8
725 and the resulting octets returned as a sequence of bytes. All possible
726 characters have a UTF-8 representation so this function cannot fail.
730 $string = decode_utf8($bytes [,CHECK]);
732 The sequence of octets represented by $bytes is decoded from UTF-8
733 into a sequence of logical characters. Not all sequences of octets
734 form valid UTF-8 encodings, so it is possible for this call to fail.
735 For CHECK see L</"Handling Malformed Data">.
739 =head2 Other Encodings of Unicode
741 UTF-16 is similar to UCS-2, 16 bit or 2-byte chunks. UCS-2 can only
742 represent 0..0xFFFF, while UTF-16 has a I<surrogate pair> scheme which
743 allows it to cover the whole Unicode range.
745 Surrogates are code points set aside to encode the 0x01000..0x10FFFF
746 range of Unicode code points in pairs of 16-bit units. The I<high
747 surrogates> are the range 0xD800..0xDBFF, and the I<low surrogates>
748 are the range 0xDC00..0xDFFFF. The surrogate encoding is
750 $hi = ($uni - 0x10000) / 0x400 + 0xD800;
751 $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
755 $uni = 0x10000 + ($hi - 0xD8000) * 0x400 + ($lo - 0xDC00);
757 Encode implements big-endian UCS-2 aliased to "iso-10646-1" as that
758 happens to be the name used by that representation when used with X11
761 UTF-32 or UCS-4 is 32-bit or 4-byte chunks. Perl's logical characters
762 can be considered as being in this form without encoding. An encoding
763 to transfer strings in this form (e.g. to write them to a file) would
766 pack('L*', unpack('U*', $string)); # native
768 pack('V*', unpack('U*', $string)); # little-endian
770 pack('N*', unpack('U*', $string)); # big-endian
772 depending on the endianness required.
774 No UTF-32 encodings are implemented yet.
776 Both UCS-2 and UCS-4 style encodings can have "byte order marks" by
777 representing the code point 0xFFFE as the very first thing in a file.
779 =head2 Listing available encodings
781 use Encode qw(encodings);
784 Returns a list of the canonical names of the available encodings.
786 =head2 Defining Aliases
788 use Encode qw(define_alias);
789 define_alias( newName => ENCODING);
791 Allows newName to be used as am alias for ENCODING. ENCODING may be
792 either the name of an encoding or and encoding object (as above).
794 Currently I<newName> can be specified in the following ways:
798 =item As a simple string.
800 =item As a qr// compiled regular expression, e.g.:
802 define_alias( qr/^iso8859-(\d+)$/i => '"iso-8859-$1"' );
804 In this case if I<ENCODING> is not a reference it is C<eval>-ed to
805 allow C<$1> etc. to be subsituted. The example is one way to names as
806 used in X11 font names to alias the MIME names for the iso-8859-*
809 =item As a code reference, e.g.:
811 define_alias( sub { return /^iso8859-(\d+)$/i ? "iso-8859-$1" : undef } , '');
813 In this case C<$_> will be set to the name that is being looked up and
814 I<ENCODING> is passed to the sub as its first argument. The example
815 is another way to names as used in X11 font names to alias the MIME
816 names for the iso-8859-* family.
820 =head2 Defining Encodings
822 use Encode qw(define_alias);
823 define_encoding( $object, 'canonicalName' [,alias...]);
825 Causes I<canonicalName> to be associated with I<$object>. The object
826 should provide the interface described in L</"IMPLEMENTATION CLASSES">
827 below. If more than two arguments are provided then additional
828 arguments are taken as aliases for I<$object> as for C<define_alias>.
830 =head1 Encoding and IO
832 It is very common to want to do encoding transformations when
833 reading or writing files, network connections, pipes etc.
834 If Perl is configured to use the new 'perlio' IO system then
835 C<Encode> provides a "layer" (See L<perliol>) which can transform
836 data as it is read or written.
838 Here is how the blind poet would modernise the encoding:
841 open(my $iliad,'<:encoding(iso-8859-7)','iliad.greek');
842 open(my $utf8,'>:utf8','iliad.utf8');
848 In addition the new IO system can also be configured to read/write
849 UTF-8 encoded characters (as noted above this is efficient):
851 open(my $fh,'>:utf8','anything');
852 print $fh "Any \x{0021} string \N{SMILEY FACE}\n";
854 Either of the above forms of "layer" specifications can be made the default
855 for a lexical scope with the C<use open ...> pragma. See L<open>.
857 Once a handle is open is layers can be altered using C<binmode>.
859 Without any such configuration, or if Perl itself is built using
860 system's own IO, then write operations assume that file handle accepts
861 only I<bytes> and will C<die> if a character larger than 255 is
862 written to the handle. When reading, each octet from the handle
863 becomes a byte-in-a-character. Note that this default is the same
864 behaviour as bytes-only languages (including Perl before v5.6) would
865 have, and is sufficient to handle native 8-bit encodings
866 e.g. iso-8859-1, EBCDIC etc. and any legacy mechanisms for handling
867 other encodings and binary data.
869 In other cases it is the programs responsibility to transform
870 characters into bytes using the API above before doing writes, and to
871 transform the bytes read from a handle into characters before doing
872 "character operations" (e.g. C<lc>, C</\W+/>, ...).
874 You can also use PerlIO to convert larger amounts of data you don't
875 want to bring into memory. For example to convert between ISO 8859-1
876 (Latin 1) and UTF-8 (or UTF-EBCDIC in EBCDIC machines):
878 open(F, "<:encoding(iso-8859-1)", "data.txt") or die $!;
879 open(G, ">:utf8", "data.utf") or die $!;
880 while (<F>) { print G }
882 # Could also do "print G <F>" but that would pull
883 # the whole file into memory just to write it out again.
887 open(my $f, "<:encoding(cp1252)")
888 open(my $g, ">:encoding(iso-8859-2)")
889 open(my $h, ">:encoding(latin9)") # iso-8859-15
891 See L<PerlIO> for more information.
893 See also L<encoding> for how to change the default encoding of the
896 =head1 Encoding How to ...
902 =item * IO with mixed content (faking iso-2020-*)
904 =item * MIME's Content-Length:
906 =item * UTF-8 strings in binary data.
908 =item * Perl/Encode wrappers on non-Unicode XS modules.
912 =head1 Messing with Perl's Internals
914 The following API uses parts of Perl's internals in the current
915 implementation. As such they are efficient, but may change.
919 =item * is_utf8(STRING [, CHECK])
921 [INTERNAL] Test whether the UTF-8 flag is turned on in the STRING.
922 If CHECK is true, also checks the data in STRING for being well-formed
923 UTF-8. Returns true if successful, false otherwise.
925 =item * valid_utf8(STRING)
927 [INTERNAL] Test whether STRING is in a consistent state. Will return
928 true if string is held as bytes, or is well-formed UTF-8 and has the
929 UTF-8 flag on. Main reason for this routine is to allow Perl's
930 testsuite to check that operations have left strings in a consistent
937 [INTERNAL] Turn on the UTF-8 flag in STRING. The data in STRING is
938 B<not> checked for being well-formed UTF-8. Do not use unless you
939 B<know> that the STRING is well-formed UTF-8. Returns the previous
940 state of the UTF-8 flag (so please don't test the return value as
941 I<not> success or failure), or C<undef> if STRING is not a string.
947 [INTERNAL] Turn off the UTF-8 flag in STRING. Do not use frivolously.
948 Returns the previous state of the UTF-8 flag (so please don't test the
949 return value as I<not> success or failure), or C<undef> if STRING is
954 =head1 IMPLEMENTATION CLASSES
956 As mentioned above encodings are (in the current implementation at least)
957 defined by objects. The mapping of encoding name to object is via the
960 The values of the hash can currently be either strings or objects.
961 The string form may go away in the future. The string form occurs
962 when C<encodings()> has scanned C<@INC> for loadable encodings but has
963 not actually loaded the encoding in question. This is because the
964 current "loading" process is all Perl and a bit slow.
966 Once an encoding is loaded then value of the hash is object which
967 implements the encoding. The object should provide the following
974 Should return the string representing the canonical name of the encoding.
976 =item -E<gt>new_sequence
978 This is a placeholder for encodings with state. It should return an
979 object which implements this interface, all current implementations
980 return the original object.
982 =item -E<gt>encode($string,$check)
984 Should return the octet sequence representing I<$string>. If I<$check>
985 is true it should modify I<$string> in place to remove the converted
986 part (i.e. the whole string unless there is an error). If an error
987 occurs it should return the octet sequence for the fragment of string
988 that has been converted, and modify $string in-place to remove the
989 converted part leaving it starting with the problem fragment.
991 If check is is false then C<encode> should make a "best effort" to
992 convert the string - for example by using a replacement character.
994 =item -E<gt>decode($octets,$check)
996 Should return the string that I<$octets> represents. If I<$check> is
997 true it should modify I<$octets> in place to remove the converted part
998 (i.e. the whole sequence unless there is an error). If an error
999 occurs it should return the fragment of string that has been
1000 converted, and modify $octets in-place to remove the converted part
1001 leaving it starting with the problem fragment.
1003 If check is is false then C<decode> should make a "best effort" to
1004 convert the string - for example by using Unicode's "\x{FFFD}" as a
1005 replacement character.
1009 It should be noted that the check behaviour is different from the
1010 outer public API. The logic is that the "unchecked" case is useful
1011 when encoding is part of a stream which may be reporting errors
1012 (e.g. STDERR). In such cases it is desirable to get everything
1013 through somehow without causing additional errors which obscure the
1014 original one. Also the encoding is best placed to know what the
1015 correct replacement character is, so if that is the desired behaviour
1016 then letting low level code do it is the most efficient.
1018 In contrast if check is true, the scheme above allows the encoding to
1019 do as much as it can and tell layer above how much that was. What is
1020 lacking at present is a mechanism to report what went wrong. The most
1021 likely interface will be an additional method call to the object, or
1022 perhaps (to avoid forcing per-stream objects on otherwise stateless
1023 encodings) and additional parameter.
1025 It is also highly desirable that encoding classes inherit from
1026 C<Encode::Encoding> as a base class. This allows that class to define
1027 additional behaviour for all encoding objects. For example built in
1028 Unicode, UCS-2 and UTF-8 classes use :
1030 package Encode::MyEncoding;
1031 use base qw(Encode::Encoding);
1033 __PACKAGE__->Define(qw(myCanonical myAlias));
1035 To create an object with bless {Name => ...},$class, and call
1036 define_encoding. They inherit their C<name> method from
1037 C<Encode::Encoding>.
1039 =head2 Compiled Encodings
1041 F<Encode.xs> provides a class C<Encode::XS> which provides the
1042 interface described above. It calls a generic octet-sequence to
1043 octet-sequence "engine" that is driven by tables (defined in
1044 F<encengine.c>). The same engine is used for both encode and
1045 decode. C<Encode:XS>'s C<encode> forces Perl's characters to their
1046 UTF-8 form and then treats them as just another multibyte
1047 encoding. C<Encode:XS>'s C<decode> transforms the sequence and then
1048 turns the UTF-8-ness flag as that is the form that the tables are
1049 defined to produce. For details of the engine see the comments in
1052 The tables are produced by the Perl script F<compile> (the name needs
1053 to change so we can eventually install it somewhere). F<compile> can
1054 currently read two formats:
1060 This is a coined format used by Tcl. It is documented in
1061 Encode/EncodeFormat.pod.
1065 This is the semi-standard format used by IBM's ICU package.
1069 F<compile> can write the following forms:
1075 See above - the F<Encode/*.ucm> files provided with the distribution have
1076 been created from the original Tcl .enc files using this approach.
1080 Produces tables as C data structures - this is used to build in encodings
1081 into F<Encode.so>/F<Encode.dll>.
1085 In theory this allows encodings to be stand-alone loadable Perl
1086 extensions. The process has not yet been tested. The plan is to use
1087 this approach for large East Asian encodings.
1091 The set of encodings built-in to F<Encode.so>/F<Encode.dll> is
1092 determined by F<Makefile.PL>. The current set is as follows:
1096 =item ascii and iso-8859-*
1098 That is all the common 8-bit "western" encodings.
1100 =item IBM-1047 and two other variants of EBCDIC.
1102 These are the same variants that are supported by EBCDIC Perl as
1103 "native" encodings. They are included to prove "reversibility" of
1104 some constructs in EBCDIC Perl.
1106 =item symbol and dingbats as used by Tk on X11.
1108 (The reason Encode got started was to support Perl/Tk.)
1112 That set is rather ad hoc and has been driven by the needs of the
1113 tests rather than the needs of typical applications. It is likely
1118 L<perlunicode>, L<perlebcdic>, L<perlfunc/open>, L<PerlIO>, L<encoding>