3 our $VERSION = do { my @r = (q$Revision: 0.90 $ =~ /\d+/g); sprintf "%d."."%02d" x $#r, @r };
8 our @ISA = qw(Exporter DynaLoader);
10 # Public, encouraged API is exported by default
36 # Documentation moved after __END__ for speed - NI-S
40 # Make a %encoding package variable to allow a certain amount of cheating
42 my @alias; # ordered matching list
43 my %alias; # cached known aliases
45 # 0 1 2 3 4 5 6 7 8 9 10
46 our @latin2iso_num = ( 0, 1, 2, 3, 4, 9, 10, 13, 14, 15, 16 );
60 our %external_tables =
62 'euc-cn' => 'Encode/CN.pm',
63 gb2312 => 'Encode/CN.pm',
64 gb12345 => 'Encode/CN.pm',
65 gbk => 'Encode/CN.pm',
66 cp936 => 'Encode/CN.pm',
67 'iso-ir-165' => 'Encode/CN.pm',
68 'euc-jp' => 'Encode/JP.pm',
69 'iso-2022-jp' => 'Encode/JP.pm',
70 '7bit-jis' => 'Encode/JP.pm',
71 shiftjis => 'Encode/JP.pm',
72 macjapan => 'Encode/JP.pm',
73 cp932 => 'Encode/JP.pm',
74 'euc-kr' => 'Encode/KR.pm',
75 ksc5601 => 'Encode/KR.pm',
76 cp949 => 'Encode/KR.pm',
77 big5 => 'Encode/TW.pm',
78 'big5-hkscs' => 'Encode/TW.pm',
79 cp950 => 'Encode/TW.pm',
80 gb18030 => 'Encode/HanExtra.pm',
81 big5plus => 'Encode/HanExtra.pm',
82 'euc-tw' => 'Encode/HanExtra.pm',
90 sort { $a->[1] cmp $b->[1] }
92 grep { $_ ne 'Internal' }
100 # print "# findAlias $_\n";
101 unless (exists $alias{$_})
103 for (my $i=0; $i < @alias; $i += 2)
105 my $alias = $alias[$i];
106 my $val = $alias[$i+1];
108 if (ref($alias) eq 'Regexp' && $_ =~ $alias)
112 elsif (ref($alias) eq 'CODE')
114 $new = &{$alias}($val)
116 elsif (lc($_) eq lc($alias))
122 next if $new eq $_; # avoid (direct) recursion on bugs
123 my $enc = (ref($new)) ? $new : find_encoding($new);
139 my ($alias,$name) = splice(@_,0,2);
140 push(@alias, $alias => $name);
144 # Allow variants of iso-8859-1 etc.
145 define_alias( qr/^iso[-_]?(\d+)[-_](\d+)$/i => '"iso-$1-$2"' );
147 # At least HP-UX has these.
148 define_alias( qr/^iso8859(\d+)$/i => '"iso-8859-$1"' );
151 define_alias( qr/^(?:hp-)?(arabic|greek|hebrew|kana|roman|thai|turkish)8$/i => '"${1}8"' );
153 # The Official name of ASCII.
154 define_alias( qr/^ANSI[-_]?X3\.4[-_]?1968$/i => '"ascii"' );
156 # This is a font issue, not an encoding issue.
157 # (The currency symbol of the Latin 1 upper half
158 # has been redefined as the euro symbol.)
159 define_alias( qr/^(.+)\@euro$/i => '"$1"' );
161 # Allow latin-1 style names as well
162 define_alias( qr/^(?:iso[-_]?)?latin[-_]?(\d+)$/i => '"iso-8859-$latin2iso_num[$1]"' );
164 # Allow winlatin1 style names as well
165 define_alias( qr/^win(latin[12]|cyrillic|baltic|greek|turkish|hebrew|arabic|baltic|vietnamese)$/i => '"cp$winlatin2cp{\u$1}"' );
167 # Common names for non-latin prefered MIME names
168 define_alias( 'ascii' => 'US-ascii',
169 'cyrillic' => 'iso-8859-5',
170 'arabic' => 'iso-8859-6',
171 'greek' => 'iso-8859-7',
172 'hebrew' => 'iso-8859-8',
173 'thai' => 'iso-8859-11',
174 'tis620' => 'iso-8859-11',
177 # At least AIX has IBM-NNN (surprisingly...) instead of cpNNN.
178 # And Microsoft has their own naming (again, surprisingly).
179 define_alias( qr/^(?:ibm|ms)[-_]?(\d\d\d\d?)$/i => '"cp$1"');
181 # Sometimes seen with a leading zero.
182 define_alias( qr/^cp037$/i => '"cp37"');
185 define_alias( qr/^macRomanian$/i => '"macRumanian"');
187 # Standardize on the dashed versions.
188 define_alias( qr/^utf8$/i => 'utf-8' );
189 define_alias( qr/^koi8r$/i => 'koi8-r' );
190 define_alias( qr/^koi8u$/i => 'koi8-u' );
192 # Seen in some Linuxes.
193 define_alias( qr/^ujis$/i => 'euc-jp' );
195 # CP936 doesn't have vendor-addon for GBK, so they're identical.
196 define_alias( qr/^gbk$/i => '"cp936"');
198 # TODO: HP-UX '8' encodings arabic8 greek8 hebrew8 kana8 thai8 turkish8
199 # TODO: HP-UX '15' encodings japanese15 korean15 roi15
200 # TODO: Cyrillic encoding ISO-IR-111 (useful?)
201 # TODO: Armenian encoding ARMSCII-8
202 # TODO: Hebrew encoding ISO-8859-8-1
203 # TODO: Thai encoding TCVN
204 # TODO: Korean encoding Johab
205 # TODO: Vietnamese encodings VPS
206 # TODO: Japanese encoding JIS (not the same as SJIS)
207 # TODO: Mac Asian+African encodings: Arabic Armenian Bengali Burmese
208 # ChineseSimp ChineseTrad Devanagari Ethiopic ExtArabic
209 # Farsi Georgian Gujarati Gurmukhi Hebrew Japanese
210 # Kannada Khmer Korean Laotian Malayalam Mongolian
211 # Oriya Sinhalese Symbol Tamil Telugu Tibetan Vietnamese
213 # Map white space and _ to '-'
214 define_alias( qr/^(\S+)[\s_]+(.*)$/i => '"$1-$2"' );
220 $encoding{$name} = $obj;
222 define_alias($lc => $obj) unless $lc eq $name;
226 define_alias($alias,$obj);
233 my ($class,$name,$skip_external) = @_;
235 if (ref($name) && $name->can('new_sequence'))
240 if (exists $encoding{$name})
242 return $encoding{$name};
244 if (exists $encoding{$lc})
246 return $encoding{$lc};
249 my $oc = $class->findAlias($name);
250 return $oc if defined $oc;
252 $oc = $class->findAlias($lc) if $lc ne $name;
253 return $oc if defined $oc;
255 if (!$skip_external and exists $external_tables{$lc})
257 require $external_tables{$lc};
258 return $encoding{$name} if exists $encoding{$name};
266 my ($name,$skip_external) = @_;
267 return __PACKAGE__->getEncoding($name,$skip_external);
272 my ($name,$string,$check) = @_;
273 my $enc = find_encoding($name);
274 croak("Unknown encoding '$name'") unless defined $enc;
275 my $octets = $enc->encode($string,$check);
276 return undef if ($check && length($string));
282 my ($name,$octets,$check) = @_;
283 my $enc = find_encoding($name);
284 croak("Unknown encoding '$name'") unless defined $enc;
285 my $string = $enc->decode($octets,$check);
286 $_[1] = $octets if $check;
292 my ($string,$from,$to,$check) = @_;
293 my $f = find_encoding($from);
294 croak("Unknown encoding '$from'") unless defined $f;
295 my $t = find_encoding($to);
296 croak("Unknown encoding '$to'") unless defined $t;
297 my $uni = $f->decode($string,$check);
298 return undef if ($check && length($string));
299 $string = $t->encode($uni,$check);
300 return undef if ($check && length($uni));
301 return length($_[0] = $string);
314 return undef unless utf8::decode($str);
318 require Encode::Encoding;
320 require Encode::Internal;
321 require Encode::Unicode;
322 require Encode::utf8;
323 require Encode::iso10646_1;
324 require Encode::ucs2_le;
332 Encode - character encodings
340 The C<Encode> module provides the interfaces between Perl's strings
341 and the rest of the system. Perl strings are sequences of B<characters>.
343 The repertoire of characters that Perl can represent is at least that
344 defined by the Unicode Consortium. On most platforms the ordinal
345 values of the characters (as returned by C<ord(ch)>) is the "Unicode
346 codepoint" for the character (the exceptions are those platforms where
347 the legacy encoding is some variant of EBCDIC rather than a super-set
348 of ASCII - see L<perlebcdic>).
350 Traditionaly computer data has been moved around in 8-bit chunks
351 often called "bytes". These chunks are also known as "octets" in
352 networking standards. Perl is widely used to manipulate data of
353 many types - not only strings of characters representing human or
354 computer languages but also "binary" data being the machines representation
355 of numbers, pixels in an image - or just about anything.
357 When Perl is processing "binary data" the programmer wants Perl to process
358 "sequences of bytes". This is not a problem for Perl - as a byte has 256
359 possible values it easily fits in Perl's much larger "logical character".
361 Due to size concerns, each of B<CJK> (Chinese, Japanese & Korean) modules
362 are not loaded in memory until the first time they're used. Although you
363 don't have to C<use> the corresponding B<Encode::>(B<TW>|B<CN>|B<JP>|B<KR>)
364 modules first, be aware that those encodings will not be in C<%encodings>
365 until their module is loaded (either implicitly through using encodings
366 contained in the same module, or via an explicit C<use>).
374 I<character>: a character in the range 0..(2**32-1) (or more).
375 (What Perl's strings are made of.)
379 I<byte>: a character in the range 0..255
380 (A special case of a Perl character.)
384 I<octet>: 8 bits of data, with ordinal values 0..255
385 (Term for bytes passed to or from a non-Perl context, e.g. disk file.)
389 The marker [INTERNAL] marks Internal Implementation Details, in
390 general meant only for those who think they know what they are doing,
391 and such details may change in future releases.
395 =head2 Characteristics of an Encoding
397 An encoding has a "repertoire" of characters that it can represent,
398 and for each representable character there is at least one sequence of
399 octets that represents it.
401 =head2 Types of Encodings
403 Encodings can be divided into the following types:
407 =item * Fixed length 8-bit (or less) encodings.
409 Each character is a single octet so may have a repertoire of up to
410 256 characters. ASCII and iso-8859-* are typical examples.
412 =item * Fixed length 16-bit encodings
414 Each character is two octets so may have a repertoire of up to
415 65 536 characters. Unicode's UCS-2 is an example. Also used for
416 encodings for East Asian languages.
418 =item * Fixed length 32-bit encodings.
420 Not really very "encoded" encodings. The Unicode code points
421 are just represented as 4-octet integers. None the less because
422 different architectures use different representations of integers
423 (so called "endian") there at least two disctinct encodings.
425 =item * Multi-byte encodings
427 The number of octets needed to represent a character varies.
428 UTF-8 is a particularly complex but regular case of a multi-byte
429 encoding. Several East Asian countries use a multi-byte encoding
430 where 1-octet is used to cover western roman characters and Asian
431 characters get 2-octets.
432 (UTF-16 is strictly a multi-byte encoding taking either 2 or 4 octets
433 to represent a Unicode code point.)
435 =item * "Escape" encodings.
437 These encodings embed "escape sequences" into the octet sequence
438 which describe how the following octets are to be interpreted.
439 The iso-2022-* family is typical. Following the escape sequence
440 octets are encoded by an "embedded" encoding (which will be one
441 of the above types) until another escape sequence switches to
442 a different "embedded" encoding.
444 These schemes are very flexible and can handle mixed languages but are
445 very complex to process (and have state). No escape encodings are
446 implemented for Perl yet.
450 =head2 Specifying Encodings
452 Encodings can be specified to the API described below in two ways:
458 Encoding names are strings with characters taken from a restricted
459 repertoire. See L</"Encoding Names">.
461 =item 2. As an object
463 Encoding objects are returned by C<find_encoding($name, [$skip_external])>.
464 If the second parameter is true, Encode will refrain from loading external
465 modules for CJK encodings.
469 =head2 Encoding Names
471 Encoding names are case insensitive. White space in names is ignored.
472 In addition an encoding may have aliases. Each encoding has one
473 "canonical" name. The "canonical" name is chosen from the names of
474 the encoding by picking the first in the following sequence:
478 =item * The MIME name as defined in IETF RFCs.
480 =item * The name in the IANA registry.
482 =item * The name used by the organization that defined it.
486 Because of all the alias issues, and because in the general case
487 encodings have state C<Encode> uses the encoding object internally
488 once an operation is in progress.
490 As of Perl 5.8.0, at least the following encodings are recognized
491 (the => marks aliases):
505 The ISO 8859 and KOI:
507 ISO 8859-1 ISO 8859-6 ISO 8859-11 KOI8-F
508 ISO 8859-2 ISO 8859-7 (12 doesn't exist) KOI8-R
509 ISO 8859-3 ISO 8859-8 ISO 8859-13 KOI8-U
510 ISO 8859-4 ISO 8859-9 ISO 8859-14
511 ISO 8859-5 ISO 8859-10 ISO 8859-15
514 Latin1 => 8859-1 Latin6 => 8859-10
515 Latin2 => 8859-2 Latin7 => 8859-13
516 Latin3 => 8859-3 Latin8 => 8859-14
517 Latin4 => 8859-4 Latin9 => 8859-15
518 Latin5 => 8859-9 Latin10 => 8859-16
527 The CJKV: Chinese, Japanese, Korean, Vietnamese:
529 ISO 2022 ISO 2022 JP-1 JIS 0201 GB 1988 Big5 EUC-CN
530 ISO 2022 CN ISO 2022 JP-2 JIS 0208 GB 2312 HZ EUC-JP
531 ISO 2022 JP ISO 2022 KR JIS 0210 GB 12345 CNS 11643 EUC-JP-0212
532 Shift-JIS GBK Big5-HKSCS EUC-KR
535 (Due to size concerns, additional Chinese encodings including C<GB 18030>,
536 C<EUC-TW> and C<BIG5PLUS> are distributed separately on CPAN, under the name
537 L<Encode::HanExtra>.)
541 CP37 CP852 CP861 CP866 CP949 CP1251 CP1256
542 CP424 CP855 CP862 CP869 CP950 CP1252 CP1257
543 CP737 CP856 CP863 CP874 CP1006 CP1253 CP1258
544 CP775 CP857 CP864 CP932 CP1047 CP1254
545 CP850 CP860 CP865 CP936 CP1250 CP1255
549 WinCyrillic => CP1251
551 WinTurkiskh => CP1254
555 WinVietnamese => CP1258
557 (All the CPI<NNN...> are available also as IBMI<NNN...>.)
561 MacCentralEuropean MacJapanese
563 MacCyrillic MacRomanian
566 MacIcelandic MacTurkish
577 =head1 PERL ENCODING API
579 =head2 Generic Encoding Interface
585 $bytes = encode(ENCODING, $string[, CHECK])
587 Encodes string from Perl's internal form into I<ENCODING> and returns
588 a sequence of octets. For CHECK see L</"Handling Malformed Data">.
590 For example to convert (internally UTF-8 encoded) Unicode data
593 $octets = encode("utf8", $unicode);
597 $string = decode(ENCODING, $bytes[, CHECK])
599 Decode sequence of octets assumed to be in I<ENCODING> into Perl's
600 internal form and returns the resulting string. For CHECK see
601 L</"Handling Malformed Data">.
603 For example to convert ISO 8859-1 data to UTF-8:
605 $utf8 = decode("latin1", $latin1);
609 from_to($string, FROM_ENCODING, TO_ENCODING[, CHECK])
611 Convert B<in-place> the data between two encodings. How did the data
612 in $string originally get to be in FROM_ENCODING? Either using
613 encode() or through PerlIO: See L</"Encoding and IO">. For CHECK
614 see L</"Handling Malformed Data">.
616 For example to convert ISO 8859-1 data to UTF-8:
618 from_to($data, "iso-8859-1", "utf-8");
620 and to convert it back:
622 from_to($data, "utf-8", "iso-8859-1");
624 Note that because the conversion happens in place, the data to be
625 converted cannot be a string constant, it must be a scalar variable.
629 =head2 Handling Malformed Data
631 If CHECK is not set, C<undef> is returned. If the data is supposed to
632 be UTF-8, an optional lexical warning (category utf8) is given. If
633 CHECK is true but not a code reference, dies.
635 It would desirable to have a way to indicate that transform should use
636 the encodings "replacement character" - no such mechanism is defined yet.
638 It is also planned to allow I<CHECK> to be a code reference.
640 This is not yet implemented as there are design issues with what its
641 arguments should be and how it returns its results.
647 Passed remaining fragment of string being processed.
648 Modifies it in place to remove bytes/characters it can understand
649 and returns a string used to represent them.
653 my $ch = substr($_[0],0,1,'');
654 return sprintf("\x{%02X}",ord($ch);
657 This scheme is close to how underlying C code for Encode works, but gives
658 the fixup routine very little context.
662 Passed original string, and an index into it of the problem area, and
663 output string so far. Appends what it will to output string and
664 returns new index into original string. For example:
667 # my ($s,$i,$d) = @_;
668 my $ch = substr($_[0],$_[1],1);
669 $_[2] .= sprintf("\x{%02X}",ord($ch);
673 This scheme gives maximal control to the fixup routine but is more
674 complicated to code, and may need internals of Encode to be tweaked to
675 keep original string intact.
681 Multiple return values rather than in-place modifications.
683 Index into the string could be pos($str) allowing s/\G...//.
689 The Unicode consortium defines the UTF-8 standard as a way of encoding
690 the entire Unicode repertiore as sequences of octets. This encoding is
691 expected to become very widespread. Perl can use this form internaly
692 to represent strings, so conversions to and from this form are
693 particularly efficient (as octets in memory do not have to change,
694 just the meta-data that tells Perl how to treat them).
700 $bytes = encode_utf8($string);
702 The characters that comprise string are encoded in Perl's superset of UTF-8
703 and the resulting octets returned as a sequence of bytes. All possible
704 characters have a UTF-8 representation so this function cannot fail.
708 $string = decode_utf8($bytes [,CHECK]);
710 The sequence of octets represented by $bytes is decoded from UTF-8
711 into a sequence of logical characters. Not all sequences of octets
712 form valid UTF-8 encodings, so it is possible for this call to fail.
713 For CHECK see L</"Handling Malformed Data">.
717 =head2 Other Encodings of Unicode
719 UTF-16 is similar to UCS-2, 16 bit or 2-byte chunks. UCS-2 can only
720 represent 0..0xFFFF, while UTF-16 has a I<surrogate pair> scheme which
721 allows it to cover the whole Unicode range.
723 Surrogates are code points set aside to encode the 0x01000..0x10FFFF
724 range of Unicode code points in pairs of 16-bit units. The I<high
725 surrogates> are the range 0xD800..0xDBFF, and the I<low surrogates>
726 are the range 0xDC00..0xDFFFF. The surrogate encoding is
728 $hi = ($uni - 0x10000) / 0x400 + 0xD800;
729 $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
733 $uni = 0x10000 + ($hi - 0xD8000) * 0x400 + ($lo - 0xDC00);
735 Encode implements big-endian UCS-2 aliased to "iso-10646-1" as that
736 happens to be the name used by that representation when used with X11
739 UTF-32 or UCS-4 is 32-bit or 4-byte chunks. Perl's logical characters
740 can be considered as being in this form without encoding. An encoding
741 to transfer strings in this form (e.g. to write them to a file) would
744 pack('L*', unpack('U*', $string)); # native
746 pack('V*', unpack('U*', $string)); # little-endian
748 pack('N*', unpack('U*', $string)); # big-endian
750 depending on the endianness required.
752 No UTF-32 encodings are implemented yet.
754 Both UCS-2 and UCS-4 style encodings can have "byte order marks" by
755 representing the code point 0xFFFE as the very first thing in a file.
757 =head2 Listing available encodings
759 use Encode qw(encodings);
762 Returns a list of the canonical names of the available encodings.
764 =head2 Defining Aliases
766 use Encode qw(define_alias);
767 define_alias( newName => ENCODING);
769 Allows newName to be used as am alias for ENCODING. ENCODING may be
770 either the name of an encoding or and encoding object (as above).
772 Currently I<newName> can be specified in the following ways:
776 =item As a simple string.
778 =item As a qr// compiled regular expression, e.g.:
780 define_alias( qr/^iso8859-(\d+)$/i => '"iso-8859-$1"' );
782 In this case if I<ENCODING> is not a reference it is C<eval>-ed to
783 allow C<$1> etc. to be subsituted. The example is one way to names as
784 used in X11 font names to alias the MIME names for the iso-8859-*
787 =item As a code reference, e.g.:
789 define_alias( sub { return /^iso8859-(\d+)$/i ? "iso-8859-$1" : undef } , '');
791 In this case C<$_> will be set to the name that is being looked up and
792 I<ENCODING> is passed to the sub as its first argument. The example
793 is another way to names as used in X11 font names to alias the MIME
794 names for the iso-8859-* family.
798 =head2 Defining Encodings
800 use Encode qw(define_alias);
801 define_encoding( $object, 'canonicalName' [,alias...]);
803 Causes I<canonicalName> to be associated with I<$object>. The object
804 should provide the interface described in L</"IMPLEMENTATION CLASSES">
805 below. If more than two arguments are provided then additional
806 arguments are taken as aliases for I<$object> as for C<define_alias>.
808 =head1 Encoding and IO
810 It is very common to want to do encoding transformations when
811 reading or writing files, network connections, pipes etc.
812 If Perl is configured to use the new 'perlio' IO system then
813 C<Encode> provides a "layer" (See L<perliol>) which can transform
814 data as it is read or written.
816 Here is how the blind poet would modernise the encoding:
819 open(my $iliad,'<:encoding(iso-8859-7)','iliad.greek');
820 open(my $utf8,'>:utf8','iliad.utf8');
826 In addition the new IO system can also be configured to read/write
827 UTF-8 encoded characters (as noted above this is efficient):
829 open(my $fh,'>:utf8','anything');
830 print $fh "Any \x{0021} string \N{SMILEY FACE}\n";
832 Either of the above forms of "layer" specifications can be made the default
833 for a lexical scope with the C<use open ...> pragma. See L<open>.
835 Once a handle is open is layers can be altered using C<binmode>.
837 Without any such configuration, or if Perl itself is built using
838 system's own IO, then write operations assume that file handle accepts
839 only I<bytes> and will C<die> if a character larger than 255 is
840 written to the handle. When reading, each octet from the handle
841 becomes a byte-in-a-character. Note that this default is the same
842 behaviour as bytes-only languages (including Perl before v5.6) would
843 have, and is sufficient to handle native 8-bit encodings
844 e.g. iso-8859-1, EBCDIC etc. and any legacy mechanisms for handling
845 other encodings and binary data.
847 In other cases it is the programs responsibility to transform
848 characters into bytes using the API above before doing writes, and to
849 transform the bytes read from a handle into characters before doing
850 "character operations" (e.g. C<lc>, C</\W+/>, ...).
852 You can also use PerlIO to convert larger amounts of data you don't
853 want to bring into memory. For example to convert between ISO 8859-1
854 (Latin 1) and UTF-8 (or UTF-EBCDIC in EBCDIC machines):
856 open(F, "<:encoding(iso-8859-1)", "data.txt") or die $!;
857 open(G, ">:utf8", "data.utf") or die $!;
858 while (<F>) { print G }
860 # Could also do "print G <F>" but that would pull
861 # the whole file into memory just to write it out again.
865 open(my $f, "<:encoding(cp1252)")
866 open(my $g, ">:encoding(iso-8859-2)")
867 open(my $h, ">:encoding(latin9)") # iso-8859-15
869 See L<PerlIO> for more information.
871 See also L<encoding> for how to change the default encoding of the
874 =head1 Encoding How to ...
880 =item * IO with mixed content (faking iso-2020-*)
882 =item * MIME's Content-Length:
884 =item * UTF-8 strings in binary data.
886 =item * Perl/Encode wrappers on non-Unicode XS modules.
890 =head1 Messing with Perl's Internals
892 The following API uses parts of Perl's internals in the current
893 implementation. As such they are efficient, but may change.
897 =item * is_utf8(STRING [, CHECK])
899 [INTERNAL] Test whether the UTF-8 flag is turned on in the STRING.
900 If CHECK is true, also checks the data in STRING for being well-formed
901 UTF-8. Returns true if successful, false otherwise.
903 =item * valid_utf8(STRING)
905 [INTERNAL] Test whether STRING is in a consistent state. Will return
906 true if string is held as bytes, or is well-formed UTF-8 and has the
907 UTF-8 flag on. Main reason for this routine is to allow Perl's
908 testsuite to check that operations have left strings in a consistent
915 [INTERNAL] Turn on the UTF-8 flag in STRING. The data in STRING is
916 B<not> checked for being well-formed UTF-8. Do not use unless you
917 B<know> that the STRING is well-formed UTF-8. Returns the previous
918 state of the UTF-8 flag (so please don't test the return value as
919 I<not> success or failure), or C<undef> if STRING is not a string.
925 [INTERNAL] Turn off the UTF-8 flag in STRING. Do not use frivolously.
926 Returns the previous state of the UTF-8 flag (so please don't test the
927 return value as I<not> success or failure), or C<undef> if STRING is
932 =head1 IMPLEMENTATION CLASSES
934 As mentioned above encodings are (in the current implementation at least)
935 defined by objects. The mapping of encoding name to object is via the
938 The values of the hash can currently be either strings or objects.
939 The string form may go away in the future. The string form occurs
940 when C<encodings()> has scanned C<@INC> for loadable encodings but has
941 not actually loaded the encoding in question. This is because the
942 current "loading" process is all Perl and a bit slow.
944 Once an encoding is loaded then value of the hash is object which
945 implements the encoding. The object should provide the following
952 Should return the string representing the canonical name of the encoding.
954 =item -E<gt>new_sequence
956 This is a placeholder for encodings with state. It should return an
957 object which implements this interface, all current implementations
958 return the original object.
960 =item -E<gt>encode($string,$check)
962 Should return the octet sequence representing I<$string>. If I<$check>
963 is true it should modify I<$string> in place to remove the converted
964 part (i.e. the whole string unless there is an error). If an error
965 occurs it should return the octet sequence for the fragment of string
966 that has been converted, and modify $string in-place to remove the
967 converted part leaving it starting with the problem fragment.
969 If check is is false then C<encode> should make a "best effort" to
970 convert the string - for example by using a replacement character.
972 =item -E<gt>decode($octets,$check)
974 Should return the string that I<$octets> represents. If I<$check> is
975 true it should modify I<$octets> in place to remove the converted part
976 (i.e. the whole sequence unless there is an error). If an error
977 occurs it should return the fragment of string that has been
978 converted, and modify $octets in-place to remove the converted part
979 leaving it starting with the problem fragment.
981 If check is is false then C<decode> should make a "best effort" to
982 convert the string - for example by using Unicode's "\x{FFFD}" as a
983 replacement character.
987 It should be noted that the check behaviour is different from the
988 outer public API. The logic is that the "unchecked" case is useful
989 when encoding is part of a stream which may be reporting errors
990 (e.g. STDERR). In such cases it is desirable to get everything
991 through somehow without causing additional errors which obscure the
992 original one. Also the encoding is best placed to know what the
993 correct replacement character is, so if that is the desired behaviour
994 then letting low level code do it is the most efficient.
996 In contrast if check is true, the scheme above allows the encoding to
997 do as much as it can and tell layer above how much that was. What is
998 lacking at present is a mechanism to report what went wrong. The most
999 likely interface will be an additional method call to the object, or
1000 perhaps (to avoid forcing per-stream objects on otherwise stateless
1001 encodings) and additional parameter.
1003 It is also highly desirable that encoding classes inherit from
1004 C<Encode::Encoding> as a base class. This allows that class to define
1005 additional behaviour for all encoding objects. For example built in
1006 Unicode, UCS-2 and UTF-8 classes use :
1008 package Encode::MyEncoding;
1009 use base qw(Encode::Encoding);
1011 __PACKAGE__->Define(qw(myCanonical myAlias));
1013 To create an object with bless {Name => ...},$class, and call
1014 define_encoding. They inherit their C<name> method from
1015 C<Encode::Encoding>.
1017 =head2 Compiled Encodings
1019 F<Encode.xs> provides a class C<Encode::XS> which provides the
1020 interface described above. It calls a generic octet-sequence to
1021 octet-sequence "engine" that is driven by tables (defined in
1022 F<encengine.c>). The same engine is used for both encode and
1023 decode. C<Encode:XS>'s C<encode> forces Perl's characters to their
1024 UTF-8 form and then treats them as just another multibyte
1025 encoding. C<Encode:XS>'s C<decode> transforms the sequence and then
1026 turns the UTF-8-ness flag as that is the form that the tables are
1027 defined to produce. For details of the engine see the comments in
1030 The tables are produced by the Perl script F<compile> (the name needs
1031 to change so we can eventually install it somewhere). F<compile> can
1032 currently read two formats:
1038 This is a coined format used by Tcl. It is documented in
1039 Encode/EncodeFormat.pod.
1043 This is the semi-standard format used by IBM's ICU package.
1047 F<compile> can write the following forms:
1053 See above - the F<Encode/*.ucm> files provided with the distribution have
1054 been created from the original Tcl .enc files using this approach.
1058 Produces tables as C data structures - this is used to build in encodings
1059 into F<Encode.so>/F<Encode.dll>.
1063 In theory this allows encodings to be stand-alone loadable Perl
1064 extensions. The process has not yet been tested. The plan is to use
1065 this approach for large East Asian encodings.
1069 The set of encodings built-in to F<Encode.so>/F<Encode.dll> is
1070 determined by F<Makefile.PL>. The current set is as follows:
1074 =item ascii and iso-8859-*
1076 That is all the common 8-bit "western" encodings.
1078 =item IBM-1047 and two other variants of EBCDIC.
1080 These are the same variants that are supported by EBCDIC Perl as
1081 "native" encodings. They are included to prove "reversibility" of
1082 some constructs in EBCDIC Perl.
1084 =item symbol and dingbats as used by Tk on X11.
1086 (The reason Encode got started was to support Perl/Tk.)
1090 That set is rather ad hoc and has been driven by the needs of the
1091 tests rather than the needs of typical applications. It is likely
1096 L<perlunicode>, L<perlebcdic>, L<perlfunc/open>, L<PerlIO>, L<encoding>