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 shiftjis => 'Encode/JP.pm',
70 macjapan => 'Encode/JP.pm',
71 cp932 => 'Encode/JP.pm',
72 'euc-kr' => 'Encode/KR.pm',
73 ksc5601 => 'Encode/KR.pm',
74 cp949 => 'Encode/KR.pm',
75 big5 => 'Encode/TW.pm',
76 'big5-hkscs' => 'Encode/TW.pm',
77 cp950 => 'Encode/TW.pm',
78 gb18030 => 'Encode/HanExtra.pm',
79 big5plus => 'Encode/HanExtra.pm',
80 'euc-tw' => 'Encode/HanExtra.pm',
88 sort { $a->[1] cmp $b->[1] }
90 grep { $_ ne 'Internal' }
98 # print "# findAlias $_\n";
99 unless (exists $alias{$_})
101 for (my $i=0; $i < @alias; $i += 2)
103 my $alias = $alias[$i];
104 my $val = $alias[$i+1];
106 if (ref($alias) eq 'Regexp' && $_ =~ $alias)
110 elsif (ref($alias) eq 'CODE')
112 $new = &{$alias}($val)
114 elsif (lc($_) eq lc($alias))
120 next if $new eq $_; # avoid (direct) recursion on bugs
121 my $enc = (ref($new)) ? $new : find_encoding($new);
137 my ($alias,$name) = splice(@_,0,2);
138 push(@alias, $alias => $name);
142 # Allow variants of iso-8859-1 etc.
143 define_alias( qr/^iso[-_]?(\d+)[-_](\d+)$/i => '"iso-$1-$2"' );
145 # At least HP-UX has these.
146 define_alias( qr/^iso8859(\d+)$/i => '"iso-8859-$1"' );
149 define_alias( qr/^(?:hp-)?(arabic|greek|hebrew|kana|roman|thai|turkish)8$/i => '"${1}8"' );
151 # The Official name of ASCII.
152 define_alias( qr/^ANSI[-_]?X3\.4[-_]?1968$/i => '"ascii"' );
154 # This is a font issue, not an encoding issue.
155 # (The currency symbol of the Latin 1 upper half
156 # has been redefined as the euro symbol.)
157 define_alias( qr/^(.+)\@euro$/i => '"$1"' );
159 # Allow latin-1 style names as well
160 define_alias( qr/^(?:iso[-_]?)?latin[-_]?(\d+)$/i => '"iso-8859-$latin2iso_num[$1]"' );
162 # Allow winlatin1 style names as well
163 define_alias( qr/^win(latin[12]|cyrillic|baltic|greek|turkish|hebrew|arabic|baltic|vietnamese)$/i => '"cp$winlatin2cp{\u$1}"' );
165 # Common names for non-latin prefered MIME names
166 define_alias( 'ascii' => 'US-ascii',
167 'cyrillic' => 'iso-8859-5',
168 'arabic' => 'iso-8859-6',
169 'greek' => 'iso-8859-7',
170 'hebrew' => 'iso-8859-8',
171 'thai' => 'iso-8859-11',
172 'tis620' => 'iso-8859-11',
175 # At least AIX has IBM-NNN (surprisingly...) instead of cpNNN.
176 # And Microsoft has their own naming (again, surprisingly).
177 define_alias( qr/^(?:ibm|ms)[-_]?(\d\d\d\d?)$/i => '"cp$1"');
179 # Sometimes seen with a leading zero.
180 define_alias( qr/^cp037$/i => '"cp37"');
183 define_alias( qr/^macRomanian$/i => '"macRumanian"');
185 # Standardize on the dashed versions.
186 define_alias( qr/^utf8$/i => 'utf-8' );
187 define_alias( qr/^koi8r$/i => 'koi8-r' );
188 define_alias( qr/^koi8u$/i => 'koi8-u' );
190 # Seen in some Linuxes.
191 define_alias( qr/^ujis$/i => 'euc-jp' );
193 # CP936 doesn't have vendor-addon for GBK, so they're identical.
194 define_alias( qr/^gbk$/i => '"cp936"');
196 # TODO: HP-UX '8' encodings arabic8 greek8 hebrew8 kana8 thai8 turkish8
197 # TODO: HP-UX '15' encodings japanese15 korean15 roi15
198 # TODO: Cyrillic encoding ISO-IR-111 (useful?)
199 # TODO: Armenian encoding ARMSCII-8
200 # TODO: Hebrew encoding ISO-8859-8-1
201 # TODO: Thai encoding TCVN
202 # TODO: Korean encoding Johab
203 # TODO: Vietnamese encodings VPS
204 # TODO: Japanese encoding JIS (not the same as SJIS)
205 # TODO: Mac Asian+African encodings: Arabic Armenian Bengali Burmese
206 # ChineseSimp ChineseTrad Devanagari Ethiopic ExtArabic
207 # Farsi Georgian Gujarati Gurmukhi Hebrew Japanese
208 # Kannada Khmer Korean Laotian Malayalam Mongolian
209 # Oriya Sinhalese Symbol Tamil Telugu Tibetan Vietnamese
211 # Map white space and _ to '-'
212 define_alias( qr/^(\S+)[\s_]+(.*)$/i => '"$1-$2"' );
218 $encoding{$name} = $obj;
220 define_alias($lc => $obj) unless $lc eq $name;
224 define_alias($alias,$obj);
231 my ($class,$name,$skip_external) = @_;
233 if (ref($name) && $name->can('new_sequence'))
238 if (exists $encoding{$name})
240 return $encoding{$name};
242 if (exists $encoding{$lc})
244 return $encoding{$lc};
247 my $oc = $class->findAlias($name);
248 return $oc if defined $oc;
250 $oc = $class->findAlias($lc) if $lc ne $name;
251 return $oc if defined $oc;
253 if (!$skip_external and exists $external_tables{$lc})
255 require $external_tables{$lc};
256 return $encoding{$name} if exists $encoding{$name};
264 my ($name,$skip_external) = @_;
265 return __PACKAGE__->getEncoding($name,$skip_external);
270 my ($name,$string,$check) = @_;
271 my $enc = find_encoding($name);
272 croak("Unknown encoding '$name'") unless defined $enc;
273 my $octets = $enc->encode($string,$check);
274 return undef if ($check && length($string));
280 my ($name,$octets,$check) = @_;
281 my $enc = find_encoding($name);
282 croak("Unknown encoding '$name'") unless defined $enc;
283 my $string = $enc->decode($octets,$check);
284 $_[1] = $octets if $check;
290 my ($string,$from,$to,$check) = @_;
291 my $f = find_encoding($from);
292 croak("Unknown encoding '$from'") unless defined $f;
293 my $t = find_encoding($to);
294 croak("Unknown encoding '$to'") unless defined $t;
295 my $uni = $f->decode($string,$check);
296 return undef if ($check && length($string));
297 $string = $t->encode($uni,$check);
298 return undef if ($check && length($uni));
299 return length($_[0] = $string);
312 return undef unless utf8::decode($str);
316 require Encode::Encoding;
318 require Encode::Internal;
319 require Encode::Unicode;
320 require Encode::utf8;
321 require Encode::iso10646_1;
322 require Encode::ucs2_le;
330 Encode - character encodings
338 The C<Encode> module provides the interfaces between Perl's strings
339 and the rest of the system. Perl strings are sequences of B<characters>.
341 The repertoire of characters that Perl can represent is at least that
342 defined by the Unicode Consortium. On most platforms the ordinal
343 values of the characters (as returned by C<ord(ch)>) is the "Unicode
344 codepoint" for the character (the exceptions are those platforms where
345 the legacy encoding is some variant of EBCDIC rather than a super-set
346 of ASCII - see L<perlebcdic>).
348 Traditionaly computer data has been moved around in 8-bit chunks
349 often called "bytes". These chunks are also known as "octets" in
350 networking standards. Perl is widely used to manipulate data of
351 many types - not only strings of characters representing human or
352 computer languages but also "binary" data being the machines representation
353 of numbers, pixels in an image - or just about anything.
355 When Perl is processing "binary data" the programmer wants Perl to process
356 "sequences of bytes". This is not a problem for Perl - as a byte has 256
357 possible values it easily fits in Perl's much larger "logical character".
359 Due to size concerns, each of B<CJK> (Chinese, Japanese & Korean) modules
360 are not loaded in memory until the first time they're used. Although you
361 don't have to C<use> the corresponding B<Encode::>(B<TW>|B<CN>|B<JP>|B<KR>)
362 modules first, be aware that those encodings will not be in C<%encodings>
363 until their module is loaded (either implicitly through using encodings
364 contained in the same module, or via an explicit C<use>).
372 I<character>: a character in the range 0..(2**32-1) (or more).
373 (What Perl's strings are made of.)
377 I<byte>: a character in the range 0..255
378 (A special case of a Perl character.)
382 I<octet>: 8 bits of data, with ordinal values 0..255
383 (Term for bytes passed to or from a non-Perl context, e.g. disk file.)
387 The marker [INTERNAL] marks Internal Implementation Details, in
388 general meant only for those who think they know what they are doing,
389 and such details may change in future releases.
393 =head2 Characteristics of an Encoding
395 An encoding has a "repertoire" of characters that it can represent,
396 and for each representable character there is at least one sequence of
397 octets that represents it.
399 =head2 Types of Encodings
401 Encodings can be divided into the following types:
405 =item * Fixed length 8-bit (or less) encodings.
407 Each character is a single octet so may have a repertoire of up to
408 256 characters. ASCII and iso-8859-* are typical examples.
410 =item * Fixed length 16-bit encodings
412 Each character is two octets so may have a repertoire of up to
413 65 536 characters. Unicode's UCS-2 is an example. Also used for
414 encodings for East Asian languages.
416 =item * Fixed length 32-bit encodings.
418 Not really very "encoded" encodings. The Unicode code points
419 are just represented as 4-octet integers. None the less because
420 different architectures use different representations of integers
421 (so called "endian") there at least two disctinct encodings.
423 =item * Multi-byte encodings
425 The number of octets needed to represent a character varies.
426 UTF-8 is a particularly complex but regular case of a multi-byte
427 encoding. Several East Asian countries use a multi-byte encoding
428 where 1-octet is used to cover western roman characters and Asian
429 characters get 2-octets.
430 (UTF-16 is strictly a multi-byte encoding taking either 2 or 4 octets
431 to represent a Unicode code point.)
433 =item * "Escape" encodings.
435 These encodings embed "escape sequences" into the octet sequence
436 which describe how the following octets are to be interpreted.
437 The iso-2022-* family is typical. Following the escape sequence
438 octets are encoded by an "embedded" encoding (which will be one
439 of the above types) until another escape sequence switches to
440 a different "embedded" encoding.
442 These schemes are very flexible and can handle mixed languages but are
443 very complex to process (and have state). No escape encodings are
444 implemented for Perl yet.
448 =head2 Specifying Encodings
450 Encodings can be specified to the API described below in two ways:
456 Encoding names are strings with characters taken from a restricted
457 repertoire. See L</"Encoding Names">.
459 =item 2. As an object
461 Encoding objects are returned by C<find_encoding($name, [$skip_external])>.
462 If the second parameter is true, Encode will refrain from loading external
463 modules for CJK encodings.
467 =head2 Encoding Names
469 Encoding names are case insensitive. White space in names is ignored.
470 In addition an encoding may have aliases. Each encoding has one
471 "canonical" name. The "canonical" name is chosen from the names of
472 the encoding by picking the first in the following sequence:
476 =item * The MIME name as defined in IETF RFCs.
478 =item * The name in the IANA registry.
480 =item * The name used by the organization that defined it.
484 Because of all the alias issues, and because in the general case
485 encodings have state C<Encode> uses the encoding object internally
486 once an operation is in progress.
488 As of Perl 5.8.0, at least the following encodings are recognized
489 (the => marks aliases):
503 The ISO 8859 and KOI:
505 ISO 8859-1 ISO 8859-6 ISO 8859-11 KOI8-F
506 ISO 8859-2 ISO 8859-7 (12 doesn't exist) KOI8-R
507 ISO 8859-3 ISO 8859-8 ISO 8859-13 KOI8-U
508 ISO 8859-4 ISO 8859-9 ISO 8859-14
509 ISO 8859-5 ISO 8859-10 ISO 8859-15
512 Latin1 => 8859-1 Latin6 => 8859-10
513 Latin2 => 8859-2 Latin7 => 8859-13
514 Latin3 => 8859-3 Latin8 => 8859-14
515 Latin4 => 8859-4 Latin9 => 8859-15
516 Latin5 => 8859-9 Latin10 => 8859-16
525 The CJKV: Chinese, Japanese, Korean, Vietnamese:
527 ISO 2022 ISO 2022 JP-1 JIS 0201 GB 1988 Big5 EUC-CN
528 ISO 2022 CN ISO 2022 JP-2 JIS 0208 GB 2312 HZ EUC-JP
529 ISO 2022 JP ISO 2022 KR JIS 0210 GB 12345 CNS 11643 EUC-JP-0212
530 Shift-JIS GBK Big5-HKSCS EUC-KR
533 (Due to size concerns, additional Chinese encodings including C<GB 18030>,
534 C<EUC-TW> and C<BIG5PLUS> are distributed separately on CPAN, under the name
535 L<Encode::HanExtra>.)
539 CP37 CP852 CP861 CP866 CP949 CP1251 CP1256
540 CP424 CP855 CP862 CP869 CP950 CP1252 CP1257
541 CP737 CP856 CP863 CP874 CP1006 CP1253 CP1258
542 CP775 CP857 CP864 CP932 CP1047 CP1254
543 CP850 CP860 CP865 CP936 CP1250 CP1255
547 WinCyrillic => CP1251
549 WinTurkiskh => CP1254
553 WinVietnamese => CP1258
555 (All the CPI<NNN...> are available also as IBMI<NNN...>.)
559 MacCentralEuropean MacJapanese
561 MacCyrillic MacRomanian
564 MacIcelandic MacTurkish
575 =head1 PERL ENCODING API
577 =head2 Generic Encoding Interface
583 $bytes = encode(ENCODING, $string[, CHECK])
585 Encodes string from Perl's internal form into I<ENCODING> and returns
586 a sequence of octets. For CHECK see L</"Handling Malformed Data">.
588 For example to convert (internally UTF-8 encoded) Unicode data
591 $octets = encode("utf8", $unicode);
595 $string = decode(ENCODING, $bytes[, CHECK])
597 Decode sequence of octets assumed to be in I<ENCODING> into Perl's
598 internal form and returns the resulting string. For CHECK see
599 L</"Handling Malformed Data">.
601 For example to convert ISO 8859-1 data to UTF-8:
603 $utf8 = decode("latin1", $latin1);
607 from_to($string, FROM_ENCODING, TO_ENCODING[, CHECK])
609 Convert B<in-place> the data between two encodings. How did the data
610 in $string originally get to be in FROM_ENCODING? Either using
611 encode() or through PerlIO: See L</"Encoding and IO">. For CHECK
612 see L</"Handling Malformed Data">.
614 For example to convert ISO 8859-1 data to UTF-8:
616 from_to($data, "iso-8859-1", "utf-8");
618 and to convert it back:
620 from_to($data, "utf-8", "iso-8859-1");
622 Note that because the conversion happens in place, the data to be
623 converted cannot be a string constant, it must be a scalar variable.
627 =head2 Handling Malformed Data
629 If CHECK is not set, C<undef> is returned. If the data is supposed to
630 be UTF-8, an optional lexical warning (category utf8) is given. If
631 CHECK is true but not a code reference, dies.
633 It would desirable to have a way to indicate that transform should use
634 the encodings "replacement character" - no such mechanism is defined yet.
636 It is also planned to allow I<CHECK> to be a code reference.
638 This is not yet implemented as there are design issues with what its
639 arguments should be and how it returns its results.
645 Passed remaining fragment of string being processed.
646 Modifies it in place to remove bytes/characters it can understand
647 and returns a string used to represent them.
651 my $ch = substr($_[0],0,1,'');
652 return sprintf("\x{%02X}",ord($ch);
655 This scheme is close to how underlying C code for Encode works, but gives
656 the fixup routine very little context.
660 Passed original string, and an index into it of the problem area, and
661 output string so far. Appends what it will to output string and
662 returns new index into original string. For example:
665 # my ($s,$i,$d) = @_;
666 my $ch = substr($_[0],$_[1],1);
667 $_[2] .= sprintf("\x{%02X}",ord($ch);
671 This scheme gives maximal control to the fixup routine but is more
672 complicated to code, and may need internals of Encode to be tweaked to
673 keep original string intact.
679 Multiple return values rather than in-place modifications.
681 Index into the string could be pos($str) allowing s/\G...//.
687 The Unicode consortium defines the UTF-8 standard as a way of encoding
688 the entire Unicode repertiore as sequences of octets. This encoding is
689 expected to become very widespread. Perl can use this form internaly
690 to represent strings, so conversions to and from this form are
691 particularly efficient (as octets in memory do not have to change,
692 just the meta-data that tells Perl how to treat them).
698 $bytes = encode_utf8($string);
700 The characters that comprise string are encoded in Perl's superset of UTF-8
701 and the resulting octets returned as a sequence of bytes. All possible
702 characters have a UTF-8 representation so this function cannot fail.
706 $string = decode_utf8($bytes [,CHECK]);
708 The sequence of octets represented by $bytes is decoded from UTF-8
709 into a sequence of logical characters. Not all sequences of octets
710 form valid UTF-8 encodings, so it is possible for this call to fail.
711 For CHECK see L</"Handling Malformed Data">.
715 =head2 Other Encodings of Unicode
717 UTF-16 is similar to UCS-2, 16 bit or 2-byte chunks. UCS-2 can only
718 represent 0..0xFFFF, while UTF-16 has a I<surrogate pair> scheme which
719 allows it to cover the whole Unicode range.
721 Surrogates are code points set aside to encode the 0x01000..0x10FFFF
722 range of Unicode code points in pairs of 16-bit units. The I<high
723 surrogates> are the range 0xD800..0xDBFF, and the I<low surrogates>
724 are the range 0xDC00..0xDFFFF. The surrogate encoding is
726 $hi = ($uni - 0x10000) / 0x400 + 0xD800;
727 $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
731 $uni = 0x10000 + ($hi - 0xD8000) * 0x400 + ($lo - 0xDC00);
733 Encode implements big-endian UCS-2 aliased to "iso-10646-1" as that
734 happens to be the name used by that representation when used with X11
737 UTF-32 or UCS-4 is 32-bit or 4-byte chunks. Perl's logical characters
738 can be considered as being in this form without encoding. An encoding
739 to transfer strings in this form (e.g. to write them to a file) would
742 pack('L*', unpack('U*', $string)); # native
744 pack('V*', unpack('U*', $string)); # little-endian
746 pack('N*', unpack('U*', $string)); # big-endian
748 depending on the endianness required.
750 No UTF-32 encodings are implemented yet.
752 Both UCS-2 and UCS-4 style encodings can have "byte order marks" by
753 representing the code point 0xFFFE as the very first thing in a file.
755 =head2 Listing available encodings
757 use Encode qw(encodings);
760 Returns a list of the canonical names of the available encodings.
762 =head2 Defining Aliases
764 use Encode qw(define_alias);
765 define_alias( newName => ENCODING);
767 Allows newName to be used as am alias for ENCODING. ENCODING may be
768 either the name of an encoding or and encoding object (as above).
770 Currently I<newName> can be specified in the following ways:
774 =item As a simple string.
776 =item As a qr// compiled regular expression, e.g.:
778 define_alias( qr/^iso8859-(\d+)$/i => '"iso-8859-$1"' );
780 In this case if I<ENCODING> is not a reference it is C<eval>-ed to
781 allow C<$1> etc. to be subsituted. The example is one way to names as
782 used in X11 font names to alias the MIME names for the iso-8859-*
785 =item As a code reference, e.g.:
787 define_alias( sub { return /^iso8859-(\d+)$/i ? "iso-8859-$1" : undef } , '');
789 In this case C<$_> will be set to the name that is being looked up and
790 I<ENCODING> is passed to the sub as its first argument. The example
791 is another way to names as used in X11 font names to alias the MIME
792 names for the iso-8859-* family.
796 =head2 Defining Encodings
798 use Encode qw(define_alias);
799 define_encoding( $object, 'canonicalName' [,alias...]);
801 Causes I<canonicalName> to be associated with I<$object>. The object
802 should provide the interface described in L</"IMPLEMENTATION CLASSES">
803 below. If more than two arguments are provided then additional
804 arguments are taken as aliases for I<$object> as for C<define_alias>.
806 =head1 Encoding and IO
808 It is very common to want to do encoding transformations when
809 reading or writing files, network connections, pipes etc.
810 If Perl is configured to use the new 'perlio' IO system then
811 C<Encode> provides a "layer" (See L<perliol>) which can transform
812 data as it is read or written.
814 Here is how the blind poet would modernise the encoding:
817 open(my $iliad,'<:encoding(iso-8859-7)','iliad.greek');
818 open(my $utf8,'>:utf8','iliad.utf8');
824 In addition the new IO system can also be configured to read/write
825 UTF-8 encoded characters (as noted above this is efficient):
827 open(my $fh,'>:utf8','anything');
828 print $fh "Any \x{0021} string \N{SMILEY FACE}\n";
830 Either of the above forms of "layer" specifications can be made the default
831 for a lexical scope with the C<use open ...> pragma. See L<open>.
833 Once a handle is open is layers can be altered using C<binmode>.
835 Without any such configuration, or if Perl itself is built using
836 system's own IO, then write operations assume that file handle accepts
837 only I<bytes> and will C<die> if a character larger than 255 is
838 written to the handle. When reading, each octet from the handle
839 becomes a byte-in-a-character. Note that this default is the same
840 behaviour as bytes-only languages (including Perl before v5.6) would
841 have, and is sufficient to handle native 8-bit encodings
842 e.g. iso-8859-1, EBCDIC etc. and any legacy mechanisms for handling
843 other encodings and binary data.
845 In other cases it is the programs responsibility to transform
846 characters into bytes using the API above before doing writes, and to
847 transform the bytes read from a handle into characters before doing
848 "character operations" (e.g. C<lc>, C</\W+/>, ...).
850 You can also use PerlIO to convert larger amounts of data you don't
851 want to bring into memory. For example to convert between ISO 8859-1
852 (Latin 1) and UTF-8 (or UTF-EBCDIC in EBCDIC machines):
854 open(F, "<:encoding(iso-8859-1)", "data.txt") or die $!;
855 open(G, ">:utf8", "data.utf") or die $!;
856 while (<F>) { print G }
858 # Could also do "print G <F>" but that would pull
859 # the whole file into memory just to write it out again.
863 open(my $f, "<:encoding(cp1252)")
864 open(my $g, ">:encoding(iso-8859-2)")
865 open(my $h, ">:encoding(latin9)") # iso-8859-15
867 See L<PerlIO> for more information.
869 See also L<encoding> for how to change the default encoding of the
872 =head1 Encoding How to ...
878 =item * IO with mixed content (faking iso-2020-*)
880 =item * MIME's Content-Length:
882 =item * UTF-8 strings in binary data.
884 =item * Perl/Encode wrappers on non-Unicode XS modules.
888 =head1 Messing with Perl's Internals
890 The following API uses parts of Perl's internals in the current
891 implementation. As such they are efficient, but may change.
895 =item * is_utf8(STRING [, CHECK])
897 [INTERNAL] Test whether the UTF-8 flag is turned on in the STRING.
898 If CHECK is true, also checks the data in STRING for being well-formed
899 UTF-8. Returns true if successful, false otherwise.
901 =item * valid_utf8(STRING)
903 [INTERNAL] Test whether STRING is in a consistent state. Will return
904 true if string is held as bytes, or is well-formed UTF-8 and has the
905 UTF-8 flag on. Main reason for this routine is to allow Perl's
906 testsuite to check that operations have left strings in a consistent
913 [INTERNAL] Turn on the UTF-8 flag in STRING. The data in STRING is
914 B<not> checked for being well-formed UTF-8. Do not use unless you
915 B<know> that the STRING is well-formed UTF-8. Returns the previous
916 state of the UTF-8 flag (so please don't test the return value as
917 I<not> success or failure), or C<undef> if STRING is not a string.
923 [INTERNAL] Turn off the UTF-8 flag in STRING. Do not use frivolously.
924 Returns the previous state of the UTF-8 flag (so please don't test the
925 return value as I<not> success or failure), or C<undef> if STRING is
930 =head1 IMPLEMENTATION CLASSES
932 As mentioned above encodings are (in the current implementation at least)
933 defined by objects. The mapping of encoding name to object is via the
936 The values of the hash can currently be either strings or objects.
937 The string form may go away in the future. The string form occurs
938 when C<encodings()> has scanned C<@INC> for loadable encodings but has
939 not actually loaded the encoding in question. This is because the
940 current "loading" process is all Perl and a bit slow.
942 Once an encoding is loaded then value of the hash is object which
943 implements the encoding. The object should provide the following
950 Should return the string representing the canonical name of the encoding.
952 =item -E<gt>new_sequence
954 This is a placeholder for encodings with state. It should return an
955 object which implements this interface, all current implementations
956 return the original object.
958 =item -E<gt>encode($string,$check)
960 Should return the octet sequence representing I<$string>. If I<$check>
961 is true it should modify I<$string> in place to remove the converted
962 part (i.e. the whole string unless there is an error). If an error
963 occurs it should return the octet sequence for the fragment of string
964 that has been converted, and modify $string in-place to remove the
965 converted part leaving it starting with the problem fragment.
967 If check is is false then C<encode> should make a "best effort" to
968 convert the string - for example by using a replacement character.
970 =item -E<gt>decode($octets,$check)
972 Should return the string that I<$octets> represents. If I<$check> is
973 true it should modify I<$octets> in place to remove the converted part
974 (i.e. the whole sequence unless there is an error). If an error
975 occurs it should return the fragment of string that has been
976 converted, and modify $octets in-place to remove the converted part
977 leaving it starting with the problem fragment.
979 If check is is false then C<decode> should make a "best effort" to
980 convert the string - for example by using Unicode's "\x{FFFD}" as a
981 replacement character.
985 It should be noted that the check behaviour is different from the
986 outer public API. The logic is that the "unchecked" case is useful
987 when encoding is part of a stream which may be reporting errors
988 (e.g. STDERR). In such cases it is desirable to get everything
989 through somehow without causing additional errors which obscure the
990 original one. Also the encoding is best placed to know what the
991 correct replacement character is, so if that is the desired behaviour
992 then letting low level code do it is the most efficient.
994 In contrast if check is true, the scheme above allows the encoding to
995 do as much as it can and tell layer above how much that was. What is
996 lacking at present is a mechanism to report what went wrong. The most
997 likely interface will be an additional method call to the object, or
998 perhaps (to avoid forcing per-stream objects on otherwise stateless
999 encodings) and additional parameter.
1001 It is also highly desirable that encoding classes inherit from
1002 C<Encode::Encoding> as a base class. This allows that class to define
1003 additional behaviour for all encoding objects. For example built in
1004 Unicode, UCS-2 and UTF-8 classes use :
1006 package Encode::MyEncoding;
1007 use base qw(Encode::Encoding);
1009 __PACKAGE__->Define(qw(myCanonical myAlias));
1011 To create an object with bless {Name => ...},$class, and call
1012 define_encoding. They inherit their C<name> method from
1013 C<Encode::Encoding>.
1015 =head2 Compiled Encodings
1017 F<Encode.xs> provides a class C<Encode::XS> which provides the
1018 interface described above. It calls a generic octet-sequence to
1019 octet-sequence "engine" that is driven by tables (defined in
1020 F<encengine.c>). The same engine is used for both encode and
1021 decode. C<Encode:XS>'s C<encode> forces Perl's characters to their
1022 UTF-8 form and then treats them as just another multibyte
1023 encoding. C<Encode:XS>'s C<decode> transforms the sequence and then
1024 turns the UTF-8-ness flag as that is the form that the tables are
1025 defined to produce. For details of the engine see the comments in
1028 The tables are produced by the Perl script F<compile> (the name needs
1029 to change so we can eventually install it somewhere). F<compile> can
1030 currently read two formats:
1036 This is a coined format used by Tcl. It is documented in
1037 Encode/EncodeFormat.pod.
1041 This is the semi-standard format used by IBM's ICU package.
1045 F<compile> can write the following forms:
1051 See above - the F<Encode/*.ucm> files provided with the distribution have
1052 been created from the original Tcl .enc files using this approach.
1056 Produces tables as C data structures - this is used to build in encodings
1057 into F<Encode.so>/F<Encode.dll>.
1061 In theory this allows encodings to be stand-alone loadable Perl
1062 extensions. The process has not yet been tested. The plan is to use
1063 this approach for large East Asian encodings.
1067 The set of encodings built-in to F<Encode.so>/F<Encode.dll> is
1068 determined by F<Makefile.PL>. The current set is as follows:
1072 =item ascii and iso-8859-*
1074 That is all the common 8-bit "western" encodings.
1076 =item IBM-1047 and two other variants of EBCDIC.
1078 These are the same variants that are supported by EBCDIC Perl as
1079 "native" encodings. They are included to prove "reversibility" of
1080 some constructs in EBCDIC Perl.
1082 =item symbol and dingbats as used by Tk on X11.
1084 (The reason Encode got started was to support Perl/Tk.)
1088 That set is rather ad hoc and has been driven by the needs of the
1089 tests rather than the needs of typical applications. It is likely
1094 L<perlunicode>, L<perlebcdic>, L<perlfunc/open>, L<PerlIO>, L<encoding>