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)>.
465 =head2 Encoding Names
467 Encoding names are case insensitive. White space in names is ignored.
468 In addition an encoding may have aliases. Each encoding has one
469 "canonical" name. The "canonical" name is chosen from the names of
470 the encoding by picking the first in the following sequence:
474 =item * The MIME name as defined in IETF RFCs.
476 =item * The name in the IANA registry.
478 =item * The name used by the organization that defined it.
482 Because of all the alias issues, and because in the general case
483 encodings have state C<Encode> uses the encoding object internally
484 once an operation is in progress.
486 As of Perl 5.8.0, at least the following encodings are recognized
487 (the => marks aliases):
501 The ISO 8859 and KOI:
503 ISO 8859-1 ISO 8859-6 ISO 8859-11 KOI8-F
504 ISO 8859-2 ISO 8859-7 (12 doesn't exist) KOI8-R
505 ISO 8859-3 ISO 8859-8 ISO 8859-13 KOI8-U
506 ISO 8859-4 ISO 8859-9 ISO 8859-14
507 ISO 8859-5 ISO 8859-10 ISO 8859-15
510 Latin1 => 8859-1 Latin6 => 8859-10
511 Latin2 => 8859-2 Latin7 => 8859-13
512 Latin3 => 8859-3 Latin8 => 8859-14
513 Latin4 => 8859-4 Latin9 => 8859-15
514 Latin5 => 8859-9 Latin10 => 8859-16
523 The CJKV: Chinese, Japanese, Korean, Vietnamese:
525 ISO 2022 ISO 2022 JP-1 JIS 0201 GB 1988 Big5 EUC-CN
526 ISO 2022 CN ISO 2022 JP-2 JIS 0208 GB 2312 HZ EUC-JP
527 ISO 2022 JP ISO 2022 KR JIS 0210 GB 12345 CNS 11643 EUC-JP-0212
528 Shift-JIS GBK Big5-HKSCS EUC-KR
531 (Due to size concerns, additional Chinese encodings including C<GB 18030>,
532 C<EUC-TW> and C<BIG5PLUS> are distributed separately on CPAN, under the name
533 L<Encode::HanExtra>.)
537 CP37 CP852 CP861 CP866 CP949 CP1251 CP1256
538 CP424 CP855 CP862 CP869 CP950 CP1252 CP1257
539 CP737 CP856 CP863 CP874 CP1006 CP1253 CP1258
540 CP775 CP857 CP864 CP932 CP1047 CP1254
541 CP850 CP860 CP865 CP936 CP1250 CP1255
545 WinCyrillic => CP1251
547 WinTurkiskh => CP1254
551 WinVietnamese => CP1258
553 (All the CPI<NNN...> are available also as IBMI<NNN...>.)
557 MacCentralEuropean MacJapanese
559 MacCyrillic MacRomanian
562 MacIcelandic MacTurkish
573 =head1 PERL ENCODING API
575 =head2 Generic Encoding Interface
581 $bytes = encode(ENCODING, $string[, CHECK])
583 Encodes string from Perl's internal form into I<ENCODING> and returns
584 a sequence of octets. For CHECK see L</"Handling Malformed Data">.
586 For example to convert (internally UTF-8 encoded) Unicode data
589 $octets = encode("utf8", $unicode);
593 $string = decode(ENCODING, $bytes[, CHECK])
595 Decode sequence of octets assumed to be in I<ENCODING> into Perl's
596 internal form and returns the resulting string. For CHECK see
597 L</"Handling Malformed Data">.
599 For example to convert ISO 8859-1 data to UTF-8:
601 $utf8 = decode("latin1", $latin1);
605 from_to($string, FROM_ENCODING, TO_ENCODING[, CHECK])
607 Convert B<in-place> the data between two encodings. How did the data
608 in $string originally get to be in FROM_ENCODING? Either using
609 encode() or through PerlIO: See L</"Encoding and IO">. For CHECK
610 see L</"Handling Malformed Data">.
612 For example to convert ISO 8859-1 data to UTF-8:
614 from_to($data, "iso-8859-1", "utf-8");
616 and to convert it back:
618 from_to($data, "utf-8", "iso-8859-1");
620 Note that because the conversion happens in place, the data to be
621 converted cannot be a string constant, it must be a scalar variable.
625 =head2 Handling Malformed Data
627 If CHECK is not set, C<undef> is returned. If the data is supposed to
628 be UTF-8, an optional lexical warning (category utf8) is given. If
629 CHECK is true but not a code reference, dies.
631 It would desirable to have a way to indicate that transform should use
632 the encodings "replacement character" - no such mechanism is defined yet.
634 It is also planned to allow I<CHECK> to be a code reference.
636 This is not yet implemented as there are design issues with what its
637 arguments should be and how it returns its results.
643 Passed remaining fragment of string being processed.
644 Modifies it in place to remove bytes/characters it can understand
645 and returns a string used to represent them.
649 my $ch = substr($_[0],0,1,'');
650 return sprintf("\x{%02X}",ord($ch);
653 This scheme is close to how underlying C code for Encode works, but gives
654 the fixup routine very little context.
658 Passed original string, and an index into it of the problem area, and
659 output string so far. Appends what it will to output string and
660 returns new index into original string. For example:
663 # my ($s,$i,$d) = @_;
664 my $ch = substr($_[0],$_[1],1);
665 $_[2] .= sprintf("\x{%02X}",ord($ch);
669 This scheme gives maximal control to the fixup routine but is more
670 complicated to code, and may need internals of Encode to be tweaked to
671 keep original string intact.
677 Multiple return values rather than in-place modifications.
679 Index into the string could be pos($str) allowing s/\G...//.
685 The Unicode consortium defines the UTF-8 standard as a way of encoding
686 the entire Unicode repertiore as sequences of octets. This encoding is
687 expected to become very widespread. Perl can use this form internaly
688 to represent strings, so conversions to and from this form are
689 particularly efficient (as octets in memory do not have to change,
690 just the meta-data that tells Perl how to treat them).
696 $bytes = encode_utf8($string);
698 The characters that comprise string are encoded in Perl's superset of UTF-8
699 and the resulting octets returned as a sequence of bytes. All possible
700 characters have a UTF-8 representation so this function cannot fail.
704 $string = decode_utf8($bytes [,CHECK]);
706 The sequence of octets represented by $bytes is decoded from UTF-8
707 into a sequence of logical characters. Not all sequences of octets
708 form valid UTF-8 encodings, so it is possible for this call to fail.
709 For CHECK see L</"Handling Malformed Data">.
713 =head2 Other Encodings of Unicode
715 UTF-16 is similar to UCS-2, 16 bit or 2-byte chunks. UCS-2 can only
716 represent 0..0xFFFF, while UTF-16 has a I<surrogate pair> scheme which
717 allows it to cover the whole Unicode range.
719 Surrogates are code points set aside to encode the 0x01000..0x10FFFF
720 range of Unicode code points in pairs of 16-bit units. The I<high
721 surrogates> are the range 0xD800..0xDBFF, and the I<low surrogates>
722 are the range 0xDC00..0xDFFFF. The surrogate encoding is
724 $hi = ($uni - 0x10000) / 0x400 + 0xD800;
725 $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
729 $uni = 0x10000 + ($hi - 0xD8000) * 0x400 + ($lo - 0xDC00);
731 Encode implements big-endian UCS-2 aliased to "iso-10646-1" as that
732 happens to be the name used by that representation when used with X11
735 UTF-32 or UCS-4 is 32-bit or 4-byte chunks. Perl's logical characters
736 can be considered as being in this form without encoding. An encoding
737 to transfer strings in this form (e.g. to write them to a file) would
740 pack('L*', unpack('U*', $string)); # native
742 pack('V*', unpack('U*', $string)); # little-endian
744 pack('N*', unpack('U*', $string)); # big-endian
746 depending on the endianness required.
748 No UTF-32 encodings are implemented yet.
750 Both UCS-2 and UCS-4 style encodings can have "byte order marks" by
751 representing the code point 0xFFFE as the very first thing in a file.
753 =head2 Listing available encodings
755 use Encode qw(encodings);
758 Returns a list of the canonical names of the available encodings.
760 =head2 Defining Aliases
762 use Encode qw(define_alias);
763 define_alias( newName => ENCODING);
765 Allows newName to be used as am alias for ENCODING. ENCODING may be
766 either the name of an encoding or and encoding object (as above).
768 Currently I<newName> can be specified in the following ways:
772 =item As a simple string.
774 =item As a qr// compiled regular expression, e.g.:
776 define_alias( qr/^iso8859-(\d+)$/i => '"iso-8859-$1"' );
778 In this case if I<ENCODING> is not a reference it is C<eval>-ed to
779 allow C<$1> etc. to be subsituted. The example is one way to names as
780 used in X11 font names to alias the MIME names for the iso-8859-*
783 =item As a code reference, e.g.:
785 define_alias( sub { return /^iso8859-(\d+)$/i ? "iso-8859-$1" : undef } , '');
787 In this case C<$_> will be set to the name that is being looked up and
788 I<ENCODING> is passed to the sub as its first argument. The example
789 is another way to names as used in X11 font names to alias the MIME
790 names for the iso-8859-* family.
794 =head2 Defining Encodings
796 use Encode qw(define_alias);
797 define_encoding( $object, 'canonicalName' [,alias...]);
799 Causes I<canonicalName> to be associated with I<$object>. The object
800 should provide the interface described in L</"IMPLEMENTATION CLASSES">
801 below. If more than two arguments are provided then additional
802 arguments are taken as aliases for I<$object> as for C<define_alias>.
804 =head1 Encoding and IO
806 It is very common to want to do encoding transformations when
807 reading or writing files, network connections, pipes etc.
808 If Perl is configured to use the new 'perlio' IO system then
809 C<Encode> provides a "layer" (See L<perliol>) which can transform
810 data as it is read or written.
812 Here is how the blind poet would modernise the encoding:
815 open(my $iliad,'<:encoding(iso-8859-7)','iliad.greek');
816 open(my $utf8,'>:utf8','iliad.utf8');
822 In addition the new IO system can also be configured to read/write
823 UTF-8 encoded characters (as noted above this is efficient):
825 open(my $fh,'>:utf8','anything');
826 print $fh "Any \x{0021} string \N{SMILEY FACE}\n";
828 Either of the above forms of "layer" specifications can be made the default
829 for a lexical scope with the C<use open ...> pragma. See L<open>.
831 Once a handle is open is layers can be altered using C<binmode>.
833 Without any such configuration, or if Perl itself is built using
834 system's own IO, then write operations assume that file handle accepts
835 only I<bytes> and will C<die> if a character larger than 255 is
836 written to the handle. When reading, each octet from the handle
837 becomes a byte-in-a-character. Note that this default is the same
838 behaviour as bytes-only languages (including Perl before v5.6) would
839 have, and is sufficient to handle native 8-bit encodings
840 e.g. iso-8859-1, EBCDIC etc. and any legacy mechanisms for handling
841 other encodings and binary data.
843 In other cases it is the programs responsibility to transform
844 characters into bytes using the API above before doing writes, and to
845 transform the bytes read from a handle into characters before doing
846 "character operations" (e.g. C<lc>, C</\W+/>, ...).
848 You can also use PerlIO to convert larger amounts of data you don't
849 want to bring into memory. For example to convert between ISO 8859-1
850 (Latin 1) and UTF-8 (or UTF-EBCDIC in EBCDIC machines):
852 open(F, "<:encoding(iso-8859-1)", "data.txt") or die $!;
853 open(G, ">:utf8", "data.utf") or die $!;
854 while (<F>) { print G }
856 # Could also do "print G <F>" but that would pull
857 # the whole file into memory just to write it out again.
861 open(my $f, "<:encoding(cp1252)")
862 open(my $g, ">:encoding(iso-8859-2)")
863 open(my $h, ">:encoding(latin9)") # iso-8859-15
865 See L<PerlIO> for more information.
867 See also L<encoding> for how to change the default encoding of the
870 =head1 Encoding How to ...
876 =item * IO with mixed content (faking iso-2020-*)
878 =item * MIME's Content-Length:
880 =item * UTF-8 strings in binary data.
882 =item * Perl/Encode wrappers on non-Unicode XS modules.
886 =head1 Messing with Perl's Internals
888 The following API uses parts of Perl's internals in the current
889 implementation. As such they are efficient, but may change.
893 =item * is_utf8(STRING [, CHECK])
895 [INTERNAL] Test whether the UTF-8 flag is turned on in the STRING.
896 If CHECK is true, also checks the data in STRING for being well-formed
897 UTF-8. Returns true if successful, false otherwise.
899 =item * valid_utf8(STRING)
901 [INTERNAL] Test whether STRING is in a consistent state. Will return
902 true if string is held as bytes, or is well-formed UTF-8 and has the
903 UTF-8 flag on. Main reason for this routine is to allow Perl's
904 testsuite to check that operations have left strings in a consistent
911 [INTERNAL] Turn on the UTF-8 flag in STRING. The data in STRING is
912 B<not> checked for being well-formed UTF-8. Do not use unless you
913 B<know> that the STRING is well-formed UTF-8. Returns the previous
914 state of the UTF-8 flag (so please don't test the return value as
915 I<not> success or failure), or C<undef> if STRING is not a string.
921 [INTERNAL] Turn off the UTF-8 flag in STRING. Do not use frivolously.
922 Returns the previous state of the UTF-8 flag (so please don't test the
923 return value as I<not> success or failure), or C<undef> if STRING is
928 =head1 IMPLEMENTATION CLASSES
930 As mentioned above encodings are (in the current implementation at least)
931 defined by objects. The mapping of encoding name to object is via the
934 The values of the hash can currently be either strings or objects.
935 The string form may go away in the future. The string form occurs
936 when C<encodings()> has scanned C<@INC> for loadable encodings but has
937 not actually loaded the encoding in question. This is because the
938 current "loading" process is all Perl and a bit slow.
940 Once an encoding is loaded then value of the hash is object which
941 implements the encoding. The object should provide the following
948 Should return the string representing the canonical name of the encoding.
950 =item -E<gt>new_sequence
952 This is a placeholder for encodings with state. It should return an
953 object which implements this interface, all current implementations
954 return the original object.
956 =item -E<gt>encode($string,$check)
958 Should return the octet sequence representing I<$string>. If I<$check>
959 is true it should modify I<$string> in place to remove the converted
960 part (i.e. the whole string unless there is an error). If an error
961 occurs it should return the octet sequence for the fragment of string
962 that has been converted, and modify $string in-place to remove the
963 converted part leaving it starting with the problem fragment.
965 If check is is false then C<encode> should make a "best effort" to
966 convert the string - for example by using a replacement character.
968 =item -E<gt>decode($octets,$check)
970 Should return the string that I<$octets> represents. If I<$check> is
971 true it should modify I<$octets> in place to remove the converted part
972 (i.e. the whole sequence unless there is an error). If an error
973 occurs it should return the fragment of string that has been
974 converted, and modify $octets in-place to remove the converted part
975 leaving it starting with the problem fragment.
977 If check is is false then C<decode> should make a "best effort" to
978 convert the string - for example by using Unicode's "\x{FFFD}" as a
979 replacement character.
983 It should be noted that the check behaviour is different from the
984 outer public API. The logic is that the "unchecked" case is useful
985 when encoding is part of a stream which may be reporting errors
986 (e.g. STDERR). In such cases it is desirable to get everything
987 through somehow without causing additional errors which obscure the
988 original one. Also the encoding is best placed to know what the
989 correct replacement character is, so if that is the desired behaviour
990 then letting low level code do it is the most efficient.
992 In contrast if check is true, the scheme above allows the encoding to
993 do as much as it can and tell layer above how much that was. What is
994 lacking at present is a mechanism to report what went wrong. The most
995 likely interface will be an additional method call to the object, or
996 perhaps (to avoid forcing per-stream objects on otherwise stateless
997 encodings) and additional parameter.
999 It is also highly desirable that encoding classes inherit from
1000 C<Encode::Encoding> as a base class. This allows that class to define
1001 additional behaviour for all encoding objects. For example built in
1002 Unicode, UCS-2 and UTF-8 classes use :
1004 package Encode::MyEncoding;
1005 use base qw(Encode::Encoding);
1007 __PACKAGE__->Define(qw(myCanonical myAlias));
1009 To create an object with bless {Name => ...},$class, and call
1010 define_encoding. They inherit their C<name> method from
1011 C<Encode::Encoding>.
1013 =head2 Compiled Encodings
1015 F<Encode.xs> provides a class C<Encode::XS> which provides the
1016 interface described above. It calls a generic octet-sequence to
1017 octet-sequence "engine" that is driven by tables (defined in
1018 F<encengine.c>). The same engine is used for both encode and
1019 decode. C<Encode:XS>'s C<encode> forces Perl's characters to their
1020 UTF-8 form and then treats them as just another multibyte
1021 encoding. C<Encode:XS>'s C<decode> transforms the sequence and then
1022 turns the UTF-8-ness flag as that is the form that the tables are
1023 defined to produce. For details of the engine see the comments in
1026 The tables are produced by the Perl script F<compile> (the name needs
1027 to change so we can eventually install it somewhere). F<compile> can
1028 currently read two formats:
1034 This is a coined format used by Tcl. It is documented in
1035 Encode/EncodeFormat.pod.
1039 This is the semi-standard format used by IBM's ICU package.
1043 F<compile> can write the following forms:
1049 See above - the F<Encode/*.ucm> files provided with the distribution have
1050 been created from the original Tcl .enc files using this approach.
1054 Produces tables as C data structures - this is used to build in encodings
1055 into F<Encode.so>/F<Encode.dll>.
1059 In theory this allows encodings to be stand-alone loadable Perl
1060 extensions. The process has not yet been tested. The plan is to use
1061 this approach for large East Asian encodings.
1065 The set of encodings built-in to F<Encode.so>/F<Encode.dll> is
1066 determined by F<Makefile.PL>. The current set is as follows:
1070 =item ascii and iso-8859-*
1072 That is all the common 8-bit "western" encodings.
1074 =item IBM-1047 and two other variants of EBCDIC.
1076 These are the same variants that are supported by EBCDIC Perl as
1077 "native" encodings. They are included to prove "reversibility" of
1078 some constructs in EBCDIC Perl.
1080 =item symbol and dingbats as used by Tk on X11.
1082 (The reason Encode got started was to support Perl/Tk.)
1086 That set is rather ad hoc and has been driven by the needs of the
1087 tests rather than the needs of typical applications. It is likely
1092 L<perlunicode>, L<perlebcdic>, L<perlfunc/open>, L<PerlIO>, L<encoding>