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 );
64 return keys %encoding;
71 # print "# findAlias $_\n";
72 unless (exists $alias{$_})
74 for (my $i=0; $i < @alias; $i += 2)
76 my $alias = $alias[$i];
77 my $val = $alias[$i+1];
79 if (ref($alias) eq 'Regexp' && $_ =~ $alias)
83 elsif (ref($alias) eq 'CODE')
85 $new = &{$alias}($val)
87 elsif (lc($_) eq lc($alias))
93 next if $new eq $_; # avoid (direct) recursion on bugs
94 my $enc = (ref($new)) ? $new : find_encoding($new);
110 my ($alias,$name) = splice(@_,0,2);
111 push(@alias, $alias => $name);
115 # Allow variants of iso-8859-1 etc.
116 define_alias( qr/^iso[-_]?(\d+)[-_](\d+)$/i => '"iso-$1-$2"' );
118 # At least HP-UX has these.
119 define_alias( qr/^iso8859(\d+)$/i => '"iso-8859-$1"' );
122 define_alias( qr/^(?:hp-)?(arabic|greek|hebrew|kana|roman|thai|turkish)8$/i => '"${1}8"' );
124 # The Official name of ASCII.
125 define_alias( qr/^ANSI[-_]?X3\.4[-_]?1968$/i => '"ascii"' );
127 # This is a font issue, not an encoding issue.
128 # (The currency symbol of the Latin 1 upper half
129 # has been redefined as the euro symbol.)
130 define_alias( qr/^(.+)\@euro$/i => '"$1"' );
132 # Allow latin-1 style names as well
133 define_alias( qr/^(?:iso[-_]?)?latin[-_]?(\d+)$/i => '"iso-8859-$latin2iso_num[$1]"' );
135 # Allow winlatin1 style names as well
136 define_alias( qr/^win(latin[12]|cyrillic|baltic|greek|turkish|hebrew|arabic|baltic|vietnamese)$/i => '"cp$winlatin2cp{\u$1}"' );
138 # Common names for non-latin prefered MIME names
139 define_alias( 'ascii' => 'US-ascii',
140 'cyrillic' => 'iso-8859-5',
141 'arabic' => 'iso-8859-6',
142 'greek' => 'iso-8859-7',
143 'hebrew' => 'iso-8859-8',
144 'thai' => 'iso-8859-11',
145 'tis620' => 'iso-8859-11',
148 # At least AIX has IBM-NNN (surprisingly...) instead of cpNNN.
149 define_alias( qr/^ibm[-_]?(\d\d\d\d?)$/i => '"cp$1"');
151 # Standardize on the dashed versions.
152 define_alias( qr/^utf8$/i => 'utf-8' );
153 define_alias( qr/^koi8r$/i => 'koi8-r' );
154 define_alias( qr/^koi8u$/i => 'koi8-u' );
156 # TODO: HP-UX '8' encodings arabic8 greek8 hebrew8 kana8 thai8 turkish8
157 # TODO: HP-UX '15' encodings japanese15 korean15 roi15
158 # TODO: Cyrillic encoding ISO-IR-111 (useful?)
159 # TODO: Chinese encodings GB18030 GBK Big5-HSKCS EUC-TW
160 # TODO: Armenian encoding ARMSCII-8
161 # TODO: Hebrew encoding ISO-8859-8-1
162 # TODO: Thai encoding TCVN
163 # TODO: Korean encoding Johab
164 # TODO: Vietnamese encodings VPS
165 # TODO: Japanese encoding JIS (not the same as SJIS)
166 # TODO: Mac Asian+African encodings: Arabic Armenian Bengali Burmese
167 # ChineseSimp ChineseTrad Devanagari Ethiopic ExtArabic
168 # Farsi Georgian Gujarati Gurmukhi Hebrew Japanese
169 # Kannada Khmer Korean Laotian Malayalam Mongolian
170 # Oriya Sinhalese Symbol Tamil Telugu Tibetan Vietnamese
171 # TODO: what is the Japanese 'UJIS' encoding seen in some Linuxes?
173 # Map white space and _ to '-'
174 define_alias( qr/^(\S+)[\s_]+(.*)$/i => '"$1-$2"' );
180 $encoding{$name} = $obj;
182 define_alias($lc => $obj) unless $lc eq $name;
186 define_alias($alias,$obj);
193 my ($class,$name) = @_;
195 if (ref($name) && $name->can('new_sequence'))
200 if (exists $encoding{$name})
202 return $encoding{$name};
204 if (exists $encoding{$lc})
206 return $encoding{$lc};
209 my $oc = $class->findAlias($name);
210 return $oc if defined $oc;
211 return $class->findAlias($lc) if $lc ne $name;
219 return __PACKAGE__->getEncoding($name);
224 my ($name,$string,$check) = @_;
225 my $enc = find_encoding($name);
226 croak("Unknown encoding '$name'") unless defined $enc;
227 my $octets = $enc->encode($string,$check);
228 return undef if ($check && length($string));
234 my ($name,$octets,$check) = @_;
235 my $enc = find_encoding($name);
236 croak("Unknown encoding '$name'") unless defined $enc;
237 my $string = $enc->decode($octets,$check);
238 $_[1] = $octets if $check;
244 my ($string,$from,$to,$check) = @_;
245 my $f = find_encoding($from);
246 croak("Unknown encoding '$from'") unless defined $f;
247 my $t = find_encoding($to);
248 croak("Unknown encoding '$to'") unless defined $t;
249 my $uni = $f->decode($string,$check);
250 return undef if ($check && length($string));
251 $string = $t->encode($uni,$check);
252 return undef if ($check && length($uni));
253 return length($_[0] = $string);
266 return undef unless utf8::decode($str);
270 package Encode::Encoding;
271 # Base class for classes which implement encodings
276 my $canonical = shift;
277 $obj = bless { Name => $canonical },$obj unless ref $obj;
278 # warn "$canonical => $obj\n";
279 Encode::define_encoding($obj, $canonical, @_);
282 sub name { shift->{'Name'} }
284 # Temporary legacy methods
285 sub toUnicode { shift->decode(@_) }
286 sub fromUnicode { shift->encode(@_) }
288 sub new_sequence { return $_[0] }
291 use base 'Encode::Encoding';
293 package Encode::Internal;
294 use base 'Encode::Encoding';
296 # Dummy package that provides the encode interface but leaves data
297 # as UTF-X encoded. It is here so that from_to() works.
299 __PACKAGE__->Define('Internal');
301 Encode::define_alias( 'Unicode' => 'Internal' ) if ord('A') == 65;
305 my ($obj,$str,$chk) = @_;
313 package Encoding::Unicode;
314 use base 'Encode::Encoding';
316 __PACKAGE__->Define('Unicode') unless ord('A') == 65;
320 my ($obj,$str,$chk) = @_;
322 for (my $i = 0; $i < length($str); $i++)
324 $res .= chr(utf8::unicode_to_native(ord(substr($str,$i,1))));
332 my ($obj,$str,$chk) = @_;
334 for (my $i = 0; $i < length($str); $i++)
336 $res .= chr(utf8::native_to_unicode(ord(substr($str,$i,1))));
343 package Encode::utf8;
344 use base 'Encode::Encoding';
345 # package to allow long-hand
346 # $octets = encode( utf8 => $string );
349 __PACKAGE__->Define(qw(UTF-8 utf8));
353 my ($obj,$octets,$chk) = @_;
354 my $str = Encode::decode_utf8($octets);
365 my ($obj,$string,$chk) = @_;
366 my $octets = Encode::encode_utf8($string);
371 package Encode::iso10646_1;
372 use base 'Encode::Encoding';
373 # Encoding is 16-bit network order Unicode (no surogates)
374 # Used for X font encodings
376 __PACKAGE__->Define(qw(UCS-2 iso-10646-1));
380 my ($obj,$str,$chk) = @_;
384 my $code = unpack('n',substr($str,0,2,'')) & 0xffff;
387 $_[1] = $str if $chk;
394 my ($obj,$uni,$chk) = @_;
398 my $ch = substr($uni,0,1,'');
405 $str .= pack('n',$x);
407 $_[1] = $uni if $chk;
411 package Encode::ucs_2le;
412 use base 'Encode::Encoding';
414 __PACKAGE__->Define(qw(UCS-2le UCS-2LE ucs-2le));
418 my ($obj,$str,$chk) = @_;
422 my $code = unpack('v',substr($str,0,2,'')) & 0xffff;
425 $_[1] = $str if $chk;
432 my ($obj,$uni,$chk) = @_;
436 my $ch = substr($uni,0,1,'');
443 $str .= pack('v',$x);
445 $_[1] = $uni if $chk;
449 # switch back to Encode package in case we ever add AutoLoader
458 Encode - character encodings
466 The C<Encode> module provides the interfaces between Perl's strings
467 and the rest of the system. Perl strings are sequences of B<characters>.
469 The repertoire of characters that Perl can represent is at least that
470 defined by the Unicode Consortium. On most platforms the ordinal
471 values of the characters (as returned by C<ord(ch)>) is the "Unicode
472 codepoint" for the character (the exceptions are those platforms where
473 the legacy encoding is some variant of EBCDIC rather than a super-set
474 of ASCII - see L<perlebcdic>).
476 Traditionaly computer data has been moved around in 8-bit chunks
477 often called "bytes". These chunks are also known as "octets" in
478 networking standards. Perl is widely used to manipulate data of
479 many types - not only strings of characters representing human or
480 computer languages but also "binary" data being the machines representation
481 of numbers, pixels in an image - or just about anything.
483 When Perl is processing "binary data" the programmer wants Perl to process
484 "sequences of bytes". This is not a problem for Perl - as a byte has 256
485 possible values it easily fits in Perl's much larger "logical character".
493 I<character>: a character in the range 0..(2**32-1) (or more).
494 (What Perl's strings are made of.)
498 I<byte>: a character in the range 0..255
499 (A special case of a Perl character.)
503 I<octet>: 8 bits of data, with ordinal values 0..255
504 (Term for bytes passed to or from a non-Perl context, e.g. disk file.)
508 The marker [INTERNAL] marks Internal Implementation Details, in
509 general meant only for those who think they know what they are doing,
510 and such details may change in future releases.
514 =head2 Characteristics of an Encoding
516 An encoding has a "repertoire" of characters that it can represent,
517 and for each representable character there is at least one sequence of
518 octets that represents it.
520 =head2 Types of Encodings
522 Encodings can be divided into the following types:
526 =item * Fixed length 8-bit (or less) encodings.
528 Each character is a single octet so may have a repertoire of up to
529 256 characters. ASCII and iso-8859-* are typical examples.
531 =item * Fixed length 16-bit encodings
533 Each character is two octets so may have a repertoire of up to
534 65 536 characters. Unicode's UCS-2 is an example. Also used for
535 encodings for East Asian languages.
537 =item * Fixed length 32-bit encodings.
539 Not really very "encoded" encodings. The Unicode code points
540 are just represented as 4-octet integers. None the less because
541 different architectures use different representations of integers
542 (so called "endian") there at least two disctinct encodings.
544 =item * Multi-byte encodings
546 The number of octets needed to represent a character varies.
547 UTF-8 is a particularly complex but regular case of a multi-byte
548 encoding. Several East Asian countries use a multi-byte encoding
549 where 1-octet is used to cover western roman characters and Asian
550 characters get 2-octets.
551 (UTF-16 is strictly a multi-byte encoding taking either 2 or 4 octets
552 to represent a Unicode code point.)
554 =item * "Escape" encodings.
556 These encodings embed "escape sequences" into the octet sequence
557 which describe how the following octets are to be interpreted.
558 The iso-2022-* family is typical. Following the escape sequence
559 octets are encoded by an "embedded" encoding (which will be one
560 of the above types) until another escape sequence switches to
561 a different "embedded" encoding.
563 These schemes are very flexible and can handle mixed languages but are
564 very complex to process (and have state). No escape encodings are
565 implemented for Perl yet.
569 =head2 Specifying Encodings
571 Encodings can be specified to the API described below in two ways:
577 Encoding names are strings with characters taken from a restricted
578 repertoire. See L</"Encoding Names">.
580 =item 2. As an object
582 Encoding objects are returned by C<find_encoding($name)>.
586 =head2 Encoding Names
588 Encoding names are case insensitive. White space in names is ignored.
589 In addition an encoding may have aliases. Each encoding has one
590 "canonical" name. The "canonical" name is chosen from the names of
591 the encoding by picking the first in the following sequence:
595 =item * The MIME name as defined in IETF RFCs.
597 =item * The name in the IANA registry.
599 =item * The name used by the organization that defined it.
603 Because of all the alias issues, and because in the general case
604 encodings have state C<Encode> uses the encoding object internally
605 once an operation is in progress.
607 As of Perl 5.8.0, at least the following encodings are recognized
608 (the => marks aliases):
622 The ISO 8859 and KOI:
624 ISO 8859-1 ISO 8859-6 ISO 8859-11 KOI8-F
625 ISO 8859-2 ISO 8859-7 (12 doesn't exist) KOI8-R
626 ISO 8859-3 ISO 8859-8 ISO 8859-13 KOI8-U
627 ISO 8859-4 ISO 8859-9 ISO 8859-14
628 ISO 8859-5 ISO 8859-10 ISO 8859-15
631 Latin1 => 8859-1 Latin6 => 8859-10
632 Latin2 => 8859-2 Latin7 => 8859-13
633 Latin3 => 8859-3 Latin8 => 8859-14
634 Latin4 => 8859-4 Latin9 => 8859-15
635 Latin5 => 8859-9 Latin10 => 8859-16
644 The CJKV: Chinese, Japanese, Korean, Vietnamese:
646 ISO 2022 ISO 2022 JP-1 JIS 0201 GB 1988 Big5 EUC-CN
647 ISO 2022 CN ISO 2022 JP-2 JIS 0208 GB 2312 HZ EUC-JP
648 ISO 2022 JP ISO 2022 KR JIS 0210 GB 12345 CNS 11643 EUC-JP-0212
654 CP37 CP852 CP861 CP866 CP949 CP1251 CP1256
655 CP424 CP855 CP862 CP869 CP950 CP1252 CP1257
656 CP737 CP856 CP863 CP874 CP1006 CP1253 CP1258
657 CP775 CP857 CP864 CP932 CP1047 CP1254
658 CP850 CP860 CP865 CP936 CP1250 CP1255
662 WinCyrillic => CP1251
664 WinTurkiskh => CP1254
668 WinVietnamese => CP1258
670 (All the CPI<NNN...> are available also as IBMI<NNN...>.)
674 MacCentralEuropean MacJapanese
676 MacCyrillic MacRumanian
679 MacIcelandic MacTurkish
690 =head1 PERL ENCODING API
692 =head2 Generic Encoding Interface
698 $bytes = encode(ENCODING, $string[, CHECK])
700 Encodes string from Perl's internal form into I<ENCODING> and returns
701 a sequence of octets. For CHECK see L</"Handling Malformed Data">.
705 $string = decode(ENCODING, $bytes[, CHECK])
707 Decode sequence of octets assumed to be in I<ENCODING> into Perl's
708 internal form and returns the resulting string. For CHECK see
709 L</"Handling Malformed Data">.
713 from_to($string, FROM_ENCODING, TO_ENCODING[, CHECK])
715 Convert B<in-place> the data between two encodings. How did the data
716 in $string originally get to be in FROM_ENCODING? Either using
717 encode() or through PerlIO: See L</"Encoding and IO">. For CHECK
718 see L</"Handling Malformed Data">.
720 For example to convert ISO 8859-1 data to UTF-8:
722 from_to($data, "iso-8859-1", "utf-8");
724 and to convert it back:
726 from_to($data, "utf-8", "iso-8859-1");
728 Note that because the conversion happens in place, the data to be
729 converted cannot be a string constant, it must be a scalar variable.
733 =head2 Handling Malformed Data
735 If CHECK is not set, C<undef> is returned. If the data is supposed to
736 be UTF-8, an optional lexical warning (category utf8) is given. If
737 CHECK is true but not a code reference, dies.
739 It would desirable to have a way to indicate that transform should use
740 the encodings "replacement character" - no such mechanism is defined yet.
742 It is also planned to allow I<CHECK> to be a code reference.
744 This is not yet implemented as there are design issues with what its
745 arguments should be and how it returns its results.
751 Passed remaining fragment of string being processed.
752 Modifies it in place to remove bytes/characters it can understand
753 and returns a string used to represent them.
757 my $ch = substr($_[0],0,1,'');
758 return sprintf("\x{%02X}",ord($ch);
761 This scheme is close to how underlying C code for Encode works, but gives
762 the fixup routine very little context.
766 Passed original string, and an index into it of the problem area, and
767 output string so far. Appends what it will to output string and
768 returns new index into original string. For example:
771 # my ($s,$i,$d) = @_;
772 my $ch = substr($_[0],$_[1],1);
773 $_[2] .= sprintf("\x{%02X}",ord($ch);
777 This scheme gives maximal control to the fixup routine but is more
778 complicated to code, and may need internals of Encode to be tweaked to
779 keep original string intact.
785 Multiple return values rather than in-place modifications.
787 Index into the string could be pos($str) allowing s/\G...//.
793 The Unicode consortium defines the UTF-8 standard as a way of encoding
794 the entire Unicode repertiore as sequences of octets. This encoding is
795 expected to become very widespread. Perl can use this form internaly
796 to represent strings, so conversions to and from this form are
797 particularly efficient (as octets in memory do not have to change,
798 just the meta-data that tells Perl how to treat them).
804 $bytes = encode_utf8($string);
806 The characters that comprise string are encoded in Perl's superset of UTF-8
807 and the resulting octets returned as a sequence of bytes. All possible
808 characters have a UTF-8 representation so this function cannot fail.
812 $string = decode_utf8($bytes [,CHECK]);
814 The sequence of octets represented by $bytes is decoded from UTF-8
815 into a sequence of logical characters. Not all sequences of octets
816 form valid UTF-8 encodings, so it is possible for this call to fail.
817 For CHECK see L</"Handling Malformed Data">.
821 =head2 Other Encodings of Unicode
823 UTF-16 is similar to UCS-2, 16 bit or 2-byte chunks. UCS-2 can only
824 represent 0..0xFFFF, while UTF-16 has a I<surrogate pair> scheme which
825 allows it to cover the whole Unicode range.
827 Surrogates are code points set aside to encode the 0x01000..0x10FFFF
828 range of Unicode code points in pairs of 16-bit units. The I<high
829 surrogates> are the range 0xD800..0xDBFF, and the I<low surrogates>
830 are the range 0xDC00..0xDFFFF. The surrogate encoding is
832 $hi = ($uni - 0x10000) / 0x400 + 0xD800;
833 $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
837 $uni = 0x10000 + ($hi - 0xD8000) * 0x400 + ($lo - 0xDC00);
839 Encode implements big-endian UCS-2 aliased to "iso-10646-1" as that
840 happens to be the name used by that representation when used with X11
843 UTF-32 or UCS-4 is 32-bit or 4-byte chunks. Perl's logical characters
844 can be considered as being in this form without encoding. An encoding
845 to transfer strings in this form (e.g. to write them to a file) would
848 pack('L*', unpack('U*', $string)); # native
850 pack('V*', unpack('U*', $string)); # little-endian
852 pack('N*', unpack('U*', $string)); # big-endian
854 depending on the endianness required.
856 No UTF-32 encodings are implemented yet.
858 Both UCS-2 and UCS-4 style encodings can have "byte order marks" by
859 representing the code point 0xFFFE as the very first thing in a file.
861 =head2 Listing available encodings
863 use Encode qw(encodings);
866 Returns a list of the canonical names of the available encodings.
868 =head2 Defining Aliases
870 use Encode qw(define_alias);
871 define_alias( newName => ENCODING);
873 Allows newName to be used as am alias for ENCODING. ENCODING may be
874 either the name of an encoding or and encoding object (as above).
876 Currently I<newName> can be specified in the following ways:
880 =item As a simple string.
882 =item As a qr// compiled regular expression, e.g.:
884 define_alias( qr/^iso8859-(\d+)$/i => '"iso-8859-$1"' );
886 In this case if I<ENCODING> is not a reference it is C<eval>-ed to
887 allow C<$1> etc. to be subsituted. The example is one way to names as
888 used in X11 font names to alias the MIME names for the iso-8859-*
891 =item As a code reference, e.g.:
893 define_alias( sub { return /^iso8859-(\d+)$/i ? "iso-8859-$1" : undef } , '');
895 In this case C<$_> will be set to the name that is being looked up and
896 I<ENCODING> is passed to the sub as its first argument. The example
897 is another way to names as used in X11 font names to alias the MIME
898 names for the iso-8859-* family.
902 =head2 Defining Encodings
904 use Encode qw(define_alias);
905 define_encoding( $object, 'canonicalName' [,alias...]);
907 Causes I<canonicalName> to be associated with I<$object>. The object
908 should provide the interface described in L</"IMPLEMENTATION CLASSES">
909 below. If more than two arguments are provided then additional
910 arguments are taken as aliases for I<$object> as for C<define_alias>.
912 =head1 Encoding and IO
914 It is very common to want to do encoding transformations when
915 reading or writing files, network connections, pipes etc.
916 If Perl is configured to use the new 'perlio' IO system then
917 C<Encode> provides a "layer" (See L<perliol>) which can transform
918 data as it is read or written.
920 Here is how the blind poet would modernise the encoding:
923 open(my $iliad,'<:encoding(iso-8859-7)','iliad.greek');
924 open(my $utf8,'>:utf8','iliad.utf8');
930 In addition the new IO system can also be configured to read/write
931 UTF-8 encoded characters (as noted above this is efficient):
933 open(my $fh,'>:utf8','anything');
934 print $fh "Any \x{0021} string \N{SMILEY FACE}\n";
936 Either of the above forms of "layer" specifications can be made the default
937 for a lexical scope with the C<use open ...> pragma. See L<open>.
939 Once a handle is open is layers can be altered using C<binmode>.
941 Without any such configuration, or if Perl itself is built using
942 system's own IO, then write operations assume that file handle accepts
943 only I<bytes> and will C<die> if a character larger than 255 is
944 written to the handle. When reading, each octet from the handle
945 becomes a byte-in-a-character. Note that this default is the same
946 behaviour as bytes-only languages (including Perl before v5.6) would
947 have, and is sufficient to handle native 8-bit encodings
948 e.g. iso-8859-1, EBCDIC etc. and any legacy mechanisms for handling
949 other encodings and binary data.
951 In other cases it is the programs responsibility to transform
952 characters into bytes using the API above before doing writes, and to
953 transform the bytes read from a handle into characters before doing
954 "character operations" (e.g. C<lc>, C</\W+/>, ...).
956 You can also use PerlIO to convert larger amounts of data you don't
957 want to bring into memory. For example to convert between ISO 8859-1
958 (Latin 1) and UTF-8 (or UTF-EBCDIC in EBCDIC machines):
960 open(F, "<:encoding(iso-8859-1)", "data.txt") or die $!;
961 open(G, ">:utf8", "data.utf") or die $!;
962 while (<F>) { print G }
964 # Could also do "print G <F>" but that would pull
965 # the whole file into memory just to write it out again.
969 open(my $f, "<:encoding(cp1252)")
970 open(my $g, ">:encoding(iso-8859-2)")
971 open(my $h, ">:encoding(latin9)") # iso-8859-15
973 See L<PerlIO> for more information.
975 See also L<encoding> for how to change the default encoding of the
978 =head1 Encoding How to ...
984 =item * IO with mixed content (faking iso-2020-*)
986 =item * MIME's Content-Length:
988 =item * UTF-8 strings in binary data.
990 =item * Perl/Encode wrappers on non-Unicode XS modules.
994 =head1 Messing with Perl's Internals
996 The following API uses parts of Perl's internals in the current
997 implementation. As such they are efficient, but may change.
1001 =item * is_utf8(STRING [, CHECK])
1003 [INTERNAL] Test whether the UTF-8 flag is turned on in the STRING.
1004 If CHECK is true, also checks the data in STRING for being well-formed
1005 UTF-8. Returns true if successful, false otherwise.
1007 =item * valid_utf8(STRING)
1009 [INTERNAL] Test whether STRING is in a consistent state. Will return
1010 true if string is held as bytes, or is well-formed UTF-8 and has the
1011 UTF-8 flag on. Main reason for this routine is to allow Perl's
1012 testsuite to check that operations have left strings in a consistent
1019 [INTERNAL] Turn on the UTF-8 flag in STRING. The data in STRING is
1020 B<not> checked for being well-formed UTF-8. Do not use unless you
1021 B<know> that the STRING is well-formed UTF-8. Returns the previous
1022 state of the UTF-8 flag (so please don't test the return value as
1023 I<not> success or failure), or C<undef> if STRING is not a string.
1029 [INTERNAL] Turn off the UTF-8 flag in STRING. Do not use frivolously.
1030 Returns the previous state of the UTF-8 flag (so please don't test the
1031 return value as I<not> success or failure), or C<undef> if STRING is
1036 =head1 IMPLEMENTATION CLASSES
1038 As mentioned above encodings are (in the current implementation at least)
1039 defined by objects. The mapping of encoding name to object is via the
1042 The values of the hash can currently be either strings or objects.
1043 The string form may go away in the future. The string form occurs
1044 when C<encodings()> has scanned C<@INC> for loadable encodings but has
1045 not actually loaded the encoding in question. This is because the
1046 current "loading" process is all Perl and a bit slow.
1048 Once an encoding is loaded then value of the hash is object which
1049 implements the encoding. The object should provide the following
1056 Should return the string representing the canonical name of the encoding.
1058 =item -E<gt>new_sequence
1060 This is a placeholder for encodings with state. It should return an
1061 object which implements this interface, all current implementations
1062 return the original object.
1064 =item -E<gt>encode($string,$check)
1066 Should return the octet sequence representing I<$string>. If I<$check>
1067 is true it should modify I<$string> in place to remove the converted
1068 part (i.e. the whole string unless there is an error). If an error
1069 occurs it should return the octet sequence for the fragment of string
1070 that has been converted, and modify $string in-place to remove the
1071 converted part leaving it starting with the problem fragment.
1073 If check is is false then C<encode> should make a "best effort" to
1074 convert the string - for example by using a replacement character.
1076 =item -E<gt>decode($octets,$check)
1078 Should return the string that I<$octets> represents. If I<$check> is
1079 true it should modify I<$octets> in place to remove the converted part
1080 (i.e. the whole sequence unless there is an error). If an error
1081 occurs it should return the fragment of string that has been
1082 converted, and modify $octets in-place to remove the converted part
1083 leaving it starting with the problem fragment.
1085 If check is is false then C<decode> should make a "best effort" to
1086 convert the string - for example by using Unicode's "\x{FFFD}" as a
1087 replacement character.
1091 It should be noted that the check behaviour is different from the
1092 outer public API. The logic is that the "unchecked" case is useful
1093 when encoding is part of a stream which may be reporting errors
1094 (e.g. STDERR). In such cases it is desirable to get everything
1095 through somehow without causing additional errors which obscure the
1096 original one. Also the encoding is best placed to know what the
1097 correct replacement character is, so if that is the desired behaviour
1098 then letting low level code do it is the most efficient.
1100 In contrast if check is true, the scheme above allows the encoding to
1101 do as much as it can and tell layer above how much that was. What is
1102 lacking at present is a mechanism to report what went wrong. The most
1103 likely interface will be an additional method call to the object, or
1104 perhaps (to avoid forcing per-stream objects on otherwise stateless
1105 encodings) and additional parameter.
1107 It is also highly desirable that encoding classes inherit from
1108 C<Encode::Encoding> as a base class. This allows that class to define
1109 additional behaviour for all encoding objects. For example built in
1110 Unicode, UCS-2 and UTF-8 classes use :
1112 package Encode::MyEncoding;
1113 use base qw(Encode::Encoding);
1115 __PACKAGE__->Define(qw(myCanonical myAlias));
1117 To create an object with bless {Name => ...},$class, and call
1118 define_encoding. They inherit their C<name> method from
1119 C<Encode::Encoding>.
1121 =head2 Compiled Encodings
1123 F<Encode.xs> provides a class C<Encode::XS> which provides the
1124 interface described above. It calls a generic octet-sequence to
1125 octet-sequence "engine" that is driven by tables (defined in
1126 F<encengine.c>). The same engine is used for both encode and
1127 decode. C<Encode:XS>'s C<encode> forces Perl's characters to their
1128 UTF-8 form and then treats them as just another multibyte
1129 encoding. C<Encode:XS>'s C<decode> transforms the sequence and then
1130 turns the UTF-8-ness flag as that is the form that the tables are
1131 defined to produce. For details of the engine see the comments in
1134 The tables are produced by the Perl script F<compile> (the name needs
1135 to change so we can eventually install it somewhere). F<compile> can
1136 currently read two formats:
1142 This is a coined format used by Tcl. It is documented in
1143 Encode/EncodeFormat.pod.
1147 This is the semi-standard format used by IBM's ICU package.
1151 F<compile> can write the following forms:
1157 See above - the F<Encode/*.ucm> files provided with the distribution have
1158 been created from the original Tcl .enc files using this approach.
1162 Produces tables as C data structures - this is used to build in encodings
1163 into F<Encode.so>/F<Encode.dll>.
1167 In theory this allows encodings to be stand-alone loadable Perl
1168 extensions. The process has not yet been tested. The plan is to use
1169 this approach for large East Asian encodings.
1173 The set of encodings built-in to F<Encode.so>/F<Encode.dll> is
1174 determined by F<Makefile.PL>. The current set is as follows:
1178 =item ascii and iso-8859-*
1180 That is all the common 8-bit "western" encodings.
1182 =item IBM-1047 and two other variants of EBCDIC.
1184 These are the same variants that are supported by EBCDIC Perl as
1185 "native" encodings. They are included to prove "reversibility" of
1186 some constructs in EBCDIC Perl.
1188 =item symbol and dingbats as used by Tk on X11.
1190 (The reason Encode got started was to support Perl/Tk.)
1194 That set is rather ad hoc and has been driven by the needs of the
1195 tests rather than the needs of typical applications. It is likely
1200 L<perlunicode>, L<perlebcdic>, L<perlfunc/open>, L<PerlIO>, L<encoding>