unixdev.net


Switch to SpeakEasy.net DSL

The Modular Manual Browser

Home Page
Manual: (OpenBSD-3.6)
Page:
Section:
Apropos / Subsearch:
optional field



ext::Encode::EncoPerlpProgrammers Referencext::Encode::Encode(3p)


NAME
       Encode - character encodings

SYNOPSIS
           use Encode;

       Table of Contents

       Encode consists of a collection of modules whose details
       are too big to fit in one document.  This POD itself
       explains the top-level APIs and general topics at a
       glance.  For other topics and more details, see the PODs
       below:

         Name                          Description
         --------------------------------------------------------
         Encode::Alias         Alias definitions to encodings
         Encode::Encoding      Encode Implementation Base Class
         Encode::Supported     List of Supported Encodings
         Encode::CN            Simplified Chinese Encodings
         Encode::JP            Japanese Encodings
         Encode::KR            Korean Encodings
         Encode::TW            Traditional Chinese Encodings
         --------------------------------------------------------

DESCRIPTION
       The "Encode" module provides the interfaces between Perl's
       strings and the rest of the system.  Perl strings are
       sequences of characters.

       The repertoire of characters that Perl can represent is at
       least that defined by the Unicode Consortium. On most
       platforms the ordinal values of the characters (as
       returned by "ord(ch)") is the "Unicode codepoint" for the
       character (the exceptions are those platforms where the
       legacy encoding is some variant of EBCDIC rather than a
       super-set of ASCII - see perlebcdic).

       Traditionally, computer data has been moved around in
       8-bit chunks often called "bytes". These chunks are also
       known as "octets" in networking standards. Perl is widely
       used to manipulate data of many types - not only strings
       of characters representing human or computer languages but
       also "binary" data being the machine's representation of
       numbers, pixels in an image - or just about anything.

       When Perl is processing "binary data", the programmer
       wants Perl to process "sequences of bytes". This is not a
       problem for Perl - as a byte has 256 possible values, it
       easily fits in Perl's much larger "logical character".







perl v5.8.5                 2002-11-06                          1





ext::Encode::EncoPerlpProgrammers Referencext::Encode::Encode(3p)


       TERMINOLOGY


       o character: a character in the range 0..(2**32-1) (or
         more).  (What Perl's strings are made of.)

       o byte: a character in the range 0..255 (A special case of
         a Perl character.)

       o octet: 8 bits of data, with ordinal values 0..255 (Term
         for bytes passed to or from a non-Perl context, e.g. a
         disk file.)

PERL ENCODING API
       $octets  = encode(ENCODING, $string [, CHECK])
         Encodes a string from Perl's internal form into ENCODING
         and returns a sequence of octets.  ENCODING can be
         either a canonical name or an alias.  For encoding names
         and aliases, see "Defining Aliases".  For CHECK, see
         "Handling Malformed Data".

         For example, to convert a string from Perl's internal
         format to iso-8859-1 (also known as Latin1),

           $octets = encode("iso-8859-1", $string);

         CAVEAT: When you run "$octets = encode("utf8",
         $string)", then $octets may not be equal to $string.
         Though they both contain the same data, the utf8 flag
         for $octets is always off.  When you encode anything,
         utf8 flag of the result is always off, even when it con-
         tains completely valid utf8 string. See "The UTF-8 flag"
         below.

         encode($valid_encoding, undef) is harmless but warns you
         for "Use of uninitialized value in subroutine entry".
         encode($valid_encoding, '') is harmless and warnless.

       $string = decode(ENCODING, $octets [, CHECK])
         Decodes a sequence of octets assumed to be in ENCODING
         into Perl's internal form and returns the resulting
         string.  As in encode(), ENCODING can be either a canon-
         ical name or an alias. For encoding names and aliases,
         see "Defining Aliases".  For CHECK, see "Handling Mal-
         formed Data".

         For example, to convert ISO-8859-1 data to a string in
         Perl's internal format:

           $string = decode("iso-8859-1", $octets);

         CAVEAT: When you run "$string = decode("utf8",
         $octets)", then $string may not be equal to $octets.
         Though they both contain the same data, the utf8 flag



perl v5.8.5                 2002-11-06                          2





ext::Encode::EncoPerlpProgrammers Referencext::Encode::Encode(3p)


         for $string is on unless $octets entirely consists of
         ASCII data (or EBCDIC on EBCDIC machines).  See "The
         UTF-8 flag" below.

         decode($valid_encoding, undef) is harmless but warns you
         for "Use of uninitialized value in subroutine entry".
         decode($valid_encoding, '') is harmless and warnless.

       [$length =] from_to($octets, FROM_ENC, TO_ENC [, CHECK])
         Converts in-place data between two encodings. The data
         in $octets must be encoded as octets and not as charac-
         ters in Perl's internal format. For example, to convert
         ISO-8859-1 data to Microsoft's CP1250 encoding:

           from_to($octets, "iso-8859-1", "cp1250");

         and to convert it back:

           from_to($octets, "cp1250", "iso-8859-1");

         Note that because the conversion happens in place, the
         data to be converted cannot be a string constant; it
         must be a scalar variable.

         from_to() returns the length of the converted string in
         octets on success, undef otherwise.

         CAVEAT: The following operations look the same but are
         not quite so;

           from_to($data, "iso-8859-1", "utf8"); #1
           $data = decode("iso-8859-1", $data);  #2

         Both #1 and #2 make $data consist of a completely valid
         UTF-8 string but only #2 turns utf8 flag on.  #1 is
         equivalent to

           $data = encode("utf8", decode("iso-8859-1", $data));

         See "The UTF-8 flag" below.

       $octets = encode_utf8($string);
         Equivalent to "$octets = encode("utf8", $string);" The
         characters that comprise $string are encoded in Perl's
         internal format and the result is returned as a sequence
         of octets. All possible characters have a UTF-8 repre-
         sentation so this function cannot fail.

       $string = decode_utf8($octets [, CHECK]);
         equivalent to "$string = decode("utf8", $octets [,
         CHECK])".  The sequence of octets represented by $octets
         is decoded from UTF-8 into a sequence of logical charac-
         ters. Not all sequences of octets form valid UTF-8
         encodings, so it is possible for this call to fail.  For



perl v5.8.5                 2002-11-06                          3





ext::Encode::EncoPerlpProgrammers Referencext::Encode::Encode(3p)


         CHECK, see "Handling Malformed Data".

       Listing available encodings

         use Encode;
         @list = Encode->encodings();

       Returns a list of the canonical names of the available
       encodings that are loaded.  To get a list of all available
       encodings including the ones that are not loaded yet, say

         @all_encodings = Encode->encodings(":all");

       Or you can give the name of a specific module.

         @with_jp = Encode->encodings("Encode::JP");

       When "::" is not in the name, "Encode::" is assumed.

         @ebcdic = Encode->encodings("EBCDIC");

       To find out in detail which encodings are supported by
       this package, see Encode::Supported.

       Defining Aliases

       To add a new alias to a given encoding, use:

         use Encode;
         use Encode::Alias;
         define_alias(newName => ENCODING);

       After that, newName can be used as an alias for ENCODING.
       ENCODING may be either the name of an encoding or an
       encoding object

       But before you do so, make sure the alias is nonexistent
       with "resolve_alias()", which returns the canonical name
       thereof.  i.e.

         Encode::resolve_alias("latin1") eq "iso-8859-1" # true
         Encode::resolve_alias("iso-8859-12")   # false; nonexistent
         Encode::resolve_alias($name) eq $name  # true if $name is canonical

       resolve_alias() does not need "use Encode::Alias"; it can
       be exported via "use Encode qw(resolve_alias)".

       See Encode::Alias for details.

Encoding via PerlIO
       If your perl supports PerlIO (which is the default), you
       can use a PerlIO layer to decode and encode directly via a
       filehandle.  The following two examples are totally iden-
       tical in their functionality.



perl v5.8.5                 2002-11-06                          4





ext::Encode::EncoPerlpProgrammers Referencext::Encode::Encode(3p)


         # via PerlIO
         open my $in,  "<:encoding(shiftjis)", $infile  or die;
         open my $out, ">:encoding(euc-jp)",   $outfile or die;
         while(<$in>){ print $out $_; }

         # via from_to
         open my $in,  "<", $infile  or die;
         open my $out, ">", $outfile or die;
         while(<$in>){
           from_to($_, "shiftjis", "euc-jp", 1);
           print $out $_;
         }

       Unfortunately, it may be that encodings are PerlIO-savvy.
       You can check if your encoding is supported by PerlIO by
       calling the "perlio_ok" method.

         Encode::perlio_ok("hz");             # False
         find_encoding("euc-cn")->perlio_ok;  # True where PerlIO is available

         use Encode qw(perlio_ok);            # exported upon request
         perlio_ok("euc-jp")

       Fortunately, all encodings that come with Encode core are
       PerlIO-savvy except for hz and ISO-2022-kr.  For gory
       details, see Encode::Encoding and Encode::PerlIO.

Handling Malformed Data
       The CHECK argument is used as follows.  When you omit it,
       the behaviour is the same as if you had passed a value of
       0 for CHECK.

       CHECK = Encode::FB_DEFAULT ( == 0)
         If CHECK is 0, (en|de)code will put a substitution char-
         acter in place of a malformed character.  For UCM-based
         encodings, <subchar> will be used.  For Unicode, the
         code point 0xFFFD is used.  If the data is supposed to
         be UTF-8, an optional lexical warning (category utf8) is
         given.

       CHECK = Encode::FB_CROAK ( == 1)
         If CHECK is 1, methods will die on error immediately
         with an error message.  Therefore, when CHECK is set to
         1,  you should trap the fatal error with eval{} unless
         you really want to let it die on error.

       CHECK = Encode::FB_QUIET
         If CHECK is set to Encode::FB_QUIET, (en|de)code will
         immediately return the portion of the data that has been
         processed so far when an error occurs. The data argument
         will be overwritten with everything after that point
         (that is, the unprocessed part of data).  This is handy
         when you have to call decode repeatedly in the case
         where your source data may contain partial multi-byte



perl v5.8.5                 2002-11-06                          5





ext::Encode::EncoPerlpProgrammers Referencext::Encode::Encode(3p)


         character sequences, for example because you are reading
         with a fixed-width buffer. Here is some sample code that
         does exactly this:

           my $data = ''; my $utf8 = '';
           while(defined(read $fh, $buffer, 256)){
             # buffer may end in a partial character so we append
             $data .= $buffer;
             $utf8 .= decode($encoding, $data, Encode::FB_QUIET);
             # $data now contains the unprocessed partial character
           }

       CHECK = Encode::FB_WARN
         This is the same as above, except that it warns on
         error.  Handy when you are debugging the mode above.

       perlqq mode (CHECK = Encode::FB_PERLQQ)
       HTML charref mode (CHECK = Encode::FB_HTMLCREF)
       XML charref mode (CHECK = Encode::FB_XMLCREF)
         For encodings that are implemented by Encode::XS, CHECK
         == Encode::FB_PERLQQ turns (en|de)code into "perlqq"
         fallback mode.

         When you decode, "\xHH" will be inserted for a malformed
         character, where HH is the hex representation of the
         octet  that could not be decoded to utf8.  And when you
         encode, "\x{HHHH}" will be inserted, where HHHH is the
         Unicode ID of the character that cannot be found in the
         character repertoire of the encoding.

         HTML/XML character reference modes are about the same,
         in place of "\x{HHHH}", HTML uses "&#NNNN"; where NNNN
         is a decimal digit and XML uses "&#xHHHH"; where HHHH is
         the hexadecimal digit.

       The bitmask
         These modes are actually set via a bitmask.  Here is how
         the FB_XX constants are laid out.  You can import the
         FB_XX constants via "use Encode qw(:fallbacks)"; you can
         import the generic bitmask constants via "use Encode
         qw(:fallback_all)".

                              FB_DEFAULT FB_CROAK FB_QUIET FB_WARN  FB_PERLQQ
          DIE_ON_ERR    0x0001             X
          WARN_ON_ERR   0x0002                               X
          RETURN_ON_ERR 0x0004                      X        X
          LEAVE_SRC     0x0008
          PERLQQ        0x0100                                        X
          HTMLCREF      0x0200
          XMLCREF       0x0400







perl v5.8.5                 2002-11-06                          6





ext::Encode::EncoPerlpProgrammers Referencext::Encode::Encode(3p)


       Unimplemented fallback schemes

       In the future, you will be able to use a code reference to
       a callback function for the value of CHECK but its API is
       still undecided.

       The fallback scheme does not work on EBCDIC platforms.

Defining Encodings
       To define a new encoding, use:

           use Encode qw(define_encoding);
           define_encoding($object, 'canonicalName' [, alias...]);

       canonicalName will be associated with $object.  The object
       should provide the interface described in Encode::Encod-
       ing.  If more than two arguments are provided then addi-
       tional arguments are taken as aliases for $object.

       See Encode::Encoding for more details.

The UTF-8 flag
       Before the introduction of utf8 support in perl, The "eq"
       operator just compared the strings represented by two
       scalars. Beginning with perl 5.8, "eq" compares two
       strings with simultaneous consideration of the utf8 flag.
       To explain why we made it so, I will quote page 402 of
       "Programming Perl, 3rd ed."

       Goal #1:
         Old byte-oriented programs should not spontaneously
         break on the old byte-oriented data they used to work
         on.

       Goal #2:
         Old byte-oriented programs should magically start work-
         ing on the new character-oriented data when appropriate.

       Goal #3:
         Programs should run just as fast in the new character-
         oriented mode as in the old byte-oriented mode.

       Goal #4:
         Perl should remain one language, rather than forking
         into a byte-oriented Perl and a character-oriented Perl.

       Back when "Programming Perl, 3rd ed." was written, not
       even Perl 5.6.0 was born and many features documented in
       the book remained unimplemented for a long time.  Perl 5.8
       corrected this and the introduction of the UTF-8 flag is
       one of them.  You can think of this perl notion as of a
       byte-oriented mode (utf8 flag off) and a character-ori-
       ented mode (utf8 flag on).




perl v5.8.5                 2002-11-06                          7





ext::Encode::EncoPerlpProgrammers Referencext::Encode::Encode(3p)


       Here is how Encode takes care of the utf8 flag.

       o When you encode, the resulting utf8 flag is always off.

       o When you decode, the resulting utf8 flag is on unless
         you can unambiguously represent data.  Here is the defi-
         nition of dis-ambiguity.

         After "$utf8 = decode('foo', $octet);",

           When $octet is...   The utf8 flag in $utf8 is
           ---------------------------------------------
           In ASCII only (or EBCDIC only)            OFF
           In ISO-8859-1                              ON
           In any other Encoding                      ON
           ---------------------------------------------

         As you see, there is one exception, In ASCII.  That way
         you can assue Goal #1.  And with Encode Goal #2 is
         assumed but you still have to be careful in such cases
         mentioned in CAVEAT paragraphs.

         This utf8 flag is not visible in perl scripts, exactly
         for the same reason you cannot (or you don't have to)
         see if a scalar contains a string, integer, or floating
         point number.   But you can still peek and poke these if
         you will.  See the section below.

       Messing with Perl's Internals

       The following API uses parts of Perl's internals in the
       current implementation.  As such, they are efficient but
       may change.

       is_utf8(STRING [, CHECK])
         [INTERNAL] Tests whether the UTF-8 flag is turned on in
         the STRING.  If CHECK is true, also checks the data in
         STRING for being well-formed UTF-8.  Returns true if
         successful, false otherwise.

         As of perl 5.8.1, utf8 also has utf8::is_utf8().

       _utf8_on(STRING)
         [INTERNAL] Turns on the UTF-8 flag in STRING.  The data
         in STRING is not checked for being well-formed UTF-8.
         Do not use unless you know that the STRING is well-
         formed UTF-8.  Returns the previous state of the UTF-8
         flag (so please don't treat the return value as indicat-
         ing success or failure), or "undef" if STRING is not a
         string.

       _utf8_off(STRING)
         [INTERNAL] Turns off the UTF-8 flag in STRING.  Do not
         use frivolously.  Returns the previous state of the



perl v5.8.5                 2002-11-06                          8





ext::Encode::EncoPerlpProgrammers Referencext::Encode::Encode(3p)


         UTF-8 flag (so please don't treat the return value as
         indicating success or failure), or "undef" if STRING is
         not a string.

SEE ALSO
       Encode::Encoding, Encode::Supported, Encode::PerlIO,
       encoding, perlebcdic, "open" in perlfunc, perlunicode,
       utf8, the Perl Unicode Mailing List <perl-uni-
       codeATperl.org>

MAINTAINER
       This project was originated by Nick Ing-Simmons and later
       maintained by Dan Kogai <dankogaiATdan.jp>.  See AUTHORS
       for a full list of people involved.  For any questions,
       use <perl-unicodeATperl.org> so we can all share.










































perl v5.8.5                 2002-11-06                          9