ext::Encode::EncoPerlpProgrammers Referencext::Encode::Encode(3p)NAMEEncode - 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 plat-
forms 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 charac-
ters 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".
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TERMINOLOGY
+ character: a character in the range 0..(2**32-1) (or
more). (What Perl's strings are made of.)
+ byte: a character in the range 0..255 (A special case of a
Perl character.)
+ 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 for-
mat 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 contains completely
valid utf8 string. See "The UTF-8 flag" below.
If the $string is "undef" then "undef" is returned.
$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 canoni-
cal name or an alias. For encoding names and aliases, see
"Defining Aliases". For CHECK, see "Handling Malformed
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 for $string is
on unless $octets entirely consists of ASCII data (or
EBCDIC on EBCDIC machines). See "The UTF-8 flag" below.
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If the $string is "undef" then "undef" is returned.
[$length =] from_to($octets, FROM_ENC, TO_ENC [, CHECK])
Converts in-place data between two encodings. The data in
$octets must be encoded as octets and not as characters in
Perl's internal format. For example, to convert ISO-8859-1
data to Microsoft's CP1250 encoding:
from_to($octets, "iso-8859-1", "cp1250");
and to convert it back:
from_to($octets, "cp1250", "iso-8859-1");
Note that because the conversion happens in place, the
data to be converted cannot be a string constant; it must
be a scalar variable.
from_to() returns the length of the converted string in
octets on success, undef on error.
CAVEAT: The following operations look the same but are not
quite so;
from_to($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 represen-
tation so this function cannot fail.
$string = decode_utf8($octets [, CHECK]);
equivalent to "$string = decode("utf8", $octets [,
CHECK])". The sequence of octets represented by $octets is
decoded from UTF-8 into a sequence of logical characters.
Not all sequences of octets form valid UTF-8 encodings, so
it is possible for this call to fail. For CHECK, see
"Handling Malformed Data".
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Listing available encodings
use Encode;
@list = Encode->encodings();
Returns a list of the canonical names of the available
encodings that are loaded. To get a list of all available
encodings including the ones that are not loaded yet, say
@all_encodings = Encode->encodings(":all");
Or you can give the name of a specific module.
@with_jp = Encode->encodings("Encode::JP");
When "::" is not in the name, "Encode::" is assumed.
@ebcdic = Encode->encodings("EBCDIC");
To find out in detail which encodings are supported by this
package, see Encode::Supported.
Defining Aliases
To add a new alias to a given encoding, use:
use Encode;
use Encode::Alias;
define_alias(newName => ENCODING);
After that, newName can be used as an alias for ENCODING.
ENCODING may be either the name of an encoding or an encod-
ing object
But before you do so, make sure the alias is nonexistent
with "resolve_alias()", which returns the canonical name
thereof. i.e.
Encode::resolve_alias("latin1") eq "iso-8859-1" # true
Encode::resolve_alias("iso-8859-12") # false; nonexistent
Encode::resolve_alias($name) eq $name # true if $name is canonical
resolve_alias() does not need "use Encode::Alias"; it can be
exported via "use Encodeqw(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 identi-
cal in their functionality.
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# 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 Encodeqw(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 optional CHECK argument tells Encode what to do when it
encounters malformed data. Without CHECK,
Encode::FB_DEFAULT ( == 0 ) is assumed.
As of version 2.12 Encode supports coderef values for CHECK.
See below.
NOTE: Not all encoding support this feature
Some encodings ignore CHECK argument. For example,
Encode::Unicode ignores CHECK and it always croaks on
error.
Now here is the list of CHECK values available
CHECK = Encode::FB_DEFAULT ( == 0)
If CHECK is 0, (en|de)code will put a substitution charac-
ter in place of a malformed character. When you encode,
<subchar> will be used. When you decode 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
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should trap the error with eval{} unless you really want
to let it die.
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 character
sequences, (i.e. you are reading with a fixed-width
buffer). Here is a sample code that does exactly this:
my $buffer = ''; my $string = '';
while(read $fh, $buffer, 256, length($buffer)){
$string .= decode($encoding, $buffer, Encode::FB_QUIET);
# $buffer 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 "&#NNN;" where NNN is a
decimal number and XML uses "&#xHHHH;" where HHHH is the
hexadecimal number.
In Encode 2.10 or later, "LEAVE_SRC" is also implied.
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)".
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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 X
PERLQQ 0x0100 X
HTMLCREF 0x0200
XMLCREF 0x0400
coderef for CHECK
As of Encode 2.12 CHECK can also be a code reference which
takes the ord value of unmapped caharacter as an argument
and returns a string that represents the fallback character.
For instance,
$ascii = encode("ascii", $utf8, sub{ sprintf "<U+%04X>", shift });
Acts like FB_PERLQQ but <U+XXXX> is used instead of
\x{XXXX}.
Defining Encodings
To define a new encoding, use:
use Encodeqw(define_encoding);
define_encoding($object, 'canonicalName' [, alias...]);
canonicalName will be associated with $object. The object
should provide the interface described in Encode::Encoding.
If more than two arguments are provided then additional
arguments are taken as aliases for $object.
See Encode::Encoding for more details.
The UTF-8 flag
Before the introduction of utf8 support in perl, The "eq"
operator just compared the strings represented by two
scalars. Beginning with perl 5.8, "eq" compares two strings
with simultaneous consideration of the utf8 flag. To explain
why we made it so, I will quote page 402 of "Programming
Perl, 3rd ed."
Goal #1:
Old byte-oriented programs should not spontaneously break
on the old byte-oriented data they used to work on.
Goal #2:
Old byte-oriented programs should magically start working
on the new character-oriented data when appropriate.
Goal #3:
Programs should run just as fast in the new character-
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oriented mode as in the old byte-oriented mode.
Goal #4:
Perl should remain one language, rather than forking into
a byte-oriented Perl and a character-oriented Perl.
Back when "Programming Perl, 3rd ed." was written, not even
Perl 5.6.0 was born and many features documented in the book
remained unimplemented for a long time. Perl 5.8 corrected
this and the introduction of the UTF-8 flag is one of them.
You can think of this perl notion as of a byte-oriented mode
(utf8 flag off) and a character-oriented mode (utf8 flag
on).
Here is how Encode takes care of the utf8 flag.
+ When you encode, the resulting utf8 flag is always off.
+ When you decode, the resulting utf8 flag is on unless you
can unambiguously represent data. Here is the definition
of dis-ambiguity.
After "$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 assume 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
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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 indicating 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 UTF-8 flag
(so please don't treat the return value as indicating suc-
cess or failure), or "undef" if STRING is not a string.
UTF-8 vs. utf8
....We now view strings not as sequences of bytes, but as sequences
of numbers in the range 0 .. 2**32-1 (or in the case of 64-bit
computers, 0 .. 2**64-1) -- Programming Perl, 3rd ed.
That has been the perl's notion of UTF-8 but official UTF-8
is more strict; Its ranges is much narrower (0 .. 10FFFF),
some sequences are not allowed (i.e. Those used in the sur-
rogate pair, 0xFFFE, et al).
Now that is overruled by Larry Wall himself.
From: Larry Wall <larry@wall.org>
Date: December 04, 2004 11:51:58 JST
To: perl-unicode@perl.org
Subject: Re: Make Encode.pm support the real UTF-8
Message-Id: <20041204025158.GA28754@wall.org>
On Fri, Dec 03, 2004 at 10:12:12PM +0000, Tim Bunce wrote:
: I've no problem with 'utf8' being perl's unrestricted uft8 encoding,
: but "UTF-8" is the name of the standard and should give the
: corresponding behaviour.
For what it's worth, that's how I've always kept them straight in my
head.
Also for what it's worth, Perl 6 will mostly default to strict but
make it easy to switch back to lax.
Larry
Do you copy? As of Perl 5.8.7, UTF-8 means strict, official
UTF-8 while utf8 means liberal, lax, version thereof. And
Encode version 2.10 or later thus groks the difference
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between "UTF-8" and C"utf8".
encode("utf8", "\x{FFFF_FFFF}", 1); # okay
encode("UTF-8", "\x{FFFF_FFFF}", 1); # croaks
"UTF-8" in Encode is actually a canonical name for
"utf-8-strict". Yes, the hyphen between "UTF" and "8" is
important. Without it Encode goes "liberal"
find_encoding("UTF-8")->name # is 'utf-8-strict'
find_encoding("utf-8")->name # ditto. names are case insensitive
find_encoding("utf8")->name # ditto. "_" are treated as "-"
find_encoding("UTF8")->name # is 'utf8'.
SEE ALSO
Encode::Encoding, Encode::Supported, Encode::PerlIO, encod-
ing, perlebcdic, "open" in perlfunc, perlunicode, utf8, the
Perl Unicode Mailing List <perl-unicode@perl.org>
MAINTAINER
This project was originated by Nick Ing-Simmons and later
maintained by Dan Kogai <dankogai@dan.co.jp>. See AUTHORS
for a full list of people involved. For any questions, use
<perl-unicode@perl.org> so we can all share.
perl v5.8.8 2005-02-05 10
