man Unicode::String (3): String of Unicode characters (UTF-16BE)

SYNOPSIS

use Unicode::String qw(utf8 latin1 utf16be);
$u = utf8("string");
$u = latin1("string");
$u = utf16be("\0s\0t\0r\0i\0n\0g");
print $u->utf32be; # 4 byte characters
print $u->utf16le; # 2 byte characters + surrogates
print $u->utf8; # 1-4 byte characters

DESCRIPTION

A "Unicode::String" object represents a sequence of Unicode characters. Methods are provided to convert between various external formats (encodings) and "Unicode::String" objects, and methods are provided for common string manipulations.

The functions utf32be(), utf32le(), utf16be(), utf16le(), utf8(), utf7(), latin1(), uhex(), uchr() can be imported from the "Unicode::String" module and will work as constructors initializing strings of the corresponding encoding.

The "Unicode::String" objects overload various operators, which means that they in most cases can be treated like plain strings.

Internally a "Unicode::String" object is represented by a string of 2 byte numbers in network byte order (big-endian). This representation is not visible by the API provided, but it might be useful to know in order to predict the efficiency of the provided methods.

METHODS

Class methods

The following class methods are available:

Unicode::String->stringify_as

Unicode::String->stringify_as( $enc )

This method is used to specify which encoding will be used when "Unicode::String" objects are implicitly converted to and from plain strings.

If an argument is provided it sets the current encoding. The argument should have one of the following: ``ucs4'', ``utf32'', ``utf32be'', ``utf32le'', ``ucs2'', ``utf16'', ``utf16be'', ``utf16le'', ``utf8'', ``utf7'', ``latin1'' or ``hex''. The default is ``utf8''.

The stringify_as() method returns a reference to the current encoding function.

$us = Unicode::String->new

$us = Unicode::String->new( $initial_value )

This is the object constructor. Without argument, it creates an empty "Unicode::String" object. If an $initial_value argument is given, it is decoded according to the specified stringify_as() encoding, UTF-8 by default.

In general it is recommended to import and use one of the encoding specific constructor functions instead of invoking this method.

Encoding methods

These methods get or set the value of the "Unicode::String" object by passing strings in the corresponding encoding. If a new value is passed as argument it will set the value of the "Unicode::String", and the previous value is returned. If no argument is passed then the current value is returned.

To illustrate the encodings we show how the 2 character sample string of ``µm'' (micro meter) is encoded for each one.

$us->utf32be

$us->utf32be( $newval )

The string passed should be in the UTF-32 encoding with bytes in big endian order. The sample ``µm'' is ``\0\0\0\xB5\0\0\0m'' in this encoding.

Alternative names for this method are utf32() and ucs4().

$us->utf32le

$us->utf32le( $newval )

The string passed should be in the UTF-32 encoding with bytes in little endian order. The sample ``µm'' is is ``\xB5\0\0\0m\0\0\0'' in this encoding.

$us->utf16be

$us->utf16be( $newval )

The string passed should be in the UTF-16 encoding with bytes in big endian order. The sample ``µm'' is ``\0\xB5\0m'' in this encoding.

Alternative names for this method are utf16() and ucs2().

If the string passed to utf16be() starts with the Unicode byte order mark in little endian order, the result is as if utf16le() was called instead.

$us->utf16le

$us->utf16le( $newval )

The string passed should be in the UTF-16 encoding with bytes in little endian order. The sample ``µm'' is is ``\xB5\0m\0'' in this encoding. This is the encoding used by the Microsoft Windows API.

If the string passed to utf16le() starts with the Unicode byte order mark in big endian order, the result is as if utf16le() was called instead.

$us->utf8

$us->utf8( $newval )

The string passed should be in the UTF-8 encoding. The sample ``µm'' is ``\xC2\xB5m'' in this encoding.

$us->utf7

$us->utf7( $newval )

The string passed should be in the UTF-7 encoding. The sample ``µm'' is ``+ALU-m'' in this encoding.

The UTF-7 encoding only use plain US-ASCII characters for the encoding. This makes it safe for transport through 8-bit stripping protocols. Characters outside the US-ASCII range are base64-encoded and '+' is used as an escape character. The UTF-7 encoding is described in RFC 1642.

If the (global) variable $Unicode::String::UTF7_OPTIONAL_DIRECT_CHARS is TRUE, then a wider range of characters are encoded as themselves. It is even TRUE by default. The characters affected by this are:

   ! " # $ % & * ; < = > @ [ ] ^ _ ` { | }

$us->latin1

$us->latin1( $newval )

The string passed should be in the ISO-8859-1 encoding. The sample ``µm'' is ``\xB5m'' in this encoding.

Characters outside the ``\x00'' .. ``\xFF'' range are simply removed from the return value of the latin1() method. If you want more control over the mapping from Unicode to ISO-8859-1, use the "Unicode::Map8" class. This is also the way to deal with other 8-bit character sets.

$us->hex

$us->hex( $newval )

The string passed should be plain ASCII where each Unicode character is represented by the ``U+XXXX'' string and separated by a single space character. The ``U+'' prefix is optional when setting the value. The sample ``µm'' is ``U+00b5 U+006d'' in this encoding.

String Operations

The following methods are available:

$us->as_string

Converts a "Unicode::String" to a plain string according to the setting of stringify_as(). The default stringify_as() encoding is ``utf8''.

$us->as_num

Converts a "Unicode::String" to a number. Currently only the digits in the range 0x30 .. 0x39 are recognized. The plan is to eventually support all Unicode digit characters.

$us->as_bool

Converts a "Unicode::String" to a boolean value. Only the empty string is FALSE. A string consisting of only the character U+0030 is considered TRUE, even if Perl consider ``0'' to be FALSE.

$us->repeat( $count )

Returns a new "Unicode::String" where the content of $us is repeated $count times. This operation is also overloaded as:

  $us x $count

$us->concat( $other_string )

Concatenates the string $us and the string $other_string. If $other_string is not an "Unicode::String" object, then it is first passed to the Unicode::String->new constructor function. This operation is also overloaded as:

  $us . $other_string

$us->append( $other_string )

Appends the string $other_string to the value of $us. If $other_string is not an "Unicode::String" object, then it is first passed to the Unicode::String->new constructor function. This operation is also overloaded as:

  $us .= $other_string

$us->copy

Returns a copy of the current "Unicode::String" object. This operation is overloaded as the assignment operator.

$us->length

Returns the length of the "Unicode::String". Surrogate pairs are still counted as 2.

$us->byteswap

This method will swap the bytes in the internal representation of the "Unicode::String" object.

Unicode reserve the character U+FEFF character as a byte order mark. This works because the swapped character, U+FFFE, is reserved to not be valid. For strings that have the byte order mark as the first character, we can guaranty to get the byte order right with the following code:

   $ustr->byteswap if $ustr->ord == 0xFFFE;

$us->unpack

Returns a list of integers each representing an UCS-2 character code.

$us->pack( @uchr )

Sets the value of $us as a sequence of UCS-2 characters with the characters codes given as parameter.

$us->ord

Returns the character code of the first character in $us. The ord() method deals with surrogate pairs, which gives us a result-range of 0x0 .. 0x10FFFF. If the $us string is empty, undef is returned.

$us->chr( $code )

Sets the value of $us to be a string containing the character assigned code $code. The argument $code must be an integer in the range 0x0 .. 0x10FFFF. If the code is greater than 0xFFFF then a surrogate pair created.

$us->name

In scalar context returns the official Unicode name of the first character in $us. In array context returns the name of all characters in $us. Also see Unicode::CharName.

$us->substr( $offset )

$us->substr( $offset, $length )

$us->substr( $offset, $length, $subst )

Returns a sub-string of $us. Works similar to the builtin substr() function.

$us->index( $other )

$us->index( $other, $pos )

Locates the position of $other within $us, possibly starting the search at position $pos.

$us->chop

Chops off the last character of $us and returns it (as a "Unicode::String" object).

FUNCTIONS

The following functions are provided. None of these are exported by default.

byteswap2( $str, ... ): This function will swap 2 and 2 bytes in the strings passed as arguments. If this function is called in void context, then it will modify its arguments in-place. Otherwise, the swapped strings are returned.
byteswap4( $str, ... ): The byteswap4 function works similar to byteswap2, but will reverse the order of 4 and 4 bytes.
latin1( $str )
utf7( $str )
utf8( $str )
utf16le( $str )
utf16be( $str )
utf32le( $str )
utf32be( $str ): Constructor functions for the various Unicode encodings. These return new "Unicode::String" objects. The provided argument should be encoded correspondingly.
uhex( $str ): Constructs a new "Unicode::String" object from a string of hex values. See hex() method above for description of the format.
uchar( $num ): Constructs a new one character "Unicode::String" object from a Unicode character code. This works similar to perl's builtin chr() function.

COPYRIGHT

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

POD ERRORS

Hey! The above document had some coding errors, which are explained below:

Around line 600:: Non-ASCII character seen before =encoding in '``µm'''. Assuming ISO8859-1