NAME¶
bytes - Perl pragma to force byte semantics rather than character semantics
NOTICE¶
This pragma reflects early attempts to incorporate Unicode into perl and has
since been superseded. It breaks encapsulation (i.e. it exposes the innards of
how the perl executable currently happens to store a string), and use of this
module for anything other than debugging purposes is strongly discouraged. If
you feel that the functions here within might be useful for your application,
this possibly indicates a mismatch between your mental model of Perl Unicode
and the current reality. In that case, you may wish to read some of the perl
Unicode documentation: perluniintro, perlunitut, perlunifaq and perlunicode.
SYNOPSIS¶
use bytes;
... chr(...); # or bytes::chr
... index(...); # or bytes::index
... length(...); # or bytes::length
... ord(...); # or bytes::ord
... rindex(...); # or bytes::rindex
... substr(...); # or bytes::substr
no bytes;
DESCRIPTION¶
The "use bytes" pragma disables character semantics for the rest of
the lexical scope in which it appears. "no bytes" can be used to
reverse the effect of "use bytes" within the current lexical scope.
Perl normally assumes character semantics in the presence of character data
(i.e. data that has come from a source that has been marked as being of a
particular character encoding). When "use bytes" is in effect, the
encoding is temporarily ignored, and each string is treated as a series of
bytes.
As an example, when Perl sees "$x = chr(400)", it encodes the
character in UTF-8 and stores it in $x. Then it is marked as character data,
so, for instance, "length $x" returns 1. However, in the scope of
the "bytes" pragma, $x is treated as a series of bytes - the bytes
that make up the UTF8 encoding - and "length $x" returns 2:
$x = chr(400);
print "Length is ", length $x, "\n"; # "Length is 1"
printf "Contents are %vd\n", $x; # "Contents are 400"
{
use bytes; # or "require bytes; bytes::length()"
print "Length is ", length $x, "\n"; # "Length is 2"
printf "Contents are %vd\n", $x; # "Contents are 198.144"
}
chr(),
ord(),
substr(),
index() and
rindex()
behave similarly.
For more on the implications and differences between character semantics and
byte semantics, see perluniintro and perlunicode.
LIMITATIONS¶
bytes::substr() does not work as an
lvalue().
SEE ALSO¶
perluniintro, perlunicode, utf8