名前¶

bytes - 文字単位ではなくバイト単位の意味論を強制する Perl プラグマ

概要¶

    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;

説明¶

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. (TBT)

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. (TBT)

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: (TBT)

    $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. (TBT)

For more on the implications and differences between character semantics and byte semantics, see perluniintro and perlunicode. (TBT)

制限¶

bytes::substr() は lvalue() では動作しません。

SEE ALSO¶

perluniintro, perlunicode, utf8