bytes.3

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

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.\" ========================================================================
.\"
.IX Title "bytes 3"
.TH bytes 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.SH "NAME"
bytes \- Perl pragma to force byte semantics rather than character semantics
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 8
\&    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;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \f(CW\*(C`use bytes\*(C'\fR pragma disables character semantics for the rest of the
lexical scope in which it appears.  \f(CW\*(C`no bytes\*(C'\fR can be used to reverse
the effect of \f(CW\*(C`use bytes\*(C'\fR within the current lexical scope.
.PP
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 \f(CW\*(C`use bytes\*(C'\fR is in
effect, the encoding is temporarily ignored, and each string is treated
as a series of bytes.
.PP
As an example, when Perl sees \f(CW\*(C`$x = chr(400)\*(C'\fR, it encodes the character
in \s-1UTF\-8\s0 and stores it in \f(CW$x\fR. Then it is marked as character data, so,
for instance, \f(CW\*(C`length $x\*(C'\fR returns \f(CW1\fR. However, in the scope of the
\&\f(CW\*(C`bytes\*(C'\fR pragma, \f(CW$x\fR is treated as a series of bytes \- the bytes that make
up the \s-1UTF8\s0 encoding \- and \f(CW\*(C`length $x\*(C'\fR returns \f(CW2\fR:
.PP
.Vb 8
\&    $x = chr(400);
\&    print "Length is ", length $x, "\en";     # "Length is 1"
\&    printf "Contents are %vd\en", $x;         # "Contents are 400"
\&    { 
\&        use bytes; # or "require bytes; bytes::length()"
\&        print "Length is ", length $x, "\en"; # "Length is 2"
\&        printf "Contents are %vd\en", $x;     # "Contents are 198.144"
\&    }
.Ve
.PP
\&\fIchr()\fR, \fIord()\fR, \fIsubstr()\fR, \fIindex()\fR and \fIrindex()\fR behave similarly.
.PP
For more on the implications and differences between character
semantics and byte semantics, see perluniintro and perlunicode.
.SH "LIMITATIONS"
.IX Header "LIMITATIONS"
\&\fIbytes::substr()\fR does not work as an \fIlvalue()\fR.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
perluniintro, perlunicode, utf8