encoding.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 "encoding 3"
.TH encoding 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH "NAME"
encoding \- allows you to write your script in non\-ascii or non\-utf8
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&  use encoding "greek";  # Perl like Greek to you?
\&  use encoding "euc\-jp"; # Jperl!
\&
\&  # or you can even do this if your shell supports your native encoding
\&
\&  perl \-Mencoding=latin2 \-e \*(Aq...\*(Aq # Feeling centrally European?
\&  perl \-Mencoding=euc\-kr \-e \*(Aq...\*(Aq # Or Korean?
\&
\&  # more control
\&
\&  # A simple euc\-cn => utf\-8 converter
\&  use encoding "euc\-cn", STDOUT => "utf8";  while(<>){print};
\&
\&  # "no encoding;" supported (but not scoped!)
\&  no encoding;
\&
\&  # an alternate way, Filter
\&  use encoding "euc\-jp", Filter=>1;
\&  # now you can use kanji identifiers \-\- in euc\-jp!
\&
\&  # switch on locale \-
\&  # note that this probably means that unless you have a complete control
\&  # over the environments the application is ever going to be run, you should
\&  # NOT use the feature of encoding pragma allowing you to write your script
\&  # in any recognized encoding because changing locale settings will wreck
\&  # the script; you can of course still use the other features of the pragma.
\&  use encoding \*(Aq:locale\*(Aq;
.Ve
.SH "ABSTRACT"
.IX Header "ABSTRACT"
Let's start with a bit of history: Perl 5.6.0 introduced Unicode
support.  You could apply \f(CW\*(C`substr()\*(C'\fR and regexes even to complex \s-1CJK\s0
characters \*(-- so long as the script was written in \s-1UTF\-8\s0.  But back
then, text editors that supported \s-1UTF\-8\s0 were still rare and many users
instead chose to write scripts in legacy encodings, giving up a whole
new feature of Perl 5.6.
.PP
Rewind to the future: starting from perl 5.8.0 with the \fBencoding\fR
pragma, you can write your script in any encoding you like (so long
as the \f(CW\*(C`Encode\*(C'\fR module supports it) and still enjoy Unicode support.
This pragma achieves that by doing the following:
.IP "\(bu" 4
Internally converts all literals (\f(CW\*(C`q//,qq//,qr//,qw///, qx//\*(C'\fR) from
the encoding specified to utf8.  In Perl 5.8.1 and later, literals in
\&\f(CW\*(C`tr///\*(C'\fR and \f(CW\*(C`DATA\*(C'\fR pseudo-filehandle are also converted.
.IP "\(bu" 4
Changing PerlIO layers of \f(CW\*(C`STDIN\*(C'\fR and \f(CW\*(C`STDOUT\*(C'\fR to the encoding
 specified.
.Sh "Literal Conversions"
.IX Subsection "Literal Conversions"
You can write code in EUC-JP as follows:
.PP
.Vb 3
\&  my $Rakuda = "\exF1\exD1\exF1\exCC"; # Camel in Kanji
\&               #<\-char\-><\-char\->   # 4 octets
\&  s/\ebCamel\eb/$Rakuda/;
.Ve
.PP
And with \f(CW\*(C`use encoding "euc\-jp"\*(C'\fR in effect, it is the same thing as
the code in \s-1UTF\-8:\s0
.PP
.Vb 2
\&  my $Rakuda = "\ex{99F1}\ex{99DD}"; # two Unicode Characters
\&  s/\ebCamel\eb/$Rakuda/;
.Ve
.ie n .Sh "PerlIO layers for ""STD(IN|OUT)"""
.el .Sh "PerlIO layers for \f(CWSTD(IN|OUT)\fP"
.IX Subsection "PerlIO layers for STD(IN|OUT)"
The \fBencoding\fR pragma also modifies the filehandle layers of
\&\s-1STDIN\s0 and \s-1STDOUT\s0 to the specified encoding.  Therefore,
.PP
.Vb 5
\&  use encoding "euc\-jp";
\&  my $message = "Camel is the symbol of perl.\en";
\&  my $Rakuda = "\exF1\exD1\exF1\exCC"; # Camel in Kanji
\&  $message =~ s/\ebCamel\eb/$Rakuda/;
\&  print $message;
.Ve
.PP
Will print \*(L"\exF1\exD1\exF1\exCC is the symbol of perl.\en\*(R",
not \*(L"\ex{99F1}\ex{99DD} is the symbol of perl.\en\*(R".
.PP
You can override this by giving extra arguments; see below.
.Sh "Implicit upgrading for byte strings"
.IX Subsection "Implicit upgrading for byte strings"
By default, if strings operating under byte semantics and strings
with Unicode character data are concatenated, the new string will
be created by decoding the byte strings as \fI\s-1ISO\s0 8859\-1 (Latin\-1)\fR.
.PP
The \fBencoding\fR pragma changes this to use the specified encoding
instead.  For example:
.PP
.Vb 5
\&    use encoding \*(Aqutf8\*(Aq;
\&    my $string = chr(20000); # a Unicode string
\&    utf8::encode($string);   # now it\*(Aqs a UTF\-8 encoded byte string
\&    # concatenate with another Unicode string
\&    print length($string . chr(20000));
.Ve
.PP
Will print \f(CW2\fR, because \f(CW$string\fR is upgraded as \s-1UTF\-8\s0.  Without
\&\f(CW\*(C`use encoding \*(Aqutf8\*(Aq;\*(C'\fR, it will print \f(CW4\fR instead, since \f(CW$string\fR
is three octets when interpreted as Latin\-1.
.Sh "Side effects"
.IX Subsection "Side effects"
If the \f(CW\*(C`encoding\*(C'\fR pragma is in scope then the lengths returned are
calculated from the length of \f(CW$/\fR in Unicode characters, which is not
always the same as the length of \f(CW$/\fR in the native encoding.
.PP
This pragma affects utf8::upgrade, but not utf8::downgrade.
.Sh "Side effects"
.IX Subsection "Side effects"
If the \f(CW\*(C`encoding\*(C'\fR pragma is in scope then the lengths returned are
calculated from the length of \f(CW$/\fR in Unicode characters, which is not
always the same as the length of \f(CW$/\fR in the native encoding.
.PP
This pragma affects utf8::upgrade, but not utf8::downgrade.
.Sh "Side effects"
.IX Subsection "Side effects"
If the \f(CW\*(C`encoding\*(C'\fR pragma is in scope then the lengths returned are
calculated from the length of \f(CW$/\fR in Unicode characters, which is not
always the same as the length of \f(CW$/\fR in the native encoding.
.PP
This pragma affects utf8::upgrade, but not utf8::downgrade.
.SH "FEATURES THAT REQUIRE 5.8.1"
.IX Header "FEATURES THAT REQUIRE 5.8.1"
Some of the features offered by this pragma requires perl 5.8.1.  Most
of these are done by Inaba Hiroto.  Any other features and changes
are good for 5.8.0.
.ie n .IP """NON-EUC"" doublebyte encodings" 4
.el .IP "``NON-EUC'' doublebyte encodings" 4
.IX Item "NON-EUC doublebyte encodings"
Because perl needs to parse script before applying this pragma, such
encodings as Shift_JIS and Big\-5 that may contain '\e' (\s-1BACKSLASH\s0;
\&\ex5c) in the second byte fails because the second byte may
accidentally escape the quoting character that follows.  Perl 5.8.1
or later fixes this problem.
.IP "tr//" 4
.IX Item "tr//"
\&\f(CW\*(C`tr//\*(C'\fR was overlooked by Perl 5 porters when they released perl 5.8.0
See the section below for details.
.IP "\s-1DATA\s0 pseudo-filehandle" 4
.IX Item "DATA pseudo-filehandle"
Another feature that was overlooked was \f(CW\*(C`DATA\*(C'\fR.
.SH "USAGE"
.IX Header "USAGE"
.IP "use encoding [\fI\s-1ENCNAME\s0\fR] ;" 4
.IX Item "use encoding [ENCNAME] ;"
Sets the script encoding to \fI\s-1ENCNAME\s0\fR.  And unless ${^UNICODE} 
exists and non-zero, PerlIO layers of \s-1STDIN\s0 and \s-1STDOUT\s0 are set to
":encoding(\fI\s-1ENCNAME\s0\fR)".
.Sp