perlunifaq.1

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 "PERLUNIFAQ 1"
.TH PERLUNIFAQ 1 "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"
perlunifaq \- Perl Unicode FAQ
.SH "Q and A"
.IX Header "Q and A"
This is a list of questions and answers about Unicode in Perl, intended to be
read after perlunitut.
.Sh "perlunitut isn't really a Unicode tutorial, is it?"
.IX Subsection "perlunitut isn't really a Unicode tutorial, is it?"
No, and this isn't really a Unicode \s-1FAQ\s0.
.PP
Perl has an abstracted interface for all supported character encodings, so they
is actually a generic \f(CW\*(C`Encode\*(C'\fR tutorial and \f(CW\*(C`Encode\*(C'\fR \s-1FAQ\s0. But many people
think that Unicode is special and magical, and I didn't want to disappoint
them, so I decided to call the document a Unicode tutorial.
.Sh "What character encodings does Perl support?"
.IX Subsection "What character encodings does Perl support?"
To find out which character encodings your Perl supports, run:
.PP
.Vb 1
\&    perl \-MEncode \-le "print for Encode\->encodings(\*(Aq:all\*(Aq)"
.Ve
.Sh "Which version of perl should I use?"
.IX Subsection "Which version of perl should I use?"
Well, if you can, upgrade to the most recent, but certainly \f(CW5.8.1\fR or newer.
The tutorial and \s-1FAQ\s0 are based on the status quo as of \f(CW5.8.8\fR.
.PP
You should also check your modules, and upgrade them if necessary. For example,
HTML::Entities requires version >= 1.32 to function correctly, even though the
changelog is silent about this.
.Sh "What about binary data, like images?"
.IX Subsection "What about binary data, like images?"
Well, apart from a bare \f(CW\*(C`binmode $fh\*(C'\fR, you shouldn't treat them specially.
(The binmode is needed because otherwise Perl may convert line endings on Win32
systems.)
.PP
Be careful, though, to never combine text strings with binary strings. If you
need text in a binary stream, encode your text strings first using the
appropriate encoding, then join them with binary strings. See also: \*(L"What if I
don't encode?\*(R".
.Sh "When should I decode or encode?"
.IX Subsection "When should I decode or encode?"
Whenever you're communicating text with anything that is external to your perl
process, like a database, a text file, a socket, or another program. Even if
the thing you're communicating with is also written in Perl.
.Sh "What if I don't decode?"
.IX Subsection "What if I don't decode?"
Whenever your encoded, binary string is used together with a text string, Perl
will assume that your binary string was encoded with \s-1ISO\-8859\-1\s0, also known as
latin\-1. If it wasn't latin\-1, then your data is unpleasantly converted. For
example, if it was \s-1UTF\-8\s0, the individual bytes of multibyte characters are seen
as separate characters, and then again converted to \s-1UTF\-8\s0. Such double encoding
can be compared to double \s-1HTML\s0 encoding (\f(CW\*(C`&amp;gt;\*(C'\fR), or double \s-1URI\s0 encoding
(\f(CW%253E\fR).
.PP
This silent implicit decoding is known as \*(L"upgrading\*(R". That may sound
positive, but it's best to avoid it.
.Sh "What if I don't encode?"
.IX Subsection "What if I don't encode?"
Your text string will be sent using the bytes in Perl's internal format. In
some cases, Perl will warn you that you're doing something wrong, with a
friendly warning:
.PP
.Vb 1
\&    Wide character in print at example.pl line 2.
.Ve
.PP
Because the internal format is often \s-1UTF\-8\s0, these bugs are hard to spot,
because \s-1UTF\-8\s0 is usually the encoding you wanted! But don't be lazy, and don't
use the fact that Perl's internal format is \s-1UTF\-8\s0 to your advantage. Encode
explicitly to avoid weird bugs, and to show to maintenance programmers that you
thought this through.
.Sh "Is there a way to automatically decode or encode?"
.IX Subsection "Is there a way to automatically decode or encode?"
If all data that comes from a certain handle is encoded in exactly the same
way, you can tell the PerlIO system to automatically decode everything, with
the \f(CW\*(C`encoding\*(C'\fR layer. If you do this, you can't accidentally forget to decode
or encode anymore, on things that use the layered handle.
.PP
You can provide this layer when \f(CW\*(C`open\*(C'\fRing the file:
.PP
.Vb 2
\&    open my $fh, \*(Aq>:encoding(UTF\-8)\*(Aq, $filename;  # auto encoding on write
\&    open my $fh, \*(Aq<:encoding(UTF\-8)\*(Aq, $filename;  # auto decoding on read