perlobj.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.

.\" Automatically generated by Pod::Man 2.16 (Pod::Simple 3.05)
.\"
.\" Standard preamble:
.\" ========================================================================
.de Sh \" Subsection heading
.br
.if t .Sp
.ne 5
.PP
\fB\\$1\fR
.PP
..
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R
.fi
..
.\" Set up some character translations and predefined strings.  \*(-- will
.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
.\" double quote, and \*(R" will give a right double quote.  \*(C+ will
.\" give a nicer C++.  Capital omega is used to do unbreakable dashes and
.\" therefore won't be available.  \*(C` and \*(C' expand to `' in nroff,
.\" nothing in troff, for use with C<>.
.tr \(*W-
.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
.ie n \{\
.    ds -- \(*W-
.    ds PI pi
.    if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
.    if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\"  diablo 12 pitch
.    ds L" ""
.    ds R" ""
.    ds C` ""
.    ds C' ""
'br\}
.el\{\
.    ds -- \|\(em\|
.    ds PI \(*p
.    ds L" ``
.    ds R" ''
'br\}
.\"
.\" Escape single quotes in literal strings from groff's Unicode transform.
.ie \n(.g .ds Aq \(aq
.el       .ds Aq '
.\"
.\" If the F register is turned on, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and index
.\" entries marked with X<> in POD.  Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
.ie \nF \{\
.    de IX
.    tm Index:\\$1\t\\n%\t"\\$2"
..
.    nr % 0
.    rr F
.\}
.el \{\
.    de IX
..
.\}
.\"
.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
.\" Fear.  Run.  Save yourself.  No user-serviceable parts.
.    \" fudge factors for nroff and troff
.if n \{\
.    ds #H 0
.    ds #V .8m
.    ds #F .3m
.    ds #[ \f1
.    ds #] \fP
.\}
.if t \{\
.    ds #H ((1u-(\\\\n(.fu%2u))*.13m)
.    ds #V .6m
.    ds #F 0
.    ds #[ \&
.    ds #] \&
.\}
.    \" simple accents for nroff and troff
.if n \{\
.    ds ' \&
.    ds ` \&
.    ds ^ \&
.    ds , \&
.    ds ~ ~
.    ds /
.\}
.if t \{\
.    ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
.    ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
.    ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u'
.    ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u'
.    ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
.    ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u'
.\}
.    \" troff and (daisy-wheel) nroff accents
.ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V'
.ds 8 \h'\*(#H'\(*b\h'-\*(#H'
.ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#]
.ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H'
.ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u'
.ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#]
.ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#]
.ds ae a\h'-(\w'a'u*4/10)'e
.ds Ae A\h'-(\w'A'u*4/10)'E
.    \" corrections for vroff
.if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u'
.if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u'
.    \" for low resolution devices (crt and lpr)
.if \n(.H>23 .if \n(.V>19 \
\{\
.    ds : e
.    ds 8 ss
.    ds o a
.    ds d- d\h'-1'\(ga
.    ds D- D\h'-1'\(hy
.    ds th \o'bp'
.    ds Th \o'LP'
.    ds ae ae
.    ds Ae AE
.\}
.rm #[ #] #H #V #F C
.\" ========================================================================
.\"
.IX Title "PERLOBJ 1"
.TH PERLOBJ 1 "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.
.if n .ad l
.nh
.SH "NAME"
perlobj \- Perl objects
.IX Xref "object OOP"
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
First you need to understand what references are in Perl.
See perlref for that.  Second, if you still find the following
reference work too complicated, a tutorial on object-oriented programming
in Perl can be found in perltoot and perltooc.
.PP
If you're still with us, then
here are three very simple definitions that you should find reassuring.
.IP "1." 4
An object is simply a reference that happens to know which class it
belongs to.
.IP "2." 4
A class is simply a package that happens to provide methods to deal
with object references.
.IP "3." 4
A method is simply a subroutine that expects an object reference (or
a package name, for class methods) as the first argument.
.PP
We'll cover these points now in more depth.
.Sh "An Object is Simply a Reference"
.IX Xref "object bless constructor new"
.IX Subsection "An Object is Simply a Reference"
Unlike say \*(C+, Perl doesn't provide any special syntax for
constructors.  A constructor is merely a subroutine that returns a
reference to something \*(L"blessed\*(R" into a class, generally the
class that the subroutine is defined in.  Here is a typical
constructor:
.PP
.Vb 2
\&    package Critter;
\&    sub new { bless {} }
.Ve
.PP
That word \f(CW\*(C`new\*(C'\fR isn't special.  You could have written
a construct this way, too:
.PP
.Vb 2
\&    package Critter;
\&    sub spawn { bless {} }
.Ve
.PP
This might even be preferable, because the \*(C+ programmers won't
be tricked into thinking that \f(CW\*(C`new\*(C'\fR works in Perl as it does in \*(C+.
It doesn't.  We recommend that you name your constructors whatever
makes sense in the context of the problem you're solving.  For example,
constructors in the Tk extension to Perl are named after the widgets
they create.
.PP
One thing that's different about Perl constructors compared with those in
\&\*(C+ is that in Perl, they have to allocate their own memory.  (The other
things is that they don't automatically call overridden base-class
constructors.)  The \f(CW\*(C`{}\*(C'\fR allocates an anonymous hash containing no
key/value pairs, and returns it  The \fIbless()\fR takes that reference and
tells the object it references that it's now a Critter, and returns
the reference.  This is for convenience, because the referenced object
itself knows that it has been blessed, and the reference to it could
have been returned directly, like this:
.PP
.Vb 5
\&    sub new {
\&        my $self = {};
\&        bless $self;
\&        return $self;
\&    }
.Ve
.PP
You often see such a thing in more complicated constructors
that wish to call methods in the class as part of the construction:
.PP
.Vb 6
\&    sub new {
\&        my $self = {};
\&        bless $self;
\&        $self\->initialize();
\&        return $self;
\&    }
.Ve
.PP
If you care about inheritance (and you should; see
\&\*(L"Modules: Creation, Use, and Abuse\*(R" in perlmodlib),
then you want to use the two-arg form of bless
so that your constructors may be inherited:
.PP
.Vb 7
\&    sub new {
\&        my $class = shift;
\&        my $self = {};
\&        bless $self, $class;
\&        $self\->initialize();
\&        return $self;
\&    }
.Ve
.PP
Or if you expect people to call not just \f(CW\*(C`CLASS\->new()\*(C'\fR but also
\&\f(CW\*(C`$obj\->new()\*(C'\fR, then use something like the following.  (Note that using
this to call \fInew()\fR on an instance does not automatically perform any
copying.  If you want a shallow or deep copy of an object, you'll have to
specifically allow for that.)  The \fIinitialize()\fR method used will be of
whatever \f(CW$class\fR we blessed the object into:
.PP
.Vb 8
\&    sub new {
\&        my $this = shift;
\&        my $class = ref($this) || $this;
\&        my $self = {};
\&        bless $self, $class;
\&        $self\->initialize();
\&        return $self;
\&    }
.Ve
.PP
Within the class package, the methods will typically deal with the
reference as an ordinary reference.  Outside the class package,
the reference is generally treated as an opaque value that may
be accessed only through the class's methods.
.PP
Although a constructor can in theory re-bless a referenced object
currently belonging to another class, this is almost certainly going
to get you into trouble.  The new class is responsible for all
cleanup later.  The previous blessing is forgotten, as an object
may belong to only one class at a time.  (Although of course it's
free to inherit methods from many classes.)  If you find yourself
having to do this, the parent class is probably misbehaving, though.
.PP
A clarification:  Perl objects are blessed.  References are not.  Objects
know which package they belong to.  References do not.  The \fIbless()\fR
function uses the reference to find the object.  Consider
the following example:
.PP
.Vb 4
\&    $a = {};
\&    $b = $a;
\&    bless $a, BLAH;
\&    print "\e$b is a ", ref($b), "\en";
.Ve
.PP
This reports \f(CW$b\fR as being a \s-1BLAH\s0, so obviously \fIbless()\fR
operated on the object and not on the reference.
.Sh "A Class is Simply a Package"
.IX Xref "class package @ISA inheritance"
.IX Subsection "A Class is Simply a Package"
Unlike say \*(C+, Perl doesn't provide any special syntax for class
definitions.  You use a package as a class by putting method
definitions into the class.
.PP
There is a special array within each package called \f(CW@ISA\fR, which says
where else to look for a method if you can't find it in the current
package.  This is how Perl implements inheritance.  Each element of the
\&\f(CW@ISA\fR array is just the name of another package that happens to be a
class package.  The classes are searched for missing methods in
depth-first, left-to-right order by default (see mro for alternative
search order and other in-depth information).  The classes accessible
through \f(CW@ISA\fR are known as base classes of the current class.
.PP
All classes implicitly inherit from class \f(CW\*(C`UNIVERSAL\*(C'\fR as their
last base class.  Several commonly used methods are automatically
supplied in the \s-1UNIVERSAL\s0 class; see \*(L"Default \s-1UNIVERSAL\s0 methods\*(R" for
more details.
.IX Xref "UNIVERSAL base class class, base"
.PP
If a missing method is found in a base class, it is cached
in the current class for efficiency.  Changing \f(CW@ISA\fR or defining new
subroutines invalidates the cache and causes Perl to do the lookup again.
.PP
If neither the current class, its named base classes, nor the \s-1UNIVERSAL\s0
class contains the requested method, these three places are searched
all over again, this time looking for a method named \s-1\fIAUTOLOAD\s0()\fR.  If an
\&\s-1AUTOLOAD\s0 is found, this method is called on behalf of the missing method,
setting the package global \f(CW$AUTOLOAD\fR to be the fully qualified name of
the method that was intended to be called.
.IX Xref "AUTOLOAD"
.PP
If none of that works, Perl finally gives up and complains.
.PP
If you want to stop the \s-1AUTOLOAD\s0 inheritance say simply
.IX Xref "AUTOLOAD"
.PP
.Vb 1
\&        sub AUTOLOAD;
.Ve
.PP
and the call will die using the name of the sub being called.
.PP
Perl classes do method inheritance only.  Data inheritance is left up
to the class itself.  By and large, this is not a problem in Perl,
because most classes model the attributes of their object using an
anonymous hash, which serves as its own little namespace to be carved up
by the various classes that might want to do something with the object.
The only problem with this is that you can't sure that you aren't using
a piece of the hash that isn't already used.  A reasonable workaround
is to prepend your fieldname in the hash with the package name.
.IX Xref "inheritance, method inheritance, data"
.PP
.Vb 4
\&    sub bump {
\&        my $self = shift;
\&        $self\->{ _\|_PACKAGE_\|_ . ".count"}++;
\&    }
.Ve
.Sh "A Method is Simply a Subroutine"
.IX Xref "method"
.IX Subsection "A Method is Simply a Subroutine"
Unlike say \*(C+, Perl doesn't provide any special syntax for method
definition.  (It does provide a little syntax for method invocation
though.  More on that later.)  A method expects its first argument
to be the object (reference) or package (string) it is being invoked
on.  There are two ways of calling methods, which we'll call class
methods and instance methods.
.PP
A class method expects a class name as the first argument.  It
provides functionality for the class as a whole, not for any
individual object belonging to the class.  Constructors are often
class methods, but see perltoot and perltooc for alternatives.
Many class methods simply ignore their first argument, because they
already know what package they're in and don't care what package
they were invoked via.  (These aren't necessarily the same, because
class methods follow the inheritance tree just like ordinary instance
methods.)  Another typical use for class methods is to look up an
object by name:
.PP
.Vb 4
\&    sub find {
\&        my ($class, $name) = @_;
\&        $objtable{$name};
\&    }
.Ve
.PP
An instance method expects an object reference as its first argument.
Typically it shifts the first argument into a \*(L"self\*(R" or \*(L"this\*(R" variable,
and then uses that as an ordinary reference.
.PP
.Vb 7
\&    sub display {
\&        my $self = shift;
\&        my @keys = @_ ? @_ : sort keys %$self;
\&        foreach $key (@keys) {
\&            print "\et$key => $self\->{$key}\en";
\&        }
\&    }
.Ve