symbol.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 "Symbol 3"
.TH Symbol 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.
.if n .ad l
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.SH "NAME"
Symbol \- manipulate Perl symbols and their names
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    use Symbol;
\&
\&    $sym = gensym;
\&    open($sym, "filename");
\&    $_ = <$sym>;
\&    # etc.
\&
\&    ungensym $sym;      # no effect
\&
\&    # replace *FOO{IO} handle but not $FOO, %FOO, etc.
\&    *FOO = geniosym;
\&
\&    print qualify("x"), "\en";              # "Test::x"
\&    print qualify("x", "FOO"), "\en"        # "FOO::x"
\&    print qualify("BAR::x"), "\en";         # "BAR::x"
\&    print qualify("BAR::x", "FOO"), "\en";  # "BAR::x"
\&    print qualify("STDOUT", "FOO"), "\en";  # "main::STDOUT" (global)
\&    print qualify(\e*x), "\en";              # returns \e*x
\&    print qualify(\e*x, "FOO"), "\en";       # returns \e*x
\&
\&    use strict refs;
\&    print { qualify_to_ref $fh } "foo!\en";
\&    $ref = qualify_to_ref $name, $pkg;
\&
\&    use Symbol qw(delete_package);
\&    delete_package(\*(AqFoo::Bar\*(Aq);
\&    print "deleted\en" unless exists $Foo::{\*(AqBar::\*(Aq};
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`Symbol::gensym\*(C'\fR creates an anonymous glob and returns a reference
to it.  Such a glob reference can be used as a file or directory
handle.
.PP
For backward compatibility with older implementations that didn't
support anonymous globs, \f(CW\*(C`Symbol::ungensym\*(C'\fR is also provided.
But it doesn't do anything.
.PP
\&\f(CW\*(C`Symbol::geniosym\*(C'\fR creates an anonymous \s-1IO\s0 handle.  This can be
assigned into an existing glob without affecting the non-IO portions
of the glob.
.PP
\&\f(CW\*(C`Symbol::qualify\*(C'\fR turns unqualified symbol names into qualified
variable names (e.g. \*(L"myvar\*(R" \-> \*(L"MyPackage::myvar\*(R").  If it is given a
second parameter, \f(CW\*(C`qualify\*(C'\fR uses it as the default package;
otherwise, it uses the package of its caller.  Regardless, global
variable names (e.g. \*(L"\s-1STDOUT\s0\*(R", \*(L"\s-1ENV\s0\*(R", \*(L"\s-1SIG\s0\*(R") are always qualified with
\&\*(L"main::\*(R".
.PP
Qualification applies only to symbol names (strings).  References are
left unchanged under the assumption that they are glob references,
which are qualified by their nature.
.PP
\&\f(CW\*(C`Symbol::qualify_to_ref\*(C'\fR is just like \f(CW\*(C`Symbol::qualify\*(C'\fR except that it
returns a glob ref rather than a symbol name, so you can use the result
even if \f(CW\*(C`use strict \*(Aqrefs\*(Aq\*(C'\fR is in effect.
.PP
\&\f(CW\*(C`Symbol::delete_package\*(C'\fR wipes out a whole package namespace.  Note
this routine is not exported by default\*(--you may want to import it
explicitly.
.SH "BUGS"
.IX Header "BUGS"
\&\f(CW\*(C`Symbol::delete_package\*(C'\fR is a bit too powerful. It undefines every symbol that
lives in the specified package. Since perl, for performance reasons, does not
perform a symbol table lookup each time a function is called or a global
variable is accessed, some code that has already been loaded and that makes use
of symbols in package \f(CW\*(C`Foo\*(C'\fR may stop working after you delete \f(CW\*(C`Foo\*(C'\fR, even if
you reload the \f(CW\*(C`Foo\*(C'\fR module afterwards.