perllexwarn.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.

The current hierarchy is:
.PP
.Vb 10
\&  all \-+
\&       |
\&       +\- closure
\&       |
\&       +\- deprecated
\&       |
\&       +\- exiting
\&       |
\&       +\- glob
\&       |
\&       +\- io \-\-\-\-\-\-\-\-\-\-\-+
\&       |                |
\&       |                +\- closed
\&       |                |
\&       |                +\- exec
\&       |                |
\&       |                +\- layer
\&       |                |
\&       |                +\- newline
\&       |                |
\&       |                +\- pipe
\&       |                |
\&       |                +\- unopened
\&       |
\&       +\- misc
\&       |
\&       +\- numeric
\&       |
\&       +\- once
\&       |
\&       +\- overflow
\&       |
\&       +\- pack
\&       |
\&       +\- portable
\&       |
\&       +\- recursion
\&       |
\&       +\- redefine
\&       |
\&       +\- regexp
\&       |
\&       +\- severe \-\-\-\-\-\-\-+
\&       |                |
\&       |                +\- debugging
\&       |                |
\&       |                +\- inplace
\&       |                |
\&       |                +\- internal
\&       |                |
\&       |                +\- malloc
\&       |
\&       +\- signal
\&       |
\&       +\- substr
\&       |
\&       +\- syntax \-\-\-\-\-\-\-+
\&       |                |
\&       |                +\- ambiguous
\&       |                |
\&       |                +\- bareword
\&       |                |
\&       |                +\- digit
\&       |                |
\&       |                +\- parenthesis
\&       |                |
\&       |                +\- precedence
\&       |                |
\&       |                +\- printf
\&       |                |
\&       |                +\- prototype
\&       |                |
\&       |                +\- qw
\&       |                |
\&       |                +\- reserved
\&       |                |
\&       |                +\- semicolon
\&       |
\&       +\- taint
\&       |
\&       +\- threads
\&       |
\&       +\- uninitialized
\&       |
\&       +\- unpack
\&       |
\&       +\- untie
\&       |
\&       +\- utf8
\&       |
\&       +\- void
.Ve
.PP
Just like the \*(L"strict\*(R" pragma any of these categories can be combined
.PP
.Vb 2
\&    use warnings qw(void redefine);
\&    no warnings qw(io syntax untie);
.Ve
.PP
Also like the \*(L"strict\*(R" pragma, if there is more than one instance of the
\&\f(CW\*(C`warnings\*(C'\fR pragma in a given scope the cumulative effect is additive.
.PP
.Vb 5
\&    use warnings qw(void); # only "void" warnings enabled
\&    ...
\&    use warnings qw(io);   # only "void" & "io" warnings enabled
\&    ...
\&    no warnings qw(void);  # only "io" warnings enabled
.Ve
.PP
To determine which category a specific warning has been assigned to see
perldiag.
.PP
Note: In Perl 5.6.1, the lexical warnings category \*(L"deprecated\*(R" was a
sub-category of the \*(L"syntax\*(R" category. It is now a top-level category
in its own right.
.Sh "Fatal Warnings"
.IX Xref "warning, fatal"
.IX Subsection "Fatal Warnings"
The presence of the word \*(L"\s-1FATAL\s0\*(R" in the category list will escalate any
warnings detected from the categories specified in the lexical scope
into fatal errors. In the code below, the use of \f(CW\*(C`time\*(C'\fR, \f(CW\*(C`length\*(C'\fR
and \f(CW\*(C`join\*(C'\fR can all produce a \f(CW"Useless use of xxx in void context"\fR
warning.
.PP
.Vb 1
\&    use warnings;
\&
\&    time;
\&
\&    {
\&        use warnings FATAL => qw(void);
\&        length "abc";
\&    }
\&
\&    join "", 1,2,3;
\&
\&    print "done\en";
.Ve
.PP
When run it produces this output
.PP
.Vb 2
\&    Useless use of time in void context at fatal line 3.
\&    Useless use of length in void context at fatal line 7.
.Ve
.PP
The scope where \f(CW\*(C`length\*(C'\fR is used has escalated the \f(CW\*(C`void\*(C'\fR warnings
category into a fatal error, so the program terminates immediately it
encounters the warning.
.PP
To explicitly turn off a \*(L"\s-1FATAL\s0\*(R" warning you just disable the warning
it is associated with.  So, for example, to disable the \*(L"void\*(R" warning
in the example above, either of these will do the trick:
.PP
.Vb 2
\&    no warnings qw(void);
\&    no warnings FATAL => qw(void);
.Ve
.PP
If you want to downgrade a warning that has been escalated into a fatal
error back to a normal warning, you can use the \*(L"\s-1NONFATAL\s0\*(R" keyword. For
example, the code below will promote all warnings into fatal errors,
except for those in the \*(L"syntax\*(R" category.
.PP
.Vb 1
\&    use warnings FATAL => \*(Aqall\*(Aq, NONFATAL => \*(Aqsyntax\*(Aq;
.Ve
.Sh "Reporting Warnings from a Module"
.IX Xref "warning, reporting warning, registering"
.IX Subsection "Reporting Warnings from a Module"
The \f(CW\*(C`warnings\*(C'\fR pragma provides a number of functions that are useful for
module authors. These are used when you want to report a module-specific
warning to a calling module has enabled warnings via the \f(CW\*(C`warnings\*(C'\fR
pragma.
.PP
Consider the module \f(CW\*(C`MyMod::Abc\*(C'\fR below.
.PP
.Vb 1
\&    package MyMod::Abc;
\&
\&    use warnings::register;
\&
\&    sub open {
\&        my $path = shift;
\&        if ($path !~ m#^/#) {
\&            warnings::warn("changing relative path to /var/abc")
\&                if warnings::enabled();
\&            $path = "/var/abc/$path";
\&        }
\&    }
\&
\&    1;
.Ve
.PP
The call to \f(CW\*(C`warnings::register\*(C'\fR will create a new warnings category
called \*(L"MyMod::abc\*(R", i.e. the new category name matches the current
package name. The \f(CW\*(C`open\*(C'\fR function in the module will display a warning
message if it gets given a relative path as a parameter. This warnings
will only be displayed if the code that uses \f(CW\*(C`MyMod::Abc\*(C'\fR has actually
enabled them with the \f(CW\*(C`warnings\*(C'\fR pragma like below.
.PP
.Vb 4
\&    use MyMod::Abc;
\&    use warnings \*(AqMyMod::Abc\*(Aq;
\&    ...
\&    abc::open("../fred.txt");
.Ve
.PP
It is also possible to test whether the pre-defined warnings categories are
set in the calling module with the \f(CW\*(C`warnings::enabled\*(C'\fR function. Consider
this snippet of code:
.PP
.Vb 1
\&    package MyMod::Abc;
\&
\&    sub open {
\&        warnings::warnif("deprecated", 
\&                         "open is deprecated, use new instead");
\&        new(@_);
\&    }
\&
\&    sub new
\&    ...
\&    1;
.Ve
.PP
The function \f(CW\*(C`open\*(C'\fR has been deprecated, so code has been included to
display a warning message whenever the calling module has (at least) the
\&\*(L"deprecated\*(R" warnings category enabled. Something like this, say.
.PP
.Vb 4
\&    use warnings \*(Aqdeprecated\*(Aq;
\&    use MyMod::Abc;
\&    ...
\&    MyMod::Abc::open($filename);
.Ve
.PP
Either the \f(CW\*(C`warnings::warn\*(C'\fR or \f(CW\*(C`warnings::warnif\*(C'\fR function should be
used to actually display the warnings message. This is because they can
make use of the feature that allows warnings to be escalated into fatal
errors. So in this case
.PP
.Vb 4
\&    use MyMod::Abc;
\&    use warnings FATAL => \*(AqMyMod::Abc\*(Aq;
\&    ...
\&    MyMod::Abc::open(\*(Aq../fred.txt\*(Aq);
.Ve
.PP
the \f(CW\*(C`warnings::warnif\*(C'\fR function will detect this and die after
displaying the warning message.
.PP
The three warnings functions, \f(CW\*(C`warnings::warn\*(C'\fR, \f(CW\*(C`warnings::warnif\*(C'\fR
and \f(CW\*(C`warnings::enabled\*(C'\fR can optionally take an object reference in place
of a category name. In this case the functions will use the class name
of the object as the warnings category.
.PP
Consider this example:
.PP
.Vb 1
\&    package Original;
\&
\&    no warnings;
\&    use warnings::register;
\&
\&    sub new
\&    {
\&        my $class = shift;
\&        bless [], $class;
\&    }
\&
\&    sub check
\&    {
\&        my $self = shift;
\&        my $value = shift;
\&
\&        if ($value % 2 && warnings::enabled($self))
\&          { warnings::warn($self, "Odd numbers are unsafe") }
\&    }
\&
\&    sub doit
\&    {
\&        my $self = shift;
\&        my $value = shift;
\&        $self\->check($value);
\&        # ...
\&    }
\&
\&    1;
\&
\&    package Derived;
\&
\&    use warnings::register;
\&    use Original;
\&    our @ISA = qw( Original );
\&    sub new
\&    {
\&        my $class = shift;
\&        bless [], $class;
\&    }
\&
\&
\&    1;
.Ve
.PP
The code below makes use of both modules, but it only enables warnings from 
\&\f(CW\*(C`Derived\*(C'\fR.
.PP
.Vb 7
\&    use Original;
\&    use Derived;
\&    use warnings \*(AqDerived\*(Aq;
\&    my $a = Original\->new();
\&    $a\->doit(1);
\&    my $b = Derived\->new();
\&    $a\->doit(1);
.Ve
.PP
When this code is run only the \f(CW\*(C`Derived\*(C'\fR object, \f(CW$b\fR, will generate
a warning.
.PP
.Vb 1
\&    Odd numbers are unsafe at main.pl line 7
.Ve
.PP
Notice also that the warning is reported at the line where the object is first
used.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
warnings, perldiag.
.SH "AUTHOR"
.IX Header "AUTHOR"
Paul Marquess