Graph::Error(3)

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Graph::Error(3)User Contributed Perl


NAME

       GD::Graph::Error - Error handling for GD::Graph classes

SYNOPSIS

       use GD::Graph::Error_subclass;

DESCRIPTION

       This class is a parent for all GD::Graph classes, includ-
       ing GD::Graph::Data, and offers error and warning handling
       and some debugging control.

       Errors are stored in a lexical hash in this package, so
       the implementation of the subclass should be irrelevant.

PUBLIC METHODS

       These methods can be used by users of any of the sub-
       classes of GD::Graph::Error to get at the errors of
       objects or classes.

       $object->error() OR Class->error()

       Returns a list of all the errors that the current object
       has accumulated. In scalar context, returns the last
       error. If called as a class method it works at a class
       level. This is handy when a constructor fails, for exam-
       ple:

         my $data = GD::Graph::Data->new()
             or die GD::Graph::Data->error;
         $data->read(file => '/foo/bar.data')
             or die $data->error;

       or if you really are only interested in the last error:

         $data->read(file => '/foo/bar.data')
             or die scalar $data->error;

       This implementation does not clear the error list, so if
       you don't die on errors, you will need to make sure to
       never ask for anything but the last error (put this in
       scalar context) or to call "clear_error()" now and again.

       Errors are more verbose about where the errors originated
       if the $GD::Graph::Error::Debug variable is set to a true
       value, and even more verbose if this value is larger than
       5.

       If $Debug is larger than 3, both of these will always
       return the full list of errors and warnings (although the
       meaning of "has_warning" and "has_error" does not change).

       $object->has_error() OR Class->has_error()


       $object->has_warning() OR Class->has_warning()

       Returns true if there are pending errors (warnings) for
       the object (or class). To be more precise, it returns a
       list of errors in list context, and the number of errors
       in scalar context.

       This allows you to check for errors and warnings after a
       large number of operations which each might fail:

         $data->read(file => '/foo/bar.data') or die $data->error;
         while (my @foo = $sth->fetchrow_array)
         {
             $data->add_point(@foo);
         }
         $data->set_x(12, 'Foo');
         $data->has_warning and warn $data->warning;
         $data->has_error   and die  $data->error;

       The reason to call this, instead of just calling "error()"
       or "warning()" and looking at its return value, is that
       this method is much more efficient and fast.

       If you want to count anything as bad, just set $ErrorLevel
       to 0, after which you only need to call "has_error".

       $object->clear_errors() or Class->clear_errors()

       Clears all outstanding errors.

PROTECTED METHODS

       These methods are only to be called from within this class
       and its Subclasses.

       $object->_set_error(arg) or Class->_set_error(arg)


       $object->_set_warning(arg) or Class->_set_warning(arg)

       Subclasses call this to set an error. The argument can be
       a reference to an array, of which the first element should
       be the error level, and the second element the error mes-
       sage. Alternatively, it can just be the message, in which
       case the error level will be assumed to be $ErrorLevel.

       If the error level is >= $CriticalLevel the program will
       die, using Carp::croak to display the current message, as
       well as all the other error messages pending.

       In the current implementation these are almost identical
       when called with a scalar argument, except that the
       default ewrror level is different. When called with an
       array reference, they are identical in function. This may
       change in the future. They're mainly here for code clar-
       ity.

       $object->_move_errors

       Move errors from an object into the class it belongs to.
       This can be useful if something nasty happens in the con-
       structor, while instantiating one of these objects, and
       you need to move these errors into the class space before
       returning. (see GD::Graph::Data::new for an example)

VARIABLES

       $GD::Graph::Error::Debug

       The higher this value, the more verbose error messages
       will be. At the moment, any true value will cause the line
       number and source file of the caller at the top of the
       stack to be included, a value of more than 2 will include
       the error severity, and a value of more than 5 will also
       include the direct caller's (i.e. the spot where the error
       message was generated) line number and package. Default:
       0.

       $GD::Graph::Error::ErrorLevel

       Errors levels below this value will be counted as warn-
       ings, and error levels above (and inclusive) up to $Criti-
       calLevel will be counted as errors. This is also the
       default error level for the "_set_error()" method. This
       value should be 0 or larger, and smaller than $Critical-
       Level. Default: 5.

       $GD::Graph::Error::CriticalLevel

       Any errorlevel of or above this level will immediately
       cause the program to die with the specified message, using
       Carp::croak. Default: 10.

NOTES

       As with all Modules for Perl: Please stick to using the
       interface. If you try to fiddle too much with knowledge of
       the internals of this module, you could get burned. I may
       change them at any time.

AUTHOR

       Martien Verbruggen <mgjv@tradingpost.com.au>

       Copyright

       (c) Martien Verbruggen.

       All rights reserved. This package is free software; you
       can redistribute it and/or modify it under the same terms
       as Perl itself.

SEE ALSO

       GD::Graph, GD::Graph::Data



perl v5.8.0                 2003-02-10            Graph::Error(3)

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