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Man Pages

Manual Reference Pages  -  GRAPH::WRITER (3)

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Graph::Writer - base class for Graph file format writers



  package Graph::Writer::MyFormat;
  use Graph::Writer;
  use vars qw(@ISA);
  @ISA = qw(Graph::Writer);

  sub _write_graph
    my ($self, $graph, $FILE) = @_;

    # write $graph to $FILE


<B>Graph::WriterB> is a base class for Graph file format writers. A particular subclass of Graph::Writer will handle a specific file format, and generate a Graph, represented using Jarkko Hietaniemi’s Graph class.

You should never create an instance of this class yourself, it is only meant for subclassing. If you try to create an instance of Graph::Writer, the constructor will throw an exception.



Constructor - generate a new writer instance. This is a virtual method, or whatever the correct lingo is. You’re not meant to call this on the base class, it is inherited by the subclasses. Ie if you do something like:

  $writer = Graph::Writer->new();

It will throw an exception.


Read a graph from the specified file:

  $graph = $writer->write_graph($file);

The $file argument can either be a filename, or a filehandle for a previously opened file.


To create your own graph format writer, create a module which subclasses <B>Graph::WriterB>. For example, suppose DGF is a directed graph format - create a <B>Graph::Writer::DGFB> module, with the following structure:

  package Graph::Writer::DGF;

  use Graph::Writer;
  use vars qw(@ISA);
  @ISA = qw(Graph::Writer);

  sub _write_graph
    my $self  = shift;
    my $graph = shift;
    my $FILE  = shift;

    while (<$FILE>)

    return 1;


Note the leading underscore on the <B>B>_write_graph()<B>B> method. The base class provides the public method, and invokes the private method which you’re expected to provide, as above.

If you want to perform additional initialisation at construction time, you can provide an <B>B>_init()<B>B> method, which will be invoked by the base class’s constructor. You should invoke the superclass’s initialiser as well, as follows:

  sub _init
    my $self = shift;


    # your initialisation here

Someone can then use your class as follows:

  use Graph::Writer::DGF;

  $writer = Graph::Writer::DGF->new();
  $writer->write_graph($graph, foo.dgf);


Graph Jarkko Hietaniemi’s modules for representing directed graphs, available from CPAN under modules/by-module/Graph/
Algorithms in Perl The O’Reilly book has a chapter on directed graphs, which is based around Jarkko’s modules.
Graph::Writer::Dot A simple subclass of this class for writing graphs in the file format used by dot, which is part of the graphviz package from AT&T.
Graph::Writer::VCG A simple subclass of this class for writing graphs in the file format used by VCG, a tool for visualising directed graphs, initially developed for visualising compiler graphs.
Graph::Writer::XML A simple subclass of this class for writing graphs as XML, using a simple graph markup.
Graph::Reader A baseclass for Graph file format readers.




Neil Bowers <>


Copyright (c) 2001-2012, Neil Bowers. All rights reserved. Copyright (c) 2001, Canon Research Centre Europe. All rights reserved.

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

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perl v5.20.3 GRAPH::WRITER (3) 2015-10-30

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