`read_graphviz`

namespace boost {

  template <typename MutableGraph>
  bool read_graphviz(std::istream& in, MutableGraph& graph,
                     dynamic_properties& dp,
                     const std::string& node_id = "node_id");

  template <typename MutableGraph>
  bool read_graphviz(std::string& str, MutableGraph& graph,
                     dynamic_properties& dp,
                     const std::string& node_id = "node_id");

  template <typename InputIterator, typename MutableGraph>
  bool read_graphviz(InputIterator begin, InputIterator end,
                     MutableGraph& graph, dynamic_properties& dp,
                     const std::string& node_id = "node_id");

}

The read_graphviz function interprets a graph described using the GraphViz DOT language and builds a BGL graph that captures that description. Using these functions, you can initialize a graph using data stored as text.

The DOT language can specify both directed and undirected graphs, and read_graphviz differentiates between the two. One must pass read_graphviz an undirected graph when reading an undirected graph; the same is true for directed graphs. Furthermore, read_graphviz will throw an exception if it encounters parallel edges and cannot add them to the graph.

To handle properties expressed in the DOT language, read_graphviz takes a dynamic_properties object and operates on its collection of property maps. The reader passes all the properties encountered to this object, using the GraphViz string keys as the property keys. Furthermore, read_graphviz stores node identifier names under the vertex property map named node_id.

Requirements:

The type of the graph must model the Mutable Graph concept.
The type of the iterator must model the Input Iterator concept.
The property map value types must be default-constructible.

Contents

Where Defined
Exceptions
Example
Building the GraphViz Readers
Notes
See Also
Future Work

Where Defined

<boost/graph/graphviz.hpp>

Exceptions

struct graph_exception : public std::exception {
  virtual ~graph_exception() throw();
  virtual const char* what() const throw() = 0;
};

struct bad_parallel_edge : public graph_exception {
  std::string from;
  std::string to;

  bad_parallel_edge(const std::string&, const std::string&);
  virtual ~bad_parallel_edge() throw();
  const char* what() const throw();
};

struct directed_graph_error : public graph_exception {
  virtual ~directed_graph_error() throw();
  virtual const char* what() const throw();
};

struct undirected_graph_error : public graph_exception {
  virtual ~undirected_graph_error() throw();
  virtual const char* what() const throw();
};

struct bad_graphviz_syntax: public graph_exception {
  std::string errmsg;

  bad_graphviz_syntax(const std::string&);
  virtual ~bad_graphviz_syntax() throw();
  virtual const char* what() const throw();
};

Under certain circumstances, read_graphviz will throw one of the above exceptions. The three concrete exceptions can all be caught using the general graph_exception moniker when greater precision is not needed. In addition, all of the above exceptions derive from the standard std::exception for even more generalized error handling.

The bad_parallel_edge exception is thrown when an attempt to add a parallel edge to the supplied MutableGraph fails. The DOT language supports parallel edges, but some BGL-compatible graph types do not. One example of such a graph is boost::adjacency_list<setS,vecS>, which allows at most one edge can between any two vertices.

The directed_graph_error exception occurs when an undirected graph type is passed to read_graph but the textual representation of the graph is directed, as indicated by the digraph keyword in the DOT language.

The undirected_graph_error exception occurs when a directed graph type is passed to read_graph but the textual representation of the graph is undirected, as indicated by the graph keyword in the DOT language.

The bad_graphviz_syntax exception occurs when the graph input is not a valid GraphViz graph.

Example

The following example illustrates a relatively simple use of the GraphViz reader to populate an adjacency_list graph

// Vertex properties
typedef property < vertex_name_t, std::string,
          property < vertex_color_t, float > > vertex_p;
// Edge properties
typedef property < edge_weight_t, double > edge_p;
// Graph properties
typedef property < graph_name_t, std::string > graph_p;
// adjacency_list-based type
typedef adjacency_list < vecS, vecS, directedS,
  vertex_p, edge_p, graph_p > graph_t;

// Construct an empty graph and prepare the dynamic_property_maps.
graph_t graph(0);
dynamic_properties dp;

property_map<graph_t, vertex_name_t>::type name =
  get(vertex_name, graph);
dp.property("node_id",name);

property_map<graph_t, vertex_color_t>::type mass =
  get(vertex_color, graph);
dp.property("mass",mass);

property_map<graph_t, edge_weight_t>::type weight =
  get(edge_weight, graph);
dp.property("weight",weight);

// Use ref_property_map to turn a graph property into a property map
boost::ref_property_map<graph_t*,std::string>
  gname(get_property(graph,graph_name));
dp.property("name",gname);

// Sample graph as an std::istream;
std::istringstream
  gvgraph("digraph { graph [name=\"graphname\"]  a  c e [mass = 6.66] }");

bool status = read_graphviz(gvgraph,graph,dp,"node_id");

Building the GraphViz Readers

To use the GraphViz readers, you will need to build and link against the "boost_graph" library. This library can be built by following the Boost Jam Build Instructions for the subdirectory libs/graph/build.

Notes

The read_graphviz function does not use any code from the GraphViz distribution to interpret the DOT Language. Rather, the implementation was based on documentation found on the GraphViz web site, as well as experiments run using the dot application. The resulting interpretation may be subtly different from dot for some corner cases that are not well specified.

On successful reading of a graph, every vertex and edge will have an associated value for every respective edge and vertex property encountered while interpreting the graph. These values will be set using the dynamic_properties object. Those edges and vertices that are not explicitly given a value for a property (and that property has no default) will be given the default constructed value of the value type. Be sure that property map value types are default constructible.

read_graphviz treats subgraphs as syntactic sugar. It does not reflect subgraphs as actual entities in the BGL. Rather, they are used to shorten some edge definitions as well as to give a subset of all nodes or edges certain properties. For example, the DOT graphs digraph { a -> subgraph {b -> c} -> e } and digraph { a -> b -> e ; a -> c -> e ; b -> c} are equivalent.

Subgraph IDs refer to subgraphs defined earlier in the graph description. Undefined subgraphs behave as empty subgraphs ({}). This is the same behavior as GraphViz.

Future Work

Passing port information to BGL.

Expanding escape codes in the same way GraphViz does.

Support for optional recognition of subgraphs as distinct entities.