# `write_graphviz`

    // Output graph structure without properties.
    template < typename VertexListGraph >
    void
    write_graphviz(std::ostream& out, const VertexListGraph& g);

    // Graph structure with customized property output
    template < typename VertexListGraph, typename VertexPropertyWriter >
    void
    write_graphviz(std::ostream& out, const VertexListGraph& g,
                   VertexPropertyWriter vpw);

    template < typename VertexListGraph, typename VertexPropertyWriter,
               typename EdgePropertyWriter >
    void
    write_graphviz(std::ostream& out, const VertexListGraph& g,
                   VertexPropertyWriter vpw, EdgePropertyWriter epw);

    template < typename VertexListGraph, typename VertexPropertyWriter,
               typename EdgePropertyWriter, typename GraphPropertyWriter >
    void
    write_graphviz(std::ostream& out, const VertexListGraph& g,
                   VertexPropertyWriter vpw, EdgePropertyWriter epw,
                   GraphPropertyWriter gpw);

    template < typename VertexListGraph, typename VertexPropertyWriter,
               typename EdgePropertyWriter, typename GraphPropertyWriter,
               typename VertexID >
    void
    write_graphviz(std::ostream& out, const VertexListGraph& g,
                   VertexPropertyWriter vpw, EdgePropertyWriter epw,
                   GraphPropertyWriter gpw, VertexID vertex_id);

    // Graph structure with dynamic property output
    template<typename Graph>
    void
    write_graphviz(std::ostream& out, const Graph& g,
                   const dynamic_properties& dp,
                   const std::string& node_id = "node_id");

    template<typename Graph, typename VertexID>
    void
    write_graphviz(std::ostream& out, const Graph& g,
                   const dynamic_properties& dp, const std::string& node_id,
                   VertexID vertex_id);

This is to write a BGL graph object into an output stream in graphviz dot format so that users can make use of AT&T graphviz to draw a picture with nice layout.

The first version with two parameters will write the graph into a `std::ostream` where each vertex is represented by its numerical vertex ID. If users have either interior or exterior properties for each vertex in the graph, the second version above provides a way to print those properties into the graphviz format file. For example, if each vertex in the graph has its label through property map object `name`, users can use the second version:

      write_graph(out, g, make_label_writer(name));

The utility function `make_label_writer` returns a predefined PropertyWriter for vertex labels. Similarly, the third version and fourth version require vertex PropertyWriter, edge PropertyWriter, and graph PropertyWriter, respectively.

The final two overloads of `write_graphviz` will emit all of the properties stored in the `dynamic_properties` object, thereby retaining the properties that have been read in through the dual function `read_graphviz`. With these overloads, `node_id` is the name of the property map that stores the IDs of each node for use in the output (if it is stored in the `dynamic_properties` structure); alternatively, one may provide an arbitrary property map for `vertex_id` giving the vertex identifiers. In this case, the name of `node_id` must still be supplied to suppress its output as a label of the vertices.

### Where Defined

`boost/graph/graphviz.hpp`

### `PropertyWriter`

PropertyWriter is used in the `write_graphviz` function to print vertex, edge or graph properties. There are two types of PropertyWriter. One is for a vertex or edge. The other is for a graph. Thus, users could easily extend the `write_graphviz` function by creating their own PropertyWriter only.

A PropertyWriter for vertices or edges is a functor which can be called with two parameters: `std::ostream` and either a vertex or an edge descriptor. It should output a pair of brackets with a series of assigments "name=value" inside. Each assignment should be separated either with space, with comma, or with semicolon. The following functor, provided by BGL, is the example of PropertyWriter for vertices or edges. It is used to print the label of each vertex or edge.

      template <class Name>
      class label_writer {
      public:
        label_writer(Name _name) : name(_name) {}
        template <class VertexOrEdge>
        void operator()(std::ostream& out, const VertexOrEdge& v) const {
          out << "[label=\"" << name[v] << "\"]";
        }
      private:
        Name name;
      };

A function to conveniently create this writer is provided:

    template < class Name >
    label_writer<Name>
    make_label_writer(Name n);

A PropertyWriter for graphs is a functor which is called with one parameter of type `std::ostream` and should print a series of graph properties. The following code excerpt is an example of a PropertyWriter for a graph.

      struct sample_graph_writer {
        void operator()(std::ostream& out) const {
          out << "graph [bgcolor=lightgrey]" << std::endl;
          out << "node [shape=circle color=white]" << std::endl;
          out << "edge [style=dashed]" << std::endl;
        }
      };
    }

There exists a class `default_writer`, which can be used as both vertex/edge and graph property writer, and does nothing. It comes handy when only edge properties must be written, but function interface requries to pass vertex property writer as well.

### Parameters

OUT: `std::ostream& out`

> A standard `std::ostream` object.

IN: `VertexListGraph& g`

> A directed or undirected graph. The graph's type must be a model of VertexListGraph. Also the graph must have an internal `vertex_index` property map.

IN: `VertexPropertyWriter vpw`

> A functor that models PropertyWriter concept to print properties of a vertex.
> Default: `default_writer()`

IN: `EdgePropertyWriter epw`

> A functor that models PropertyWriter concept to print properties of an edge.
> Default: `default_writer()`

IN: `GraphPropertyWriter epw`

> A functor that models PropertyWriter concept to print properties of a graph.
> Default: `default_writer()`

IN: `dynamic_properties& dp`

> Contains all of the vertex and edge properties that should be emitted by the GraphViz writer.

IN: `const std::string& node_id`

> The name of the property map that provides identifiers for the vertices in the graph.
> Default: `"node_id"`

IN: `VertexID vertex_id`

> A property map that models Readable Property Map whose key type is the vertex descriptor of the graph and whose value type can be written to a stream. The value should be a unique descriptor that can be used to name a node in a Graphviz file (so it should not, for instance, have any spaces in it).
> Default: If no `dynamic_properties` object is provided, `get(vertex_index, g)`. Otherwise, a dynamic property map that accesses the property map named `node_id`.

### Example

This example demonstrates using BGL-graphviz interface to write a BGL graph into a graphviz format file.

    #include <boost/graph/graphviz.hpp>

    enum files_e { dax_h, yow_h, boz_h, zow_h, foo_cpp,
                   foo_o, bar_cpp, bar_o, libfoobar_a,
                   zig_cpp, zig_o, zag_cpp, zag_o,
                     libzigzag_a, killerapp, N };
    const char* name[] = { "dax.h", "yow.h", "boz.h", "zow.h", "foo.cpp",
                           "foo.o", "bar.cpp", "bar.o", "libfoobar.a",
                           "zig.cpp", "zig.o", "zag.cpp", "zag.o",
                           "libzigzag.a", "killerapp" };

    int main(int,char*[])
    {

      typedef pair<int,int> Edge;
      Edge used_by[] = {
        Edge(dax_h, foo_cpp), Edge(dax_h, bar_cpp), Edge(dax_h, yow_h),
        Edge(yow_h, bar_cpp), Edge(yow_h, zag_cpp),
        Edge(boz_h, bar_cpp), Edge(boz_h, zig_cpp), Edge(boz_h, zag_cpp),
        Edge(zow_h, foo_cpp),
        Edge(foo_cpp, foo_o),
        Edge(foo_o, libfoobar_a),
        Edge(bar_cpp, bar_o),
        Edge(bar_o, libfoobar_a),
        Edge(libfoobar_a, libzigzag_a),
        Edge(zig_cpp, zig_o),
        Edge(zig_o, libzigzag_a),
        Edge(zag_cpp, zag_o),
        Edge(zag_o, libzigzag_a),
        Edge(libzigzag_a, killerapp)
      };
      const int nedges = sizeof(used_by)/sizeof(Edge);
      int weights[nedges];
      std::fill(weights, weights + nedges, 1);

      using namespace boost;

      typedef adjacency_list< vecS, vecS, directedS,
          property< vertex_color_t, default_color_type >,
          property< edge_weight_t, int >
        > Graph;
      Graph g(used_by, used_by + nedges, weights, N);

      write_graphviz(std::cout, g, make_label_writer(name));
    }

The output will be:

    digraph G {
    0 -> 4;
    0 -> 6;
    0 -> 1;
    0 [label="dax.h"];
    1 -> 6;
    1 -> 11;
    1 [label="yow.h"];
    2 -> 6;
    2 -> 9;
    2 -> 11;
    2 [label="boz.h"];
    3 -> 4;
    3 [label="zow.h"];
    4 -> 5;
    4 [label="foo.cpp"];
    5 -> 8;
    5 [label="foo.o"];
    6 -> 7;
    6 [label="bar.cpp"];
    7 -> 8;
    7 [label="bar.o"];
    8 -> 13;
    8 [label="libfoobar.a"];
    9 -> 10;
    9 [label="zig.cpp"];
    10 -> 13;
    10 [label="zig.o"];
    11 -> 12;
    11 [label="zag.cpp"];
    12 -> 13;
    12 [label="zag.o"];
    13 -> 14;
    13 [label="libzigzag.a"];
    14;
    14 [label="killerapp"];
    6 -> 0;
    }

The examples directory contains an example using `dynamic_properties`.

### See Also

`read_graphviz`

### Notes

Note that you can use Graphviz dot file write facilities without the library `libbglviz.a`.

Copyright © 2000-2001 | Lie-Quan Lee, Indiana University (llee@cs.indiana.edu) Jeremy Siek, Indiana University (jsiek@osl.iu.edu)