# `write_graphviz`

    (1)
    template < typename VertexListGraph >
    void
    write_graphviz(std::ostream& out, const VertexListGraph& g);

    (2)
    template < typename VertexListGraph, typename VertexPropertyWriter >
    void
    write_graphviz(std::ostream& out, const VertexListGraph& g,
                   VertexPropertyWriter vpw);

    (3)
    template < typename VertexListGraph, typename VertexPropertyWriter,
               typename EdgePropertyWriter >
    void
    write_graphviz(std::ostream& out, const VertexListGraph& g,
                   VertexPropertyWriter vpw, EdgePropertyWriter epw);

    (4)
    template < typename VertexListGraph, typename VertexPropertyWriter,
               typename EdgePropertyWriter, typename GraphPropertyWriter >
    void
    write_graphviz(std::ostream& out, const VertexListGraph& g,
                   VertexPropertyWriter vpw, EdgePropertyWriter epw,
                   GraphPropertyWriter gpw);

This is to write a BGL graph object into a 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 graph into an `std::ostream` where vertex is represented by numerical vertex IDs. 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 gaphviz 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 label. Similarly, the third version and fourth version require edge PropertyWriter, edge PropertyWriter and graph PropertyWriter, respectively.

### `PropertyWriter`

PropertyWriter is used in the `write_graphviz` function to print properties of vertex, edge or graph. 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 is to print a series of "name=value" separated with spaces or a comma or a semicolon in square bracket into an `std::ostream`. The following functor 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
        void operator()(std::ostream& out, const VertexOrEdge& v) const {
          out << "[label=\"" << name[v] << "\"]";
        }
      private:
        Name name;
      };

A PropertyWriter for graph is a functor which is to print a series graph properties into an `std::ostream`. 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;
        }
      };
    }

### Parameters

For version 1:

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.

For version 2:

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.

IN: `VertexPropertyWriter vpw`

> A functor that models PropertyWriter concept to print properties of a vertex.

For version 3:

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.

IN: `VertexPropertyWriter vpw`

> A functor that models PropertyWriter concept to print properties of a vertex.

IN: `EdgePropertyWriter epw`

> A functor that models PropertyWriter concept to print properties of an edge.

For version 4:

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.

IN: `VertexPropertyWriter vpw`

> A functor that models PropertyWriter concept to print properties of a vertex.

IN: `EdgePropertyWriter epw`

> A functor that models PropertyWriter concept to print properties of an edge.

IN: `GeaphPropertyWriter epw`

> A functor that models PropertyWriter concept to print properties of a graph.

### Example

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

    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 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];
      fill(weights, weights + nedges, 1);

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

      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"];
    edge[style="dotted"];
    6 -> 0;
    }

### 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)