# `write_graphml`

    template<typename Graph>
    void
    write_graphml(std::ostream& out, const Graph& g, const dynamic_properties& dp,
                  bool ordered_vertices=false);

    template<typename Graph, typename VertexIndexMap>
    void
    write_graphml(std::ostream& out, const Graph& g, VertexIndexMap vertex_index,
                  const dynamic_properties& dp, bool ordered_vertices=false);

This is to write a BGL graph object into an output stream in the graphml format. Both overloads of `write_graphml` 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_graphml. The second overload must be used when the graph doesn't have an internal vertex index map, which must then be supplied with the appropriate parameter.

Contents

- Where Defined
- Parameters
- Example
- See Also
- Notes

# Where Defined

`<boost/graph/graphml.hpp>`

# 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. If the graph doesn't have an internal `vertex_index` property map, one must be supplied with the vertex_index parameter.
IN: `VertexIndexMap vertex_index`
  A vertex property map containing the indexes in the range [0,num_vertices(g)].
IN: `dynamic_properties& dp`
  Contains all of the vertex and edge properties that should be emitted by the graphml writer.
IN: `bool ordered_vertices`
  This tells whether or not the order of the vertices from vertices(g) matches the order of the indexes. If `true`, the `parse.nodeids` graph attribute will be set to `canonical`. Otherwise it will be set to `free`.

# Example

This example demonstrates using BGL-graphml interface to write a BGL graph into a graphml 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<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);

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

        graph_traits<Graph>::vertex_iterator v, v_end;
        for (tie(v,v_end) = vertices(g); v != v_end; ++v)
            put(vertex_color_t(), g, *v, name[*v]);

        graph_traits<Graph>::edge_iterator e, e_end;
        for (tie(e,e_end) = edges(g); e != e_end; ++e)
            put(edge_weight_t(), g, *e, 3);

        dynamic_properties dp;
        dp.property("name", get(vertex_color_t(), g));
        dp.property("weight", get(edge_weight_t(), g));

        write_graphml(std::cout, g, dp, true);
     }

The output will be:

    <?xml version="1.0" encoding="UTF-8"?>
    <graphml xmlns="http://graphml.graphdrawing.org/xmlns/graphml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://graphml.graphdrawing.org/xmlns/graphml http://graphml.graphdrawing.org/xmlns/graphml/graphml-attributes-1.0rc.xsd">
      <key id="key0" for="node" attr.name="name" attr.type="string" />
      <key id="key1" for="edge" attr.name="weight" attr.type="int" />
      <graph id="G" edgedefault="directed" parse.nodeids="canonical" parse.edgeids="canonical" parse.order="nodesfirst">
        <node id="n0">
          <data key="key0">dax.h</data>
        </node>
        <node id="n1">
          <data key="key0">yow.h</data>
        </node>
        <node id="n2">
          <data key="key0">boz.h</data>
        </node>
        <node id="n3">
          <data key="key0">zow.h</data>
        </node>
        <node id="n4">
          <data key="key0">foo.cpp</data>
        </node>
        <node id="n5">
          <data key="key0">foo.o</data>
        </node>
        <node id="n6">
          <data key="key0">bar.cpp</data>
        </node>
        <node id="n7">
          <data key="key0">bar.o</data>
        </node>
        <node id="n8">
          <data key="key0">libfoobar.a</data>
        </node>
        <node id="n9">
          <data key="key0">zig.cpp</data>
        </node>
        <node id="n10">
          <data key="key0">zig.o</data>
        </node>
        <node id="n11">
          <data key="key0">zag.cpp</data>
        </node>
        <node id="n12">
          <data key="key0">zag.o</data>
        </node>
        <node id="n13">
          <data key="key0">libzigzag.a</data>
        </node>
        <node id="n14">
          <data key="key0">killerapp</data>
        </node>
        <edge id="e0" source="n0" target="n4">
          <data key="key1">3</data>
        </edge>
        <edge id="e1" source="n0" target="n6">
          <data key="key1">3</data>
        </edge>
        <edge id="e2" source="n0" target="n1">
          <data key="key1">3</data>
        </edge>
        <edge id="e3" source="n1" target="n6">
          <data key="key1">3</data>
        </edge>
        <edge id="e4" source="n1" target="n11">
          <data key="key1">3</data>
        </edge>
        <edge id="e5" source="n2" target="n6">
          <data key="key1">3</data>
        </edge>
        <edge id="e6" source="n2" target="n9">
           <data key="key1">3</data>
        </edge>
        <edge id="e7" source="n2" target="n11">
          <data key="key1">3</data>
        </edge>
        <edge id="e8" source="n3" target="n4">
          <data key="key1">3</data>
        </edge>
        <edge id="e9" source="n4" target="n5">
          <data key="key1">3</data>
        </edge>
        <edge id="e10" source="n5" target="n8">
          <data key="key1">3</data>
        </edge>
        <edge id="e11" source="n6" target="n7">
          <data key="key1">3</data>
        </edge>
        <edge id="e12" source="n7" target="n8">
          <data key="key1">3</data>
        </edge>
        <edge id="e13" source="n8" target="n13">
          <data key="key1">3</data>
        </edge>
        <edge id="e14" source="n9" target="n10">
          <data key="key1">3</data>
        </edge>
        <edge id="e15" source="n10" target="n13">
          <data key="key1">3</data>
        </edge>
        <edge id="e16" source="n11" target="n12">
          <data key="key1">3</data>
        </edge>
        <edge id="e17" source="n12" target="n13">
          <data key="key1">3</data>
        </edge>
        <edge id="e18" source="n13" target="n14">
          <data key="key1">3</data>
        </edge>
      </graph>
    </graphml>

# See Also

_read_graphml

# Notes

> - Note that you can use graphml file write facilities without linking against the `boost_graph` library.