#

    property_writer<PropertyMap, OutputIterator, EventTag>

This is an EventVisitor that can be used to output the property of a vertex or edge at some event-point within an algorithm.

`property_writer` can be used with graph algorithms by wrapping it with the algorithm-specific adaptor, such as `bfs_visitor` and `dfs_visitor`. Also, this event visitor can be combined with other event visitors using `std::pair` to form an EventVisitorList.

### Example

The following is an excerpt from `examples/dave.cpp`.

      std::ostream_iterator cout_int(std::cout, " ");
      std::ostream_iterator cout_char(std::cout, " ");

      boost::breadth_first_search
        (G, vertex(a, G), make_bfs_visitor(
         std::make_pair(write_property(name, cout_char, on_discover_vertex()),
         std::make_pair(write_property(distance.begin(), cout_int,
                                       on_discover_vertex()),
         std::make_pair(print_edge(name, std::cout, on_examine_edge()),
                        print_endl(std::cout, on_finish_vertex()
                        ))))));

### Model of

EventVisitor

### Where Defined

`boost/graph/visitors.hpp`

### Template Parameters

Parameter | Description | Default
--- | --- | ---
`PropertyMap` | A ReadablePropertyMap where the `key_type` is the vertex descriptor type or edge descriptor of the graph (depending on the kind of event tag) and the `value_type` of the property is convertible to the `value_type` of the `OutputIterator`. |
`OutputIterator` | The iterator type used to write out the property values, which must be a model of OutputIterator. |
`EventTag` | The tag to specify when the `property_writer` should be applied during the graph algorithm. |

## Associated Types

Type | Description
--- | ---
`property_writer::event_filter` | This will be the same type as the template parameter `EventTag`.

### Member Functions

Member | Description
--- | ---
`property_writer(PropertyMap pa, OutputIterator out);` | Construct a property writer object with the property map `pa` and output iterator `out`.
`template <class X, class Graph> void operator()(X x, const Graph& g);` | This writes the property value for `x` to the output iterator. `*out++ = get(pa, x);`

### Non-Member Functions

Function | Description
--- | ---
`template <class PropertyMap, class OutputIterator, class Tag> property_writer<PropertyMap, OutputIterator, Tag> write_property(PropertyMap pa, OutputIterator out, Tag);` | A convenient way to create a `property_writer`.

### See Also

Visitor concepts

The following are other event visitors: `distance_recorder`, `predecessor_recorder`, and `time_stamper`.

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