property_writer

Writes the property value of a vertex or edge to an output iterator when an event occurs. Useful for debugging or logging during a graph traversal.

Defined in: <boost/graph/visitors.hpp>
Models: EventVisitor
Typical event: any (vertex or edge), e.g. on_discover_vertex, on_examine_edge

To use it, wrap it in an algorithm adaptor and optionally combine it with other event visitors; see the visitors overview.

Synopsis

template <typename PropertyMap, typename OutputIterator, typename EventTag>
struct property_writer {
  typedef EventTag event_filter;
  property_writer(PropertyMap pa, OutputIterator out);

  template <class T, class Graph>
  void operator()(T x, Graph& g);
};

template <typename PropertyMap, typename OutputIterator, typename EventTag>
property_writer<PropertyMap, OutputIterator, EventTag>
write_property(PropertyMap pa, OutputIterator out, EventTag);

Template Parameters

Parameter Description

Parameter	Description
`PropertyMap`	A ReadablePropertyMap whose key type is the graph’s vertex or edge descriptor (depending on the event tag), and whose value type is writable to the output iterator.
`OutputIterator`	The output iterator the property values are written to.
`EventTag`	The event at which to write. May be any event, vertex or edge.

PropertyMap

A ReadablePropertyMap whose key type is the graph’s vertex or edge descriptor (depending on the event tag), and whose value type is writable to the output iterator.

OutputIterator

The output iterator the property values are written to.

EventTag

The event at which to write. May be any event, vertex or edge.

Associated Types

Type Description

Type	Description
`event_filter`	The event tag the visitor responds to. Same type as `EventTag`.

event_filter

The event tag the visitor responds to. Same type as EventTag.

Member Functions

Member Description

Member	Description
`property_writer(PropertyMap pa, OutputIterator out)`	Constructs a writer reading from the property map `pa` and writing to `out`.
`void operator()(T x, Graph& g)`	Reads the property of `x` (a vertex or edge) and writes it to the output iterator: `*out++ = get(pa, x)`.

property_writer(PropertyMap pa, OutputIterator out)

Constructs a writer reading from the property map pa and writing to out.

void operator()(T x, Graph& g)

Reads the property of x (a vertex or edge) and writes it to the output iterator: *out++ = get(pa, x).

Non-Member Functions

Function Description

Function	Description
`write_property(PropertyMap pa, OutputIterator out, EventTag)`	Convenience factory that creates a `property_writer`.

write_property(PropertyMap pa, OutputIterator out, EventTag)

Convenience factory that creates a property_writer.

Example

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/breadth_first_search.hpp>
#include <boost/graph/visitors.hpp>
#include <iostream>
#include <iterator>

int main() {
    using namespace boost;
    using Graph = adjacency_list<vecS, vecS, undirectedS>;

    Graph g(5);
    add_edge(0, 1, g);
    add_edge(0, 2, g);
    add_edge(1, 3, g);
    add_edge(2, 4, g);

    // Print vertex indices as they are discovered
    std::ostream_iterator<int> out(std::cout, " ");
    auto vis = make_bfs_visitor(
        write_property(get(vertex_index, g), out, on_discover_vertex())
    );

    std::cout << "BFS discovery order: ";
    breadth_first_search(g, vertex(0, g), visitor(vis));
    std::cout << "\n";
}

BFS discovery order: 0 1 2 3 4

Edit this Page