property_put

Writes a fixed value to a property map when a vertex or edge is visited at an event point. Useful as an alternative to an explicit loop for initializing a property map, or to mark a subset of vertices or edges (for example, only back edges) during a search.

Defined in: <boost/graph/visitors.hpp>
Models: EventVisitor
Typical event: any (vertex or 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 EventTag>
struct property_put {
  typedef EventTag event_filter;
  property_put(PropertyMap pa,
               typename property_traits<PropertyMap>::value_type value);

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

template <typename PropertyMap, typename EventTag>
property_put<PropertyMap, EventTag>
put_property(PropertyMap pa,
             typename property_traits<PropertyMap>::value_type value,
             EventTag);

Template Parameters

Parameter Description

Parameter	Description
`PropertyMap`	A WritablePropertyMap whose key type is the graph’s vertex or edge descriptor (depending on the event tag).
`EventTag`	The event at which to write. May be any event, vertex or edge.

PropertyMap

A WritablePropertyMap whose key type is the graph’s vertex or edge descriptor (depending on the event tag).

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_put(PropertyMap pa, value_type value)`	Constructs a visitor that writes the fixed `value` into the property map `pa`.
`void operator()(VertexOrEdge x, const Graph& g)`	Writes the fixed value into the property map for `x` (a vertex or edge): `put(pa, x, value)`.

property_put(PropertyMap pa, value_type value)

Constructs a visitor that writes the fixed value into the property map pa.

void operator()(VertexOrEdge x, const Graph& g)

Writes the fixed value into the property map for x (a vertex or edge): put(pa, x, value).

Non-Member Functions

Function Description

Function	Description
`put_property(PropertyMap pa, value_type value, EventTag)`	Convenience factory that creates a `property_put`.

put_property(PropertyMap pa, value_type value, EventTag)

Convenience factory that creates a property_put.

Example

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/depth_first_search.hpp>
#include <boost/graph/visitors.hpp>
#include <boost/property_map/property_map.hpp>
#include <iostream>
#include <vector>

int main() {
    using namespace boost;
    using Graph = adjacency_list<vecS, vecS, directedS,
        no_property, property<edge_index_t, int>>;
    using Edge = graph_traits<Graph>::edge_descriptor;

    Graph g(4);
    add_edge(0, 1, 0, g);
    add_edge(1, 2, 1, g);
    add_edge(2, 0, 2, g);  // creates a back edge
    add_edge(1, 3, 3, g);

    // Mark back edges with true using property_put
    std::vector<bool> is_back(num_edges(g), false);
    auto edge_id = get(edge_index, g);
    auto back_map = make_iterator_property_map(is_back.begin(), edge_id);

    auto vis = make_dfs_visitor(
        put_property(back_map, true, on_back_edge())
    );
    depth_first_search(g, visitor(vis));

    for (auto ei = edges(g).first; ei != edges(g).second; ++ei) {
        Edge e = *ei;
        std::cout << source(e, g) << " -> " << target(e, g);
        if (is_back[get(edge_id, e)]) {
            std::cout << "  [back edge]";
        }
        std::cout << "\n";
    }
}

0 -> 1
1 -> 2
1 -> 3
2 -> 0  [back edge]

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