使用 Boost，如何将自定义边缘属性作为结构放置/获取？

Question

我已经阅读了这里的文档 (https://www.boost.org/doc/libs/1_75_0/libs/graph/doc/using_adjacency_list.html) 和几个堆栈溢出页面两个小时，但这里根本没有取得任何进展。我有一个图表，其中边缘既有距离又有坑洞的数量（撞到 3 个坑洞后车辆会中断），所以我想我会使用自定义结构并设置边缘属性。

把它放在类声明的上方：

struct road_details_t {
  typedef boost::edge_property_tag kind;
};
struct road_info {
  unsigned miles;
  bool pothole;
};
typedef boost::property<road_details_t, struct road_info> RoadDetailsProperty;

编辑：我相信这是上述方法的替代方案，也没有运气：

namespace boost {
    enum road_details_t { road_details };
    BOOST_INSTALL_PROPERTY(edge, road_details);
}

类声明中的邻接图：

typedef boost::adjacency_list<boost::listS,       // store edges in lists
                              boost::vecS,        // store vertices in a vector
                              boost::undirectedS
                              RoadDetailsProperty
                              >
    Graph;
typedef boost::graph_traits<Graph> GraphTraits;
typedef GraphTraits::vertex_descriptor Vertex;
typedef GraphTraits::edge_descriptor Edge;

Graph roadMap;

稍后在一个函数中添加道路：

void City::addRoad(Intersection intersection1, Intersection intersection2, unsigned time, bool pothole) 
{
    unsigned nV = num_vertices(roadMap);
    while (intersection1 >= nV)
        nV = add_vertex(roadMap)+1;
    while (intersection2 >= nV)
        nV = add_vertex(roadMap)+1;
    add_edge(intersection1, intersection2, roadMap);

所以现在我正在尝试输入/获取道路信息，其中有多个错误，并且我尝试了很多变体：

// get the edge
std::pair<Edge, bool> edg = edge(intersection1, intersection2, roadMap);

// get the property map for road details. ERROR: no matching function call to get()
typename property_map<Graph, road_details_t>::type
  roadDetailMap = get(road_details_t(), roadMap);

// create struct from arguments passed in
struct road_info info = {time, pothole};

// attempt to add to roadDetailMap
put(roadDetailMap, edg, info);
// roadDetailMap[edg] = info; // also not working

// attempt to fetch information
cout << get(roadDetailMap, edg).miles << endl;
// cout << roadDetailMap[edg].miles << endl; // also not working

通过注释掉不同的行，我发现问题似乎在于我如何获取属性图，但是在网上查看示例时，我觉得我正在做与他们完全相同的事情。

目标最终只是弄清楚如何添加道路信息以及以后如何获取它，因此可以接受完全不同的方法，我这里的只是我尝试过（不成功）但我觉得取得了最有希望的结果。

Answer 1

您可以按照您的建议进行操作，这需要使用BOOST_INSTALL_PROPERTY 注册属性标签（请参阅example/examples/edge_property.cpp for an example）。相关sn-p：

namespace boost {
  enum edge_flow_t { edge_flow };
  enum edge_capacity_t { edge_capacity };

  BOOST_INSTALL_PROPERTY(edge, flow);
  BOOST_INSTALL_PROPERTY(edge, capacity);
}

现在您可以在属性定义中使用新的属性标签 就像您使用内置标签之一一样。

  typedef property<capacity_t, int> Cap;
  typedef property<flow_t, int, Cap> EdgeProperty;
  typedef adjacency_list<vecS, vecS, no_property, EdgeProperty> Graph;

但是，由于您的用例如此频繁，因此任何用户定义的结构都已经有一个内置标记：vertex_bundle_t 和 edge_bundle_t：

捆绑属性

这是一个使用它的示例。文档：https://www.boost.org/doc/libs/1_75_0/libs/graph/doc/bundles.html

Live On Coliru

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/graph_utility.hpp>

struct road_info {
    unsigned miles;
    bool     pothole;
};

using Graph  = boost::adjacency_list<boost::listS, boost::vecS,
                                    boost::undirectedS, road_info>;
using Vertex = Graph::vertex_descriptor;
using Edge   = Graph::edge_descriptor;

int main() {
    Graph roadMap;

    Vertex road1     = add_vertex(road_info{15, false}, roadMap);
    Vertex road2     = add_vertex(road_info{3, true}, roadMap);
    /*Vertex road3 =*/ add_vertex(road_info{27, false}, roadMap);

    add_edge(road1, road2, roadMap);

    print_graph(roadMap);

    auto bmap = get(boost::vertex_bundle, roadMap);

    for (Vertex v : boost::make_iterator_range(vertices(roadMap))) {
        road_info& bundle = bmap[v];
        // or even easier
        // road_info& info = roadMap[v];
        auto& [miles, pothole] = roadMap[v]; // c++17

        std::cout << "Vertex #" << v << " " << miles << " miles, "
                  << "pothole:" << std::boolalpha << pothole << "\n";
    }

    // individual maps
    auto miles_map = get(&road_info::miles, roadMap);
    auto poth_map = get(&road_info::pothole, roadMap);

    for (Vertex v : boost::make_iterator_range(vertices(roadMap))) {
        std::cout << "Vertex #" << v << " " << miles_map[v] << " miles, "
                  << "pothole:" << std::boolalpha << poth_map[v] << "\n";

        put(poth_map, v, false); // reset pothole
    }
}

打印

0 <--> 1 
1 <--> 0 
2 <--> 
Vertex #0 15 miles, pothole:false
Vertex #1 3 miles, pothole:true
Vertex #2 27 miles, pothole:false
Vertex #0 15 miles, pothole:false
Vertex #1 3 miles, pothole:true
Vertex #2 27 miles, pothole:false

更新：边缘捆绑

对于 cmets 来说，把它变成一个边缘束只是表面上的修改：

Live On Coliru

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/graph_utility.hpp>

struct road_info {
    unsigned miles;
    bool     pothole;
};

using Graph =
    boost::adjacency_list<boost::listS, boost::vecS, boost::undirectedS,
                          boost::no_property, road_info>;
using Vertex = Graph::vertex_descriptor;
using Edge   = Graph::edge_descriptor;

int main() {
    Graph roadMap(3);

    add_edge(0, 1, road_info{15, false}, roadMap);
    add_edge(1, 2, road_info{3, true}, roadMap);

    print_graph(roadMap);

    auto bmap = get(boost::edge_bundle, roadMap);

    for (Edge e : boost::make_iterator_range(edges(roadMap))) {
        road_info& bundle = bmap[e];
        // or even easier
        // road_info& info = roadMap[e];
        auto& [miles, pothole] = roadMap[e]; // c++17

        std::cout << "Edge " << e << " " << miles << " miles, "
                  << "pothole:" << std::boolalpha << pothole << "\n";
    }

    // individual maps
    auto miles_map = get(&road_info::miles, roadMap);
    auto poth_map = get(&road_info::pothole, roadMap);

    for (Edge e : boost::make_iterator_range(edges(roadMap))) {
        std::cout << "Edge " << e << " " << miles_map[e] << " miles, "
                  << "pothole:" << std::boolalpha << poth_map[e] << "\n";

        put(poth_map, e, false); // reset pothole
    }
}

印刷：

0 <--> 1 
1 <--> 0 2 
2 <--> 1 
Edge (0,1) 15 miles, pothole:false
Edge (1,2) 3 miles, pothole:true
Edge (0,1) 15 miles, pothole:false
Edge (1,2) 3 miles, pothole:true

对于受虐狂

如果您坚持，您当然可以安装属性标签。接触个别成员会很不舒服（并且可能效率低下），但你会这样做：

Live On Coliru

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/graph_utility.hpp>
#include <boost/property_map/transform_value_property_map.hpp>

struct road_info {
    unsigned miles;
    bool     pothole;
};

namespace boost {
    struct edge_road_info_t {};
    BOOST_INSTALL_PROPERTY(edge, road_info);
    static inline constexpr edge_road_info_t road_info{};
}

using Graph =
    boost::adjacency_list<boost::listS, boost::vecS, boost::undirectedS,
                          boost::no_property, 
                          boost::property<boost::edge_road_info_t, road_info> >;
using Vertex = Graph::vertex_descriptor;
using Edge   = Graph::edge_descriptor;

int main() {
    Graph roadMap(3);

    add_edge(0, 1, road_info{15, false}, roadMap);
    add_edge(1, 2, road_info{3, true}, roadMap);

    print_graph(roadMap);

    auto info_map = get(boost::road_info, roadMap);

    for (Edge e : boost::make_iterator_range(edges(roadMap))) {
        road_info& info = info_map[e];
        // or even easier
        // road_info& info = roadMap[e];
        auto& [miles, pothole] = info; // c++17

        std::cout << "Edge " << e << " " << miles << " miles, "
                  << "pothole:" << std::boolalpha << pothole << "\n";
    }

    // individual maps
    auto miles_map = boost::make_transform_value_property_map(
        std::mem_fn(&road_info::miles), info_map);
    auto poth_map = boost::make_transform_value_property_map(
        std::mem_fn(&road_info::pothole), info_map);

    for (Edge e : boost::make_iterator_range(edges(roadMap))) {
        std::cout << "Edge " << e << " " << miles_map[e] << " miles, "
                  << "pothole:" << std::boolalpha << poth_map[e] << "\n";

        put(poth_map, e, false); // reset pothole
    }
}

再次打印相同的输出。