Boost graph clear_out_edges 参数不匹配

Question

根据https://www.boost.org/doc/libs/1_37_0/libs/graph/doc/adjacency_list.html

clear_out_edges的声明是：

void clear_out_edges(vertex_descriptor u, adjacency_list& g)

我的文件中有以下内容：

typedef adjacency_list<
    vecS, vecS, directedS,

    property<
    vertex_name_t, std::string,
    property<vertex_index_t, int,
    property<vertex_color_t, boost::default_color_type,
    property<vertex_distance_t, double,
    property<vertex_predecessor_t, Traits::edge_descriptor>
    > > > >,

    property<
    edge_index_t, int,
    property<edge_capacity_t, double,
    property<edge_weight_t, double,
    property<edge_residual_capacity_t, double,
    property<edge_reverse_t, Traits::edge_descriptor>
> > > > >
Graph;

Graph g;

试图通过访问所有顶点来清除边缘：

Graph::vertex_iterator v, vend;
for(boost::tie(v, vend) = vertices(g); v != vend; ++v){
    boost::clear_out_edges(v, g);//line in question
}

编译器抱怨：

no instance of overloaded function "boost::clear_out_edges" matches the argument list -- argument types are: (boost::range_detail::integer_iterator<std::size_t>, Graph)C/C++(304)

我对此感到惊讶，因为 g 是通过 typedef 的 adjacency_list 类的对象。

感谢任何帮助。

Answer 1

您使用 v 就好像它是一个描述符，但它是一个迭代器。取消引用它：

clear_out_edges(*v, g);

我可以建议稍微现代化一下，也许使用捆绑属性而不是using namespace？从古老的文档样本中复制粘贴了太多代码，这些样本仍然可以在 c++03 上编译。

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#include <boost/graph/adjacency_list.hpp>
using namespace boost;

using Traits = adjacency_list_traits<vecS, vecS, directedS>;
using Graph  = adjacency_list<
    vecS, vecS, directedS,

    property<vertex_name_t, std::string,
    property<vertex_index_t, int,
    property<vertex_color_t, boost::default_color_type,
    property<vertex_distance_t, double,
    property<vertex_predecessor_t,
     Traits::edge_descriptor>>>>>,

    property<edge_index_t, int,
    property<edge_capacity_t, double,
    property<edge_weight_t, double,
    property<edge_residual_capacity_t, double,
    property<edge_reverse_t,
     Traits::edge_descriptor>>>>>>;

int main()
{
    Graph g(10);
    for (auto v : boost::make_iterator_range(vertices(g))) {
        clear_out_edges(v, g);
    }
}

或者更好，取决于口味。请注意，至少vertex_index 与vecS 是非常多余的，并且可能会严重损害您的代码正确性。

更新

关于现代化代码的一些提示，以及可能将图形模型与算法特定的元数据分开。

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#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/edmonds_karp_max_flow.hpp>
#include <boost/graph/boykov_kolmogorov_max_flow.hpp>

struct VertexProps { std::string name; };
struct EdgeProps { double capacity = 0, weight = 0, residual = 0; };

using Graph = boost::adjacency_list<boost::vecS, boost::vecS, boost::directedS,
                                    VertexProps, EdgeProps>;

using V = Graph::vertex_descriptor;
using E = Graph::edge_descriptor;

int main()
{
    Graph g(10);
    for (auto v : boost::make_iterator_range(vertices(g))) {
        clear_out_edges(v, g);
    }

    auto idmap = get(boost::vertex_index, g);
    std::vector<boost::default_color_type> colors(num_vertices(g));
    std::vector<E> predecessors(num_vertices(g));
    std::vector<double> distances(num_vertices(g));

    auto weightmap = get(&EdgeProps::weight, g);
    auto capacity_map = get(&EdgeProps::capacity, g);
    auto residual_map = get(&EdgeProps::residual, g);

    std::map<E, E> reverse_edges;

    V src  = 0;
    V sink = 1;

    boost::edmonds_karp_max_flow(
        g, src, sink,
        boost::color_map(colors.data())
            .vertex_index_map(idmap)
            .distance_map(distances.data())
            .predecessor_map(predecessors.data())
            .weight_map(weightmap)
            .capacity_map(capacity_map)
            .residual_capacity_map(residual_map)
            .reverse_edge_map(boost::make_assoc_property_map(reverse_edges)));
}

请记住，boykov_kolmogorov_max_flow 存在一个已知问题（请参阅 Boost max flow algorithms do not compile. error: forming reference to void 和 https://github.com/boostorg/graph/issues/232）。