Boost图clear_out_edges参数失配

Question

根据list.html

clear_out_edges的声明是：

void clear_out_edges(vertex_descriptor u, adjacency_list& g)

我的档案里有以下内容：

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;

在试图通过以下方式访问所有顶点来清除边缘时：

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adjacency_list类的对象。

任何帮助都是非常感谢的。

Answer 1

您正在使用v，就好像它是一个描述符，但它是一个迭代器。销毁它：

clear_out_edges(*v, g);

我可以建议稍微现代化一点，或者使用捆绑的属性和更少的using namespace吗？太多的代码被复制粘贴在古代的文档样本中，而这些样本被写成仍然可以在c++03上编译。

在Wandbox上直播

#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);
    }
}

甚至更好，取决于口味。请注意，至少vertex_index与vecS是非常冗余的，并且可能会严重损害您的代码正确性。

更新

一些关于代码现代化的提示，也许还可以将图形模型与特定于算法的元数据分离开来。

在Wandbox上直播

#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存在一个已知的问题(请参阅Boost max流算法不编译。错误:形成对空的引用和https://github.com/boostorg/graph/issues/232)。