c++ - 如何在boost中遍历图使用BFS

Question

我在编译一个非常简单的图的 BFS 时遇到了问题。无论我做什么，我都会收到关于不匹配方法调用的各种编译器消息(我已经尝试过 boost::visitor 和扩展 boost::default_bfs_visitor 等)

#include <stdint.h>
#include <iostream>
#include <vector>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/breadth_first_search.hpp>

int main() {
  typedef boost::adjacency_list<boost::vecS, boost::hash_setS, boost::undirectedS, uint32_t, uint32_t, boost::no_property> graph_t;
  graph_t graph(4);
  graph_t::vertex_descriptor a = boost::vertex(0, graph);
  graph_t::vertex_descriptor b = boost::vertex(1, graph);
  graph_t::vertex_descriptor c = boost::vertex(2, graph);
  graph_t::vertex_descriptor d = boost::vertex(3, graph);
  graph[a] = 0;
  graph[b] = 1;
  graph[c] = 2;
  graph[d] = 3;
  std::pair<graph_t::edge_descriptor, bool> result = boost::add_edge(a, b, 0, graph);
  result = boost::add_edge(a, c, 1, graph);
  result = boost::add_edge(c, b, 2, graph);
  class {
  public:
    void initialize_vertex(const graph_t::vertex_descriptor &s, graph_t &g) {
      std::cout << "Initialize: " << g[s] << std::endl;
    }
    void discover_vertex(const graph_t::vertex_descriptor &s, graph_t &g) {
      std::cout << "Discover: " << g[s] << std::endl;
    }
    void examine_vertex(const graph_t::vertex_descriptor &s, graph_t &g) {
      std::cout << "Examine vertex: " << g[s] << std::endl;
    }
    void examine_edge(const graph_t::edge_descriptor &e, graph_t &g) {
      std::cout << "Examine edge: " << g[e] << std::endl;
    }
    void tree_edge(const graph_t::edge_descriptor &e, graph_t &g) {
      std::cout << "Tree edge: " << g[e] << std::endl;
    }
    void non_tree_edge(const graph_t::edge_descriptor &e, graph_t &g) {
      std::cout << "Non-Tree edge: " << g[e] << std::endl;
    }
    void gray_target(const graph_t::edge_descriptor &e, graph_t &g) {
      std::cout << "Gray target: " << g[e] << std::endl;
    }
    void black_target(const graph_t::edge_descriptor &e, graph_t &g) {
      std::cout << "Black target: " << g[e] << std::endl;
    }
    void finish_vertex(const graph_t::vertex_descriptor &s, graph_t &g) {
      std::cout << "Finish vertex: " << g[s] << std::endl;
    }
  } bfs_visitor;
  boost::breadth_first_search(graph, a, bfs_visitor);
  return 0;
}

如何使用bfs_visitor访问图表？

附言。我看过并编译了"How to create a C++ Boost undirected graph and traverse it in depth first search (DFS) order?"但它没有帮助。

Answer 1

可以看到here breadth_first_search 的重载列表。如果您不想指定您需要使用命名参数版本的每一个参数。它看起来像这样:

breadth_first_search(graph, a, boost::visitor(bfs_visitor));

如果您在图形定义中使用 vecS 作为 VertexList 存储，或者如果您构建并初始化了一个内部 vertex_index 属性映射，这将按原样工作。由于您使用的是 hash_setS，因此您需要将调用更改为:

breath_first_search(graph, a, boost::visitor(bfs_visitor).vertex_index_map(my_index_map));

您已经在 uint32_t 捆绑属性中使用索引映射。您可以使用 get(boost::vertex_bundle, graph) 来访问它。

您的访问者也有问题。您应该从 boost::default_bfs_visitor 派生它，并且您的成员函数的 graph_t 参数需要是 const 限定的。

完整代码:

#include <stdint.h>
#include <iostream>
#include <vector>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/breadth_first_search.hpp>

typedef boost::adjacency_list<boost::vecS, boost::hash_setS, boost::undirectedS, uint32_t, uint32_t, boost::no_property> graph_t;


struct my_visitor : boost::default_bfs_visitor{

    void initialize_vertex(const graph_t::vertex_descriptor &s, const graph_t &g) const {
      std::cout << "Initialize: " << g[s] << std::endl;
    }
    void discover_vertex(const graph_t::vertex_descriptor &s, const graph_t &g) const {
      std::cout << "Discover: " << g[s] << std::endl;
    }
    void examine_vertex(const graph_t::vertex_descriptor &s, const graph_t &g) const {
      std::cout << "Examine vertex: " << g[s] << std::endl;
    }
    void examine_edge(const graph_t::edge_descriptor &e, const graph_t &g) const {
      std::cout << "Examine edge: " << g[e] << std::endl;
    }
    void tree_edge(const graph_t::edge_descriptor &e, const graph_t &g) const {
      std::cout << "Tree edge: " << g[e] << std::endl;
    }
    void non_tree_edge(const graph_t::edge_descriptor &e, const graph_t &g) const {
      std::cout << "Non-Tree edge: " << g[e] << std::endl;
    }
    void gray_target(const graph_t::edge_descriptor &e, const graph_t &g) const {
      std::cout << "Gray target: " << g[e] << std::endl;
    }
    void black_target(const graph_t::edge_descriptor &e, const graph_t &g) const {
      std::cout << "Black target: " << g[e] << std::endl;
    }
    void finish_vertex(const graph_t::vertex_descriptor &s, const graph_t &g) const {
      std::cout << "Finish vertex: " << g[s] << std::endl;
    }
  };

int main() {
  graph_t graph(4);
  graph_t::vertex_descriptor a = boost::vertex(0, graph);
  graph_t::vertex_descriptor b = boost::vertex(1, graph);
  graph_t::vertex_descriptor c = boost::vertex(2, graph);
  graph_t::vertex_descriptor d = boost::vertex(3, graph);
  graph[a] = 0;
  graph[b] = 1;
  graph[c] = 2;
  graph[d] = 3;
  std::pair<graph_t::edge_descriptor, bool> result = boost::add_edge(a, b, 0, graph);
  result = boost::add_edge(a, c, 1, graph);
  result = boost::add_edge(c, b, 2, graph);

  my_visitor vis;

  breadth_first_search(graph, a, boost::visitor(vis).vertex_index_map(get(boost::vertex_bundle,graph)));
  return 0;
}