Boost Graph Library:潜在的Bug

时间:2011-08-13 00:22:15

标签: boost graph visitor boost-graph

BGL的depth_first_search算法有时会对访问者调用back_edge(),即使图中没有循环也是如此。根据后边缘的定义,根据Boost的DFS Visitor Documentation,这不应该发生。请注意,仅当listS用作顶点和边的表示时,这才是可重现的。

下面的代码示例(应该按原样编译)构造一个包含两个节点和一个边的图。它错误地打印“后边缘”。我在这里做错了吗?或者这是一个错误吗?

#include <iostream>
using namespace std;

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

typedef boost::property<boost::vertex_index_t,std::size_t> VertexProperties;
typedef boost::adjacency_list<boost::listS,
                              boost::listS,
                              boost::bidirectionalS,
                              VertexProperties> Graph;  // Graph object type

typedef boost::graph_traits<Graph>::vertex_descriptor Vertex;
typedef boost::graph_traits<Graph>::edge_descriptor Edge;

class VisitorClass : public dfs_visitor<> {
 public:
  VisitorClass() {}

  template <typename Edge, typename Graph>
  void back_edge(Edge, const Graph&) const {
    cout << "back edge" << endl;
  }
};

int
main() {
  Graph g;
  Vertex v = add_vertex(g);
  Vertex u = add_vertex(g);

  bool inserted;
  tie(tuples::ignore, inserted) = add_edge(v, u, g);
  assert(inserted);

  VisitorClass vst;
  depth_first_search(g, visitor(vst));
  // Should not print "back edge", but does.

  return 0;
}

在Mac OS 10.7上使用i686-apple-darwin11-llvm-g ++ - 4.2测试Boost 1.46.1;
使用Debian 2.6.32-34squeeze1上的gcc 4.4.5测试Boost 1.42.0。

1 个答案:

答案 0 :(得分:4)

您提交了一个错误,但您没有跟进。

不久之后,你得到了答案:

  

您没有初始化图表的vertex_index属性。尝试添加一些代码,例如:

     
    

graph_traits :: vertices_size_type i = 0;

         

BGL_FORALL_VERTICES(v,graph,Graph)put(vertex_index,g,v,i ++);

  

我试过这个(修正错字)并且工作正常:

#include <boost/graph/iteration_macros.hpp>

int main() {
  Graph g;   
  Vertex v = add_vertex(g);   
  Vertex u = add_vertex(g);

  graph_traits<Graph>::vertices_size_type i = 0;  
  BGL_FORALL_VERTICES(v, g, Graph) put(vertex_index, g, v, i++);

  bool inserted;   
  tie(tuples::ignore, inserted) = add_edge(v, u, g); 
  assert(inserted);

  VisitorClass vst;   
  depth_first_search(g, visitor(vst));
// Should not print "back edge", but does.

  return 0;
  }

(至少,它不再打印“后缘”)