Boost Graph Library：潜在的Bug

即使图中没有循环,BGL的depth_first_search算法有时会对访问者调用back_edge().根据后缘的定义,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“后缘”.我在这做错了吗？或者这是一个错误？

#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;
在Debian 2.6.32-34squeeze1上使用gcc 4.4.5使用Boost 1.42.0进行测试.

解决方法

您提交了一个错误,但您没有跟进.

不久之后,你得到了答案：

You are not initializing the vertex_index property of your graph. Try adding some code such as:

graph_traits::vertices_size_type i = 0;

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

我尝试了这个(修复拼写错误)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,i++);

  bool inserted;   
  tie(tuples::ignore,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”)