Question

我正在编写一个函数，使用BGL对图形执行一些计算。计算的方式取决于图形是否有定向，但我想避免编写两个不同的函数，一个用于无向图，一个用于有向图。两种类型的图都定义如下

using namespace boost;
// Undirected
typedef adjacency_list<listS, vecS, undirectedS> UGraph;
// Directed
typedef adjacency_list<listS, vecS, bidirectionalS> DGraph;

有没有办法从图形对象本身检查图形是否定向？换句话说，有没有办法从图形对象中知道所使用的“定向性”属性（即无向性，双向性或有向性）？

Answer 1

我在查看graph_utility.hpp中函数print_graph()的定义时找到了答案，这导致了graph_traits.hpp中定义的函数is_directed()。

我想可能有更优雅的方法来做到这一点，但这是一个最小的工作示例：

#include <iostream>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/graph_traits.hpp>


template <typename graph_t>
void print_directedness(graph_t &g)
{
  // Typedef of an object whose constructor returns "directedness" of the graph object.
  typedef typename boost::graph_traits<graph_t>::directed_category Cat;
  // The function boost::detail::is_directed() returns "true" if the graph object is directed.
  if(boost::detail::is_directed(Cat()))
    std::cout << "The graph is directed." << std::endl;
  else
    std::cout << "The graph is undirected." << std::endl;
}


int main()
{

  // Creates an undirected graph and tests whether it is directed of not.
  boost::adjacency_list< boost::setS, boost::vecS, boost::undirectedS > UnGraph;
  print_directedness(UnGraph);

  // Creates a directed graph and tests whether it is directed of not.
  boost::adjacency_list< boost::setS, boost::vecS, boost::directedS > DiGraph;
  print_directedness(DiGraph);

  // Creates a bidirectional graph and tests whether it is directed of not.
  boost::adjacency_list< boost::setS, boost::vecS, boost::bidirectionalS > BidiGraph;
  print_directedness(BidiGraph);

  return 0;
}

正确返回

>> g++ minimal_working_example.cpp -o minimal_working_example
>> ./minimal_working_example
The graph is undirected.
The graph is directed.
The graph is directed.

Boost Graph Library：检查图表是否有定向

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