Boost Graph Library: checking whether a graph is directed or not

Question

I am writing a function that performs some calculation on graphs using the BGL. The way the calculation is done depends on whether the graph is directed or not, but I would like to avoid writing two different functions, one for undirected graphs and one for directed graphs. Both types of graph are defined as follows

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

Is there a way to check whether a graph is directed or not from the graph object itself? In other words, is there a way to know, from the graph object, the "directedness" property used (i.e., undirectedS, bidiretionalS or directedS)?

JosephD · Accepted Answer · 2016-05-31T12:45:18.733

I found the answer while looking at the definition of the function print_graph() in graph_utility.hpp, which led me to the function is_directed() defined in graph_traits.hpp.

I suppose there may be a more elegant way to do this, but here is a minimal working example:

#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;
}

which correctly returns

>> 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: checking whether a graph is directed or not

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