Issue with in_degree function

Question

I've troube using the in_degree function in boost graph. It fails with the following crytic message :

..\boost_lib\boost_1_66_0\boost\graph\detail\adjacency_list.hpp|1673|error: no matching function for call to 'in_edge_list(Graph&, void*&)'|

Why is vb of void*& type? It is supposed to be a vertex_descriptor.

Here a small example reproducing my issue :

#include <string>
#include <iostream>

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

//The typedef used
typedef boost::adjacency_list<
boost::setS, boost::setS, boost::directedS> graph;
typedef boost::graph_traits<graph>::vertex_descriptor Vertex;

int main()
{
    graph g(1);

    boost::graph_traits<graph>::vertex_iterator vb,ve;
    boost::tie(vb,ve)=boost::vertices(g);
    std::cout << boost::in_degree(*vb,g);
    return 0;
}

Answer 1

Why is vb of void*& type? It is supposed to be a vertex_descriptor.

And why shouldn't that descriptor be of void* type? That's exactly the type that it's defined to be.

error: no matching function for call to 'in_edge_list(Graph&, void*&)'

The problem is, there is no matching function call, because in_degree() isn't supposed to work on your graph. You can see what your graph supports here: http://www.boost.org/doc/libs/1_66_0/libs/graph/doc/graph_concepts.html

As you can see in_degree() requires the BidirectionalGraph concept.

You could be satisfied knowing just the out-degree:

std::cout << boost::out_degree(*vb, g);

Or you can switch to a BidirectionalGraph model:

Live On Coliru

#include <iostream>
#include <string>

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

typedef boost::adjacency_list<boost::setS, boost::setS, boost::bidirectionalS> graph;
typedef graph::vertex_descriptor Vertex;

int main() {
    graph g(1);

    boost::graph_traits<graph>::vertex_iterator vb, ve;
    boost::tie(vb, ve) = boost::vertices(g);

    std::cout << boost::out_degree(*vb, g) << std::endl;
    std::cout << boost::in_degree(*vb, g) << std::endl;
}

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