How to use boost make_label_writer to write edge properties? - c++

Question

I have a simple graph, I suceeded writing properties with the vertex, but when I use make_label_writer to write properties to the edges, the complier always complains. Could someone help with it?
My code is as following:
int main (int argc, char * argv[]) {
typedef std::pair<int ,int> Edge;
std::vector<Edge> used_by = {Edge(1, 0), Edge(2, 1),
Edge(1,2), Edge(2, 0)};
using namespace boost;
typedef adjacency_list<vecS, vecS, directedS
> Graph;
Graph g(used_by.begin(), used_by.end(), 3);
std::ofstream dmp;
dmp.open("dmp.dot");
//name for vertex
std::vector<std::string> name{"one", "two", "three"};
//name for edge
std::vector<std::string> name1{"e1", "e2", "e3", "e4"};
write_graphviz(std::cout, g, make_label_writer(&name[0])
,make_label_writer(&name1[0]));
}
The write_graphviz() will ofc called the template, which is perfectly fine :
template <typename Graph, typename VertexWriter, typename
EdgeWriter>
inline void
write_graphviz(std::ostream& out, const Graph& g,
VertexWriter vw, EdgeWriter ew
BOOST_GRAPH_ENABLE_IF_MODELS_PARM(Graph,vertex_list_graph_tag))
{
default_writer gw;
write_graphviz(out, g, vw, ew, gw);
}
So the problem is now: when I only write the vertex properties using make_label_writer(&name[0]]]), the code runs perfectly. But when I add make_label_writer(&name1[0]), there is error.

Answer 1

The default vertex index is integral, which is why you can use the address of the first vertex name as implied associative property map.
The edge descriptor is a different beast and requires you to either
create an explicit iterator property map (using an extra index property map to map from edge descriptor to the integral index into the name1 vector)
or use a model of the Associative PropertyMap concept.
In this case you should property do the later using a std::map<edge_descriptor, std::string>.
Please also consider making your life with properties a lot simpler by using Bundled Properties.
Associative Property Map
Live On Coliru
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/graphviz.hpp>
typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::directedS> Graph;
int main() {
Graph g(3);
auto e1 = add_edge(1, 0, g).first;
auto e2 = add_edge(2, 1, g).first;
auto e3 = add_edge(1, 2, g).first;
auto e4 = add_edge(2, 0, g).first;
std::vector<std::string> vname{ "one", "two", "three" };
std::map<Graph::edge_descriptor, std::string> ename{
{ e1, "e1" },
{ e2, "e2" },
{ e3, "e3" },
{ e4, "e4" },
};
write_graphviz(std::cout, g,
boost::make_label_writer(&vname[0]),
make_label_writer(boost::make_assoc_property_map(ename)));
}
Prints
Bundled Properties Instead
Live On Coliru
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/graphviz.hpp>
struct VertexProps { std::string name; };
struct EdgeProps { std::string name; };
typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::directedS, VertexProps, EdgeProps> Graph;
int main() {
Graph g(3);
g[0].name = "one";
g[1].name = "two";
g[2].name = "three";
add_edge(1, 0, {"e1"}, g);
add_edge(2, 1, {"e2"}, g);
add_edge(1, 2, {"e3"}, g);
add_edge(2, 0, {"e4"}, g);
write_graphviz(std::cout, g,
make_label_writer(get(&VertexProps::name, g)),
make_label_writer(get(&EdgeProps::name, g)));
}
Prints the same