CODEWITHSUNDEEP
c++boostgraph
Mohannad
Mohannad

Reputation: 113

Boost graph conversion error

I'm creating a simple graph using boost library, and trying to iterate over the vertices and edges. But I'm receiving following error, where the code can iterate over all vertices but there is a compilation problem when I added the last segment of code which responsible for iterating over edges:

error: conversion from ‘std::pair, boost::detail::out_edge_iter >, long unsigned int, boost::detail::edge_desc_impl, long int>, boost::adjacency_list >, boost::detail::adj_list_edge_iterator, boost::detail::out_edge_iter >, long unsigned int, boost::detail::edge_desc_impl, long int>, boost::adjacency_list > >’ to non-scalar type ‘std::pair, boost::detail::out_edge_iter<__gnu_cxx::__normal_iterator*, std::vector, std::allocator > > >, long unsigned int, boost::detail::edge_desc_impl, long int>, boost::adjacency_list<> >, boost::detail::adj_list_edge_iterator, boost::detail::out_edge_iter<__gnu_cxx::__normal_iterator*, std::vector, std::allocator > > >, long unsigned int, boost::detail::edge_desc_impl, long int>, boost::adjacency_list<> > >’ requested boost::adjacency_list<>::edge_iterator> es = boost::edges(g);

Here is my code 

#include <iostream>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/graphviz.hpp>
int main()
{
    using namespace std;
    using namespace boost;

   typedef adjacency_list< listS, vecS, directedS > digraph;

   // instantiate a digraph object with 8 vertices
   digraph g(8);

   // add some edges
   add_edge(0, 1, g);
   add_edge(1, 5, g);
   add_edge(5, 6, g);
   add_edge(2, 3, g);
   add_edge(2, 4, g);
   add_edge(3, 5, g);
   add_edge(4, 5, g);
   add_edge(5, 7, g);

   // represent graph in DOT format and send to cout
   write_graphviz(cout, g);


   std::cout<< "+++++++++++++++++++++++++++++++++++++\n";
   std::cout<<"Print Vertices\n";

   std::pair<boost::adjacency_list<>::vertex_iterator,
      boost::adjacency_list<>::vertex_iterator> vs = boost::vertices(g);

    std::copy(vs.first, vs.second,std::ostream_iterator<boost::adjacency_list<>::vertex_descriptor>{
        std::cout, "\n"});


    std::cout<< "+++++++++++++++++++++++++++++++++++++\n";
    std::cout<<"Print Edges\n";

    std::pair<boost::adjacency_list<>::edge_iterator,
        boost::adjacency_list<>::edge_iterator> es = boost::edges(g);

      std::copy(es.first, es.second,std::ostream_iterator<boost::adjacency_list<>::edge_descriptor>{
          std::cout, "\n"});

   return 0;
}

Upvotes: 2

Views: 379

Answers (1)

Alex
Alex

Reputation: 790

You're assigning the result of edges to a variable of incompatible type. Instead of

std::pair<boost::adjacency_list<>::edge_iterator,
    boost::adjacency_list<>::edge_iterator> es = boost::edges(g);

use

auto es = boost::edges(g);

or

std::pair<digraph::edge_iterator, digraph::edge_iterator> es = boost::edges(g);

More details: your type digraph specifies three template arguments for adjacency_list:

typedef adjacency_list< listS, vecS, directedS > digraph;

You call edges with an argument of this type, but you specify that the function's EdgeIterator template parameter must be boost::adjacency_list<>::edge_iterator, as if g were of type adjacency_list<> instead of adjacency_list<listS, vecS, directedS>. Apparently the conversion is valid for adjacency_list<>::vertex_iterator but not adjacency_list<>::edge_iterator.

Upvotes: 4

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