CODEWITHSUNDEEP
c++boostgraphadjacency-list
Jamo
Jamo

Reputation: 57

Boost graph: Iterating through all vertices and printing adjacent vertices

I want to print all vertices with their adjacent vertices. I found some examples online on how to do that, yet it won't work for me. I am getting the error, that the ++ operator cannot be used on ai. Also I think it needs to be vertex_idMap[*ai] and not vertex_idMap[ai] but this prompts an error. Does anyone know why this is wrong?

typedef adjacency_list<vecS, listS, directedS, VertexIDPorperty, EdgeWeight> Graph;  //the type of g
graph_traits <Graph>::vertex_iterator i, end;
graph_traits <Graph>::adjacency_iterator ai, a_end;
for (boost::tie(i, end) = vertices(g); i != end; ++i) {
    std::cout << vertex_idMap[*i];
    for (; ai != a_end; ++ai) {   //the ++ai seems to be wrong?
        std::cout << vertex_idMap[ai];
        if (boost::next(ai) != a_end)
            std::cout << ", ";
    }
std::cout << std::endl;

Upvotes: 2

Views: 2195

Answers (1)

sehe
sehe

Reputation: 392843

Observations:

  1. Where's the rest of the code? It obviously depends on the types used.
  2. ai and a_end aren't initialized (perhaps you didn't actually mean the code doesn't compile, and this was your whole problem)
  3. vertex_idMap[ai] will not compile, as a vertex_iterator is not a valid vertex_descriptor

Here's a fixed example with the missing bits imagined:

Live On Coliru

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

using VertexIDPorperty = boost::property<boost::vertex_index_t, int>;
using EdgeWeight       = boost::property<boost::edge_weight_t, double>;
typedef boost::adjacency_list<boost::vecS, boost::listS, boost::directedS, VertexIDPorperty, EdgeWeight> Graph;

Graph sample();

int main() {
    Graph g = sample();
    auto vertex_idMap = get(boost::vertex_index, g);
    boost::graph_traits <Graph>::vertex_iterator i, end;
    boost::graph_traits <Graph>::adjacency_iterator ai, a_end;

    for (boost::tie(i, end) = vertices(g); i != end; ++i) {
        std::cout << vertex_idMap[*i] << ": ";

        for (boost::tie(ai, a_end) = adjacent_vertices(*i, g); ai != a_end; ++ai) {
            std::cout << vertex_idMap[*ai];
            if (boost::next(ai) != a_end)
                std::cout << ", ";
        }
        std::cout << std::endl;
    }
}

Implementing sample() to create a random graph:

#include <boost/graph/random.hpp>
#include <random>

Graph sample() {
    Graph g;
    std::mt19937 prng { std::random_device{}() };

    generate_random_graph(g, 10, 20, prng);
    int id = 0;
    for (auto vd : boost::make_iterator_range(vertices(g))) {
        put(boost::vertex_index, g, vd, ++id);
    }

    return g;
}

It prints something like:

1: 9, 9, 4
2: 6
3: 
4: 
5: 9, 9, 8, 9
6: 9, 3, 1
7: 2, 10
8: 6
9: 8
10: 7, 3, 8, 1, 4

Out Of The Box

Printing a graph can be done simpler:

#include <boost/graph/graph_utility.hpp>
// ...

int main() {
    print_graph(sample());
}

Live On Coliru

1 --> 
2 --> 3 10 9 6 6 10 
3 --> 8 
4 --> 
5 --> 4 
6 --> 1 5 8 
7 --> 4 9 2 2 1 
8 --> 6 
9 --> 5 7 
10 --> 7

Upvotes: 2

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