Boost graph: Iterating through all vertices and printing adjacent vertices - c++

Question

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;

Answer 1

Observations:
Where's the rest of the code? It obviously depends on the types used.
ai and a_end aren't initialized (perhaps you didn't actually mean the code doesn't compile, and this was your whole problem)
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:
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#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());
}
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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