What is a Simple Example for using the Boost Graph Library - c++

Question

I am trying to use the BGL, I find the documentation precise but lacks more examples for simple cases. My goal is described below (after reading the documentation I still couldn't do this):
struct Vertex
{
double m_d;
std::size_t m_id;
};
//or
struct Vertex
{
double m_d;
std::size_t id() const;
};
Goals:
A directed graph G (what is the difference between a bidirectional and directed other than in_edges please?)
G can hold the vertex type Vertex.
get the vertex by id from G and change the value m_d in the Vertex struct when I want.
add, remove verticies and edges between verticies and also supports costs i.e. cost(edge).
Could you please write me an example on how to do this with BGL please? I beleive I need MutableBidirectionalGraph?

Answer 1

A directed graph G
Straight-away:
struct Vertex {
double m_d = 0;
size_t m_id = -1;
// or std::size_t id() const;
};
struct Edge {
double cost = 0;
};
using Graph =
boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS, Vertex, Edge>;
(what is the difference between a bidirectional and directed other than
in_edges please?)
There is no other difference, except of course the complexity guarantees
for enumerating incoming edges, and a linear overhead upon insertion of edges
G can hold the vertex type Vertex.
See 0.
get the vertex by id from G
auto find_by_id = [&g](size_t id) -> Vertex& {
auto vv = boost::make_iterator_range(vertices(g));
auto vd = find_if(vv, [&, id](auto vd) { return g[vd].m_id == id; });
return g[*vd];
};
and change the value m_d in the Vertex struct when I want.
if (i_want()) {
g[vd].m_id += 1;
}
Or,
auto idmap = boost::get(&Vertex::m_id, g);
if (i_want()) {
idmap[vd] += 1;
}
or even
put(idmap, vd, 42);
or even more unmarked:
get(boost::vertex_bundle, g, vd).m_id = 999;
add, remove vertices
remove_vertex(vd, g);
and edges between vertices
clear_vertex(vd, g);
and also supports costs i.e. cost(edge).
Wow that really has nothing to do with any of the above. But it's really the same as with vertex ids:
if (i_want()) {
g[ed].cost = new_cost;
}
Or,
auto cost = boost::get(&Edge::cost, g);
if (i_want()) {
cost[ed] = new_cost;
}
or even
put(cost, ed, new_cost);
or even more unmarked:
get(boost::edge_bundle, g, ed).cost = new_cost;
Live Demo
Live On Coliru
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/graph_utility.hpp>
#include <boost/range/algorithm.hpp>
#include <iostream>
struct Vertex {
double m_d = 0;
size_t m_id = -1;
// or std::size_t id() const;
};
struct Edge {
double cost = 0;
};
using Graph =
boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS, Vertex, Edge>;
using boost::make_iterator_range;
int main(){
Graph g;
auto v0 = add_vertex({0.1, 100}, g);
auto v1 = add_vertex({0.2, 200}, g);
auto v2 = add_vertex({0.3, 300}, g);
auto v3 = add_vertex({0.4, 400}, g);
auto v4 = add_vertex({0.5, 500}, g);
auto v5 = add_vertex({0.6, 600}, g);
add_edge(v0, v2, Edge{1.5}, g);
add_edge(v1, v3, Edge{2.5}, g);
add_edge(v4, v1, Edge{3.5}, g);
add_edge(v2, v5, Edge{4.5}, g);
auto idmap = boost::get(&Vertex::m_id, g);
auto cost = boost::get(&Edge::cost, g);
auto find_by_id = [&g](size_t id) -> Vertex& {
auto vv = boost::make_iterator_range(vertices(g));
auto vd = find_if(vv, [&, id](auto vd) { return g[vd].m_id == id; });
return g[*vd];
};
print_graph(g, idmap, std::cout << "original: ");
auto i_want = [](auto vd) {
return (vd % 2); // when I want
};
for (auto vd : make_iterator_range(vertices(g))) {
if (i_want(vd))
g[vd].m_id += 1;
if (i_want(vd))
idmap[vd] += 1;
//put(idmap, vd, 42);
//get(boost::vertex_bundle, g, vd).m_id = 999;
}
print_graph(g, idmap, std::cout << "altered: ");
clear_vertex(v3, g);
remove_vertex(v3, g); // undefined behaviour unless edges cleared
print_graph(g, idmap, std::cout << "removed: ");
for (auto ed : make_iterator_range(edges(g))) {
std::cout << ed << " cost " << cost[ed] << "\n";
}
for (auto ed : make_iterator_range(edges(g))) {
cost[ed] *= 111;
}
for (auto ed : make_iterator_range(edges(g))) {
std::cout << ed << " cost " << cost[ed] << "\n";
}
};
Prints
original: 100 --> 300
200 --> 400
300 --> 600
400 -->
500 --> 200
600 -->
altered: 100 --> 300
202 --> 402
300 --> 602
402 -->
500 --> 202
602 -->
removed: 100 --> 300
202 -->
300 --> 602
500 --> 202
602 -->
(0,2) cost 1.5
(3,1) cost 3.5
(2,4) cost 4.5
(0,2) cost 166.5
(3,1) cost 388.5
(2,4) cost 499.5