How to traverse graph in boost use BFS - c++

Question

I have problems getting to compile the BFS of a very simple graph. Whatever I do I get various compiler messages about unmatched method calls (I've tried boost::visitor and extending boost::default_bfs_visitor etc.)
#include <stdint.h>
#include <iostream>
#include <vector>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/breadth_first_search.hpp>
int main() {
typedef boost::adjacency_list<boost::vecS, boost::hash_setS, boost::undirectedS, uint32_t, uint32_t, boost::no_property> graph_t;
graph_t graph(4);
graph_t::vertex_descriptor a = boost::vertex(0, graph);
graph_t::vertex_descriptor b = boost::vertex(1, graph);
graph_t::vertex_descriptor c = boost::vertex(2, graph);
graph_t::vertex_descriptor d = boost::vertex(3, graph);
graph[a] = 0;
graph[b] = 1;
graph[c] = 2;
graph[d] = 3;
std::pair<graph_t::edge_descriptor, bool> result = boost::add_edge(a, b, 0, graph);
result = boost::add_edge(a, c, 1, graph);
result = boost::add_edge(c, b, 2, graph);
class {
public:
void initialize_vertex(const graph_t::vertex_descriptor &s, graph_t &g) {
std::cout << "Initialize: " << g[s] << std::endl;
}
void discover_vertex(const graph_t::vertex_descriptor &s, graph_t &g) {
std::cout << "Discover: " << g[s] << std::endl;
}
void examine_vertex(const graph_t::vertex_descriptor &s, graph_t &g) {
std::cout << "Examine vertex: " << g[s] << std::endl;
}
void examine_edge(const graph_t::edge_descriptor &e, graph_t &g) {
std::cout << "Examine edge: " << g[e] << std::endl;
}
void tree_edge(const graph_t::edge_descriptor &e, graph_t &g) {
std::cout << "Tree edge: " << g[e] << std::endl;
}
void non_tree_edge(const graph_t::edge_descriptor &e, graph_t &g) {
std::cout << "Non-Tree edge: " << g[e] << std::endl;
}
void gray_target(const graph_t::edge_descriptor &e, graph_t &g) {
std::cout << "Gray target: " << g[e] << std::endl;
}
void black_target(const graph_t::edge_descriptor &e, graph_t &g) {
std::cout << "Black target: " << g[e] << std::endl;
}
void finish_vertex(const graph_t::vertex_descriptor &s, graph_t &g) {
std::cout << "Finish vertex: " << g[s] << std::endl;
}
} bfs_visitor;
boost::breadth_first_search(graph, a, bfs_visitor);
return 0;
}
How to visit the graph using bfs_visitor?
PS. I've seen and compiled "How to create a C++ Boost undirected graph and traverse it in depth first search (DFS) order?" but it didn't help.

Answer 1

You can see here a list of the overloads of breadth_first_search. If you don't want to specify every one of the parameters you need to use the named-parameter version. It would look like this:
breadth_first_search(graph, a, boost::visitor(bfs_visitor));
This would work as is if you had used vecS as your VertexList storage in your graph definition or if you had constructed and initialized an internal vertex_index property map. Since you are using hash_setS you need to change the invocation to:
breath_first_search(graph, a, boost::visitor(bfs_visitor).vertex_index_map(my_index_map));
You are already using an index map in your uint32_t bundled property. You can use get(boost::vertex_bundle, graph) to access it.
There was also a problem with your visitor. You should derive it from boost::default_bfs_visitor and the graph_t parameter of your member functions needs to be const qualified.
Full code:
#include <stdint.h>
#include <iostream>
#include <vector>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/breadth_first_search.hpp>
typedef boost::adjacency_list<boost::vecS, boost::hash_setS, boost::undirectedS, uint32_t, uint32_t, boost::no_property> graph_t;
struct my_visitor : boost::default_bfs_visitor{
void initialize_vertex(const graph_t::vertex_descriptor &s, const graph_t &g) const {
std::cout << "Initialize: " << g[s] << std::endl;
}
void discover_vertex(const graph_t::vertex_descriptor &s, const graph_t &g) const {
std::cout << "Discover: " << g[s] << std::endl;
}
void examine_vertex(const graph_t::vertex_descriptor &s, const graph_t &g) const {
std::cout << "Examine vertex: " << g[s] << std::endl;
}
void examine_edge(const graph_t::edge_descriptor &e, const graph_t &g) const {
std::cout << "Examine edge: " << g[e] << std::endl;
}
void tree_edge(const graph_t::edge_descriptor &e, const graph_t &g) const {
std::cout << "Tree edge: " << g[e] << std::endl;
}
void non_tree_edge(const graph_t::edge_descriptor &e, const graph_t &g) const {
std::cout << "Non-Tree edge: " << g[e] << std::endl;
}
void gray_target(const graph_t::edge_descriptor &e, const graph_t &g) const {
std::cout << "Gray target: " << g[e] << std::endl;
}
void black_target(const graph_t::edge_descriptor &e, const graph_t &g) const {
std::cout << "Black target: " << g[e] << std::endl;
}
void finish_vertex(const graph_t::vertex_descriptor &s, const graph_t &g) const {
std::cout << "Finish vertex: " << g[s] << std::endl;
}
};
int main() {
graph_t graph(4);
graph_t::vertex_descriptor a = boost::vertex(0, graph);
graph_t::vertex_descriptor b = boost::vertex(1, graph);
graph_t::vertex_descriptor c = boost::vertex(2, graph);
graph_t::vertex_descriptor d = boost::vertex(3, graph);
graph[a] = 0;
graph[b] = 1;
graph[c] = 2;
graph[d] = 3;
std::pair<graph_t::edge_descriptor, bool> result = boost::add_edge(a, b, 0, graph);
result = boost::add_edge(a, c, 1, graph);
result = boost::add_edge(c, b, 2, graph);
my_visitor vis;
breadth_first_search(graph, a, boost::visitor(vis).vertex_index_map(get(boost::vertex_bundle,graph)));
return 0;
}

Answer 2

I faced the same problem, but compared to the answer provided by user1252091 my vertex type is a struct that doesn't include an integer that can be used to create a vertex_index_map, therefore the line
breadth_first_search(graph, a, boost::visitor(vis).vertex_index_map(get(boost::vertex_bundle,graph)));
wouldn't work in my case. Eventually I figured out how to create an external vertex_index_map (thanks also to this answer) and pass it to the breadth_first_search function. Here is a working example in case it helps others:
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/visitors.hpp>
#include <boost/graph/breadth_first_search.hpp>
#include <iostream>
struct Person
{
std::string Name;
unsigned int YearBorn;
};
typedef boost::adjacency_list <boost::vecS, boost::hash_setS, boost::bidirectionalS, Person, boost::no_property > FamilyTree;
typedef boost::graph_traits<FamilyTree>::vertex_descriptor Vertex;
typedef boost::graph_traits<FamilyTree>::edge_descriptor Edge;
template <class Graph>
class BfsVisitor : public boost::default_bfs_visitor
{
public:
typedef typename boost::graph_traits<Graph>::vertex_descriptor VertexDescriptor;
typedef typename boost::graph_traits<Graph>::edge_descriptor EdgeDescriptor;
BfsVisitor(std::vector<VertexDescriptor>& nodesVisited)
: m_nodesVisited(nodesVisited){}
void tree_edge(EdgeDescriptor e, const Graph& g) const
{
VertexDescriptor u = source(e, g);
VertexDescriptor v = target(e, g);
m_nodesVisited.push_back(v);
}
private:
std::vector<VertexDescriptor>& m_nodesVisited;
};
const Person Abe_Simpson {"Abe_Simpson", 0};
const Person Mona_Simpson { "Mona_Simpson", 0};
const Person Herb_Simpson { "Herb_Simpson", 0};
const Person Homer_Simpson { "Homer_Simpson", 0};
const Person Clancy_Bouvier { "Clancy_Bouvier", 0};
const Person Jacqueline_Bouvier { "Jacqueline_Bouvier", 0};
const Person Marge_Bouvier { "Marge_Bouvier", 0};
const Person Patty_Bouvier { "Patty_Bouvier", 0};
const Person Selma_Bouvier { "Selma_Bouvier", 0};
const Person Bart_Simpson { "Bart_Simpson", 0};
const Person Lisa_Simpson { "Lisa_Simpson", 0};
const Person Maggie_Simpson { "Maggie_Simpson", 0};
const Person Ling_Bouvier { "Ling_Bouvier", 0};
int main(void)
{
std::cout << __FUNCTION__ << "\n";
FamilyTree g;
// nodes
auto v_Abe_Simpson = boost::add_vertex(Abe_Simpson,g);
auto v_Mona_Simpson = boost::add_vertex(Mona_Simpson,g);
auto v_Herb_Simpson = boost::add_vertex(Herb_Simpson,g);
auto v_Homer_Simpson = boost::add_vertex(Homer_Simpson,g);
auto v_Clancy_Bouvier = boost::add_vertex(Clancy_Bouvier,g);
auto v_Jacqueline_Bouvier = boost::add_vertex(Jacqueline_Bouvier,g);
auto v_Marge_Bouvier = boost::add_vertex(Marge_Bouvier,g);
auto v_Patty_Bouvier = boost::add_vertex(Patty_Bouvier,g);
auto v_Selma_Bouvier = boost::add_vertex(Selma_Bouvier,g);
auto v_Bart_Simpson = boost::add_vertex(Bart_Simpson,g);
auto v_Lisa_Simpson = boost::add_vertex(Lisa_Simpson,g);
auto v_Maggie_Simpson = boost::add_vertex(Maggie_Simpson,g);
auto v_Ling_Bouvier = boost::add_vertex(Ling_Bouvier,g);
// connections
boost::add_edge(v_Abe_Simpson, v_Herb_Simpson, g);
boost::add_edge(v_Abe_Simpson, v_Homer_Simpson, g);
boost::add_edge(v_Mona_Simpson, v_Herb_Simpson, g);
boost::add_edge(v_Mona_Simpson, v_Homer_Simpson, g);
boost::add_edge(v_Clancy_Bouvier, v_Marge_Bouvier, g);
boost::add_edge(v_Clancy_Bouvier, v_Patty_Bouvier, g);
boost::add_edge(v_Clancy_Bouvier, v_Selma_Bouvier, g);
boost::add_edge(v_Jacqueline_Bouvier, v_Marge_Bouvier, g);
boost::add_edge(v_Jacqueline_Bouvier, v_Patty_Bouvier, g);
boost::add_edge(v_Jacqueline_Bouvier, v_Selma_Bouvier, g);
boost::add_edge(v_Homer_Simpson, v_Bart_Simpson, g);
boost::add_edge(v_Homer_Simpson, v_Lisa_Simpson, g);
boost::add_edge(v_Homer_Simpson, v_Maggie_Simpson, g);
boost::add_edge(v_Marge_Bouvier, v_Bart_Simpson, g);
boost::add_edge(v_Marge_Bouvier, v_Lisa_Simpson, g);
boost::add_edge(v_Marge_Bouvier, v_Maggie_Simpson, g);
boost::add_edge(v_Selma_Bouvier, v_Ling_Bouvier, g);
typedef std::map<Vertex, size_t>IndexMap;
IndexMap mapIndex;
boost::associative_property_map<IndexMap> propmapIndex(mapIndex);
size_t i=0;
FamilyTree::vertex_iterator vi, vi_end;
for (boost::tie(vi, vi_end) = boost::vertices(g); vi != vi_end; ++vi)
{
boost::put(propmapIndex, *vi, i++);
}
for (boost::tie(vi, vi_end) = boost::vertices(g); vi != vi_end; ++vi)
{
Vertex vParent = *vi;
std::vector<Vertex> vertexDescriptors;
BfsVisitor<FamilyTree> bfsVisitor(vertexDescriptors);
breadth_first_search(g, vParent, visitor(bfsVisitor).vertex_index_map(propmapIndex));
std::cout << "\nDecendants of " << g[vParent].Name << ":\n";
for (auto v : vertexDescriptors)
{
Person p = g[v];
std::cout << p.Name << "\n";
}
}
getchar();
return 0;
}