Creating graph in loop from Boost library c++ - c++

Question

I am trying to convert myself from R to C++ and am struggling with a particular graph problem. I have a String Matrix called "Gra" as below.
int main(){
string Gra[4][5] = {{"V0", "V1", "V2", "V3", "V4"},
{"V5", "V6", "NA", "NA", "V7"},
{"V8", "V9", "NA", "NA", "V10"},
{"V11", "V12", "V13", "V14", "V15"}};
Where "V0" represents a node and "NA" is not. This matrix came from the matrix called "base"
int base[4][5] = {{1, 1, 1, 1, 1},
{1, 1, 0, 0, 1},
{1, 1, 0, 0, 1},
{1, 1, 1, 1, 1}};
typedef float Weight;
typedef boost::property<boost::edge_weight_t, Weight> WeightProperty;
typedef boost::property<boost::vertex_name_t, std::string> NameProperty;
typedef boost::adjacency_list < boost::listS, boost::vecS, boost::directedS,
NameProperty, WeightProperty > Graph;
typedef boost::graph_traits < Graph >::vertex_descriptor Vertex;
typedef boost::property_map < Graph, boost::vertex_index_t >::type IndexMap;
typedef boost::property_map < Graph, boost::vertex_name_t >::type NameMap;
typedef boost::iterator_property_map < Vertex*, IndexMap, Vertex, Vertex& > PredecessorMap;
typedef boost::iterator_property_map < Weight*, IndexMap, Weight, Weight& > DistanceMap;
Graph g;
Where the problem is, trying to describe the graph in a loop. I would like to declare the nodes as
Vertex V0 = boost::add_vertex(std::string("V0"), g); // Struggling to implement this in a loop
Vertex V1 = boost::add_vertex(std::string("V1"), g);
Vertex V2 = boost::add_vertex(std::string("V2"), g);
Vertex V3 = boost::add_vertex(std::string("V3"), g);
Vertex V4 = boost::add_vertex(std::string("V4"), g);
Vertex V5 = boost::add_vertex(std::string("V5"), g);
Vertex V6 = boost::add_vertex(std::string("V6"), g);
Vertex V7 = boost::add_vertex(std::string("V7"), g);
Vertex V8 = boost::add_vertex(std::string("V8"), g);
Vertex V9 = boost::add_vertex(std::string("V9"), g);
Vertex V10 = boost::add_vertex(std::string("V10"), g);
Vertex V11 = boost::add_vertex(std::string("V11"), g);
Vertex V12 = boost::add_vertex(std::string("V12"), g);
Vertex V13 = boost::add_vertex(std::string("V13"), g);
Vertex V14 = boost::add_vertex(std::string("V14"), g);
Vertex V15 = boost::add_vertex(std::string("V15"), g);
How I have tried to replicate this is through a loop like this.
for ( int i=0; i < 4; i++) // So this will run along all elements of our base vector
{
for ( int j=0; j < 5; j++) // Length is the number of elements in our array
{
if( !(Gra[i][j] == "NA")) // Whilst going along each element inspecting whether it is a true node
{
Vertex Gra[i][j] = boost::add_vertex(std::Gra[i][j], g); // This is where the problem is
}
}
}
So the problem comes from using a string to define this object of class Vertex. Could any body help me? I'm pretty sure this is a naming convention issue that I'm struggling with. If this is solved then I can solve the rest of my problems in terms of creating the edges which I also have the same problem of trying to call an object of class "vertex" using a string.
Thanks in advance Cyrill

Answer 1

The expression !Gra[i][j] == "NA" will not do what you expect it to. It will first check that Gra[i][j] is not "false" and then compare the boolean result with the string "NA".
Instead either use parentheses around the equality check, or do a not-equal check. So either
!(Gra[i][j] == "NA")
or
Gra[i][j] != "NA"
There's also the problem that you declare a local array-of-arrays variable Gra inside the inner loop, which will cause clashes with your outer Gra variable. I guess that's why you use std::Gra there, but Gra is not declared in the standard namespace. Neither can you use ::Gra because Gra is not declared in the global namespace either.
Instead of declaring a new variable inside the inner loop, declare an array Vertexes outside the loop:
Vertex Vertexes[4][5];
Then use that variable to store the result of boost::add_vertex.