Problem in using the Graph object in different function

[Man4ish]

I am creating a graph using boost library, I am making the network using create_Network function()
i am adding the vertices to this graph by creating the object g of class Graph.
I am trying to use this object g in the another function get_neighbours( )
but it is not giving any result.Should I make it global or should use constructor so that values stored in the graph(vertices) object(g), can be used in any function.

#include <boost/config.hpp>
#include <iostream>
#include <vector>
#include <utility>
#include <string>
#include <boost/graph/adjacency_list. hpp>
#include <boost/graph/graph_utility.h pp>
#include <boost/property_map.hp p>
#include "ed.h"
#include "ve.h"
using namespace boost;
using namespace std;

class Molecule
{
typedef adjacency_list< boost::vecS, boost::listS, boost::undirect edS, ve::VertexPrope rties, ed::EdgePropert ies> Graph;
map<int,string> m;

public:
void set_molecule_pr operty(vector<s tring>& s4)
{
for (unsigned int i = 1; i <= s4.size(); i++)
{
m[i]=s4[i-1];
}
}



void create_chemical _Network(vector <int> s1,vector<int> s2,vector<int> s3)
{
const int V = m.size()+1;
Graph g(V);
for (int i = 0; i <V ; i++)
{
if(s3[i]==1){
add_edge(vertex (s1[i], g), vertex(s2[i], g), ed::EdgePropert ies("single bond"), g);
}
if(s3[i]==2){
add_edge(vertex (s1[i], g), vertex(s2[i], g), ed::EdgePropert ies("double bond"), g);
}
if(s3[i]==3){
add_edge(vertex (s1[i], g), vertex(s2[i], g), ed::EdgePropert ies("triple_bon d"), g);
}
}
}

void get_neighbours( )
{
//Graph g(m.size()+1);
Graph g;
property_map<Gr aph, std::size_t ve::VertexPrope rties::*>::type
id = get(&ve::Vertex Properties::ind ex, g);
property_map<Gr aph, std::string ed::EdgePropert ies::*>::type
name = get(&ed::EdgePr operties::name, g);
boost::graph_tr aits<Graph>::ve rtex_iterator vi, viend;
int vnum = 0;
for (boost::tie(vi, viend) = vertices(g); vi != viend; ++vi)
id[*vi] = vnum++;
graph_traits<Gr aph>::vertex_it erator i, end;
graph_traits<Gr aph>::out_edge_ iterator ei, edge_end;
for (boost::tie(i,e nd) = vertices(g); i != end; ++i)
{
if(id[*i]!=0)
{
cout << id[*i]<<"("<<m[id[*i]]<<")" << " ";
for (boost::tie(ei, edge_end) = out_edges(*i, g); ei != edge_end; ++ei)
cout << " --" << name[*ei] << "--> " << m[id[target(*ei, g)]] << " ";
cout << endl;
}
}
print_edges(g, id);
cout<<endl;
print_vertices( g,id);
}
};

int main(int,char* [])
{
using namespace boost;
Molecule mol;
int s11[]={1,1,2,2,3,3,4 ,4,5,5,6,6,6,7, 7,7,8,8,8,8,9,9 ,10,10,11,11,12 ,12,13,14,17,19 ,19,19,20,20,20 ,21,21,21};
int s12[]={13,19,14,20,1 5,21,16,18,17,1 8,16,27,28,18,3 8,39,9,10,22,23 ,11,12,16,17,14 ,24,13,25,15,15 ,26,29,30,31,32 ,33,34,35,36,37 };
int s13[]={1,1,1,1,1,1,2 ,1,1,2,1,1,1,1, 1,1,1,1,1,1,2,1 ,1,2,1,1,2,1,1, 2,1,1,1,1,1,1,1 ,1,1,1};
string s14[]={"O","O","O"," N","N","N","N", "C","C","C","C" ,"C","C","C","C ","C","C","C"," C","C","C","H", "H","H","H","H" ,"H","H","H","H ","H","H","H"," H","H","H","H", "H","H"};
vector <string> s4;
vector <int> s1,s2,s3;

for (unsigned int i = 0; i < sizeof(s11)/sizeof(string); i++)
{
s1.push_back(s1 1[i]);
s2.push_back(s1 2[i]);
s3.push_back(s1 3[i]);
}


for (unsigned int i = 0; i < sizeof(s14)/sizeof(string); i++)
{
s4.push_back(s1 4[i]);
}
mol.set_molecul e_property(s4);
mol.create_chem ical_Network(s1 ,s2,s3);
mol.get_neighbo urs();
return 0;
}

Please Help me out of this pblm.I will be really thankful to you.

[weaknessforcats]

Your Graph objects are local to the funciton. Local variables are destroyed when the function ends.

The Graph object g in get_neighbours( ) is not the one created in create_chemical _Network().

You need to create your Graph object on the heap and then pass a pointer to it to your various functions.

Also, get_neighbours( ) has no arguments and returns a void. That means your entire application is inside this thing, in which case having the funciton at all is pointless. Or you are using global variables which are a disaster waiting to happen.

If you are using global variables, the you should read the Case Against Global Variables in the C/C++ HowTos forum.