CODEWITHSUNDEEP
c++fileboostgraph
user6306985
user6306985

Reputation:

How to read a graph from a file using boost?

I want to read a graph from a file using boost. the input file contains the no.of edges followed by the edges in pairs.I want to print the adjacency list.I tried the following code. please help me

    #include <boost/graph/adjacency_list.hpp>
#include <fstream>
#include <boost/graph/graphviz.hpp>
using namespace std;
using namespace boost;
int main(){
    typedef adjacency_list <listS, vecS, directedS> Graph;

    typedef graph_traits<Graph>::vertex_descriptor index_vertex;
    typedef boost::graph_traits <Graph>::edge_iterator edgeIt;
    typedef boost::graph_traits<Graph>::vertex_iterator vertexIt;
    // declare a graph object
    Graph G;
    std::ifstream infile("di.dat");
    index_vertex n_vertices;
    //int n_vertices;
    if(infile >> n_vertices){
        std::cout << n_vertices << endl; // read in number of vertices
    }
    while(infile)
    {
        int f;
        int s;
        infile >> f>> s;
        // std::cout<<first<<second;
        add_edge(f, s, G);     
    }
    infile.close();
    for(pair<vertexIt,vertexIt> vi = boost::vertices(G); vi.first != vi.second; ++vi.first) {
        cout << *vi.first << endl;
    }
    for(pair<edgeIt,edgeIt> ei = boost::edges(G); ei.first != ei.second; ++ei.first) {
        cout << source(*ei.first, G) << " -> " << target(*ei.first, G) << endl;
        //cout << *ei.first << endl;
    }


    ofstream dotfile;
    dotfile.open("test1.dot");
    write_graphviz(dotfile, G);
    system("xdot test1.dot");
    return 0;
}

Input is

14
1 2
2 3
3 4
3 5
4 6
6 7
7 8
7 9
7 10
8 11
9 12

12 13
13 14

Upvotes: 0

Views: 651

Answers (2)

Vtik
Vtik

Reputation: 3140

a basic example to show what's it going wrong is the following :

#include <iostream>

int main(int argc, char**argv)
{
     char j;

     for (int i=0, j='a'; j<'d'; i++, j++)
     {
         std::cout << j << std::endl;
     }

     std::cout << "++++++++++" << std::endl;

         for (j='a'; j<'d';j++)
     {
         std::cout << j << std::endl;
     }

    return 0;
}

output : 

97
98
99
++++++++++
a
b
c

this is a basic example of why this error is thrown. initialising an edge_iterator with an int. revisit your loop as @Marvin said.

Upvotes: 1

Marvin Sielenkemper
Marvin Sielenkemper

Reputation: 820

The int i=0, ei_next = ei; in the for loop defines a new local int variable ei_next since the comma in this case is not the comma-operator but a definition delimiter. And since ei is an edge_iterator it can not be used to initialize the int variable ei_next.

Move the ei_next = ei in the line before the for statement (adding a semicolon) to make it an assignment.

Upvotes: 0

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