https://stackoverflow.com/q/75401520/16582

main.cpp

#include <string>
#include <fstream>
#include <sstream>
#include <iostream>
#include <vector>

/// @brief A graph edge
class edge
{
public:
    std::string v1;
    std::string v2;
    std::string attr;

    edge(
        const std::string &s1,
        const std::string &s2,
        const std::string &sattr)
        : v1(s1),
          v2(s2),
          attr(sattr)
    {
    }
    void display()
    {
        std::cout << v1 << " | "<< v2 <<" | "<< attr << "\n";
    }
};

/// @brief define graph type

typedef std::vector<edge> graph_t;

/// @brief split line into space delimited tokens
/// @param line 
/// @return vector of tokens

std::vector<std::string> tokenize(const std::string &line)
{
    std::vector<std::string> ret;
    std::stringstream sst(line);
    std::string a;
    while (getline(sst, a, ' '))
        ret.push_back(a);
    return ret;
}

/// @brief Output text listing graph edges
/// @param[in] g 

void display(graph_t& g)
{
    std::cout << "v1 | v2 | atribute\n|---|---|---|\n";
    for( edge& e : g )
    {
        e.display();
    }
}
/// @brief read graph from input file
/// @param[in/out] g graph to add edges to
/// @param fname input file path

void read(
    graph_t& g,
    const std::string &fname)
{
    std::ifstream ifs(fname);
    if (!ifs.is_open())
        throw std::runtime_error("no input file");
    std::string line;
    while (getline(ifs, line))
    {
        auto vtoken = tokenize(line);
        g.push_back( edge( vtoken[0],vtoken[1],"bf"));
        for( int k = 2; k<vtoken.size(); k++ )
            g.push_back( edge( vtoken[0],vtoken[k],"ff"));
    }
}

main()
{
    // construct graph
    graph_t g;

    // read edges from file
    read(g,"input.txt");

    // display edges
    display(g);
    return 0;
}