包含引用的对象的向量

Question

Edge 

{
   Vertex& v1;
   Vertex& v2;
   float cost;
public :
   Edge(Vertex& v_1, Vertex& v_2) :
      v1(v_1), v2(v_2)
   {
   }
   // other getter and setter functions 
};

How do I create a vector allEdges ? I know I'll have to create a default constructors and assignment operators supported by vector but I can already see this is going to create issues because of non-existence of default constructors.

I have created a default constructor just to get by with the std::vector shouting at me but doesn't seem like the right thing to do.

Answer 1

Using references as member variable is quite restrictive since they have to be initialized in the initializer list of the constructor.

However, having a vector of objects that in turn have references as member variables is completely allowable, as can be seen in the example below:

#include <vector>
#include <iostream>

struct Vertex { 
  std::size_t id;
  Vertex(std::size_t const _id) : id(_id) {}
};

class Edge {
   Vertex& v1;
   Vertex& v2;
   double  cost;
public :
   Edge(Vertex& v_1, Vertex& v_2, double const _c) : v1(v_1), v2(v_2), cost(_c) {}
   Vertex& getv1() const { return v1; }
   Vertex& getv2() const { return v2; }
};

int main() {
    Vertex v1(1), v2(2);
    std::vector<Edge> alledges;
    alledges.push_back(Edge(v1, v2, 1.0));
    for(auto i : alledges) std::cout << i.getv1().id << "->" << i.getv2().id << std::endl;

    return 0;
}

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