overloading ostream for any function that returns a vector

Hi assume that I have class A :

using namespace std;
template <class T>
class A{
private:
 vector<T> my_V;
public:
 // assume initializations etc are done
 inline vector<T> get_v()
 {
   return my_v;
 }
};

and some where else I 开发者_如何学Gohave overloaded ostream of std::vector

template <class T>
ostream & operator<<(ostream& out, vector<T> &vec)
{
    CUI size=vec.size();
    for (int i = 0; i < size; i++)
        out << vec.at(i) << " ";
    if(size>0)out << endl;
    return out;
}

when I try to

A<int> obj;
cout<<obj.get_v; // gives soo many errors

but when I do

A<int> obj;
vector<int> v= obj.get_v;
cout<<v; // it works fine

I understand something wrong with the ostream overloading or I might need other overloading technique can someone please help me with that ? Thanks in advance

Your operator<< overload takes a non-const reference. Your A<T>::get_v() function returns a std::vector<T> by value; this returned object is a temporary. A non-const reference cannot bind to a temporary object.

Your overload needs to take a const reference (const std::vector<T>&).