函数将迭代器返回到向量

Question

what is the best way of returning an iterator for the below code?In the below code it is not giving correct output for this line

cout<<*p<<endl;

---

#include<iostream>
#include<vector>
using namespace std;
vector <int> :: iterator int_begin(vector <int> V);
int main()
{
  vector <int> V;
  V.push_back(3);
  V.push_back(1);
  vector <int> :: iterator p=int_begin(V);
  cout<<*p<<endl;
  return 0;
}
vector <int> :: iterator int_begin(vector <int> V)
{
  cout<<*V.begin()<<endl;
  return V.begin();
}

Answer 1

You are passing the object by value to int_begin() . What you get back is an iterator to a std::vector that does not live past the function call. Hence, in the calling function, the iterator is invalid.

Pass the object by reference.

vector <int> :: iterator int_begin(vector <int>& V) // Passed by reference
{
  cout<<*V.begin()<<endl;
  return V.begin();
}