std::next in C++

 ForwardIterator next (ForwardIterator it, typename iterator_traits::difference_type n = 1); it: Iterator to the base position. difference_type: It is the numerical type that represents distances between iterators of the ForwardIterator type. n: Total no. of positions by which the iterator has to be advanced. In the syntax, n is assigned a default value 1 so it will atleast advance by 1 position. Returns: It returns an iterator to the element n positions away from it. 

// C++ program to demonstrate std::next #include <iostream> #include <iterator> #include <deque> #include <algorithm> using namespace std; int main() {  // Declaring first container  deque<int> v1 = { 1, 2, 3, 4, 5, 6, 7 };  // Declaring another container  deque<int> v2 = { 8, 9, 10 };  // Declaring an iterator  deque<int>::iterator i1;  // i1 points to 1  i1 = v1.begin();  // Declaring another iterator to store return  // value and using std::next  deque<int>::iterator i2;  i2 = std::next(i1, 4);  // Using std::copy  std::copy(i1, i2, std::back_inserter(v2));  // Remember, i1 stills points to 1  // and i2 points to 5  // v2 now contains 8 9 10 1 2 3 4  // Displaying v1 and v2  cout << "v1 = ";  int i;  for (i = 0; i < 7; ++i) {  cout << v1[i] << " ";  }  cout << "\nv2 = ";  for (i = 0; i < 7; ++i) {  cout << v2[i] << " ";  }  return 0; } 

 v1 = 1 2 3 4 5 6 7 v2 = 8 9 10 1 2 3 4 

How can it be helpful ?

• Advancing iterator in Lists: Since, lists support bidirectional iterators, which can be incremented only by using ++ and - - operator. So, if we want to advance the iterator by more than one position, then using std::next can be extremely useful. CPP

  // C++ program to demonstrate std::next #include <iostream> #include <iterator> #include <list> #include <algorithm> using namespace std; int main() {  // Declaring first container  list<int> v1 = { 1, 2, 3, 7, 8, 9 };  // Declaring second container  list<int> v2 = { 4, 5, 6 };  list<int>::iterator i1;  i1 = v1.begin();  // i1 points to 1 in v1  list<int>::iterator i2;  // i2 = v1.begin() + 3;  // This cannot be used with lists  // so use std::next for this  i2 = std::next(i1, 3);  // Using std::copy  std::copy(i1, i2, std::back_inserter(v2));  // v2 now contains 4 5 6 1 2 3  // Displaying v1 and v2  cout << "v1 = ";  int i;  for (i1 = v1.begin(); i1 != v1.end(); ++i1) {  cout << *i1 << " ";  }  cout << "\nv2 = ";  for (i1 = v2.begin(); i1 != v2.end(); ++i1) {  cout << *i1 << " ";  }  return 0; } 

  Output:

   v1 = 1 2 3 7 8 9 v2 = 4 5 6 1 2 3 

  Explanation: Here, just look how if we want copy only a selected portion of the list, then we can make use of std::next, as otherwise we cannot use any +=, -= operators with bidirectional iterators supported by lists. So, we used std::next and directly advanced the iterator by three positions.