std::next in C++

Last Updated : 02 Aug, 2017

std::next returns an iterator pointing to the element after being advanced by certain no. of positions. It is defined inside the header file .

It does not modify its arguments and returns a copy of the argument advanced by the specified amount. If it is a random-access iterator, the function uses just once operator + or operator – for advancing. Otherwise, the function uses repeatedly the increase or decrease operator (operator ++ or operator –) on the copied iterator until n elements have been advanced.

Syntax:

  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.

Output:

  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.

   // 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.