std::next in C++

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.

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Article Tags :

• C++
• Misc
• cpp-iterator
• STL

Practice Tags :

• CPP
• Misc
• STL