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.
// 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;
} |
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.