std::next in C++ (original) (raw)

Last Updated : 2 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.

CPP `

// C++ program to demonstrate std::next #include #include #include #include using namespace std; int main() { // Declaring first container deque 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. CPP `
  // C++ program to demonstrate std::next

#include
#include
#include
#include
using namespace std;
int main()
{
// Declaring first container
list v1 = { 1, 2, 3, 7, 8, 9 };
// Declaring second container
list v2 = { 4, 5, 6 };
list::iterator i1;
i1 = v1.begin();
// i1 points to 1 in v1
list::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.