Difference between revisions of "cpp/iterator/next"

Revision as of 15:18, 26 October 2022

Return the nth successor (or -nth predecessor if n is negative) of iterator it.

Parameters

Return value

The nth successor (or -nth predecessor if n is negative) of iterator it.

Complexity

Linear.

However, if InputIt additionally meets the requirements of LegacyRandomAccessIterator, complexity is constant.

Possible implementation

template<class InputIt>
constexpr // since C++17
InputIt next(InputIt it,
             typename std::iterator_traits<InputIt>::difference_type n = 1)
{
    std::advance(it, n);
    return it;
}

Notes

Although the expression ++c.begin() often compiles, it is not guaranteed to do so: c.begin() is an rvalue expression, and there is no LegacyInputIterator requirement that specifies that increment of an rvalue is guaranteed to work. In particular, when iterators are implemented as pointers or its operator++ is lvalue-ref-qualified, ++c.begin() does not compile, while std::next(c.begin()) does.

Example

#include <iostream>
#include <iterator>
#include <vector>
 
int main() 
{
    std::vector<int> v{ 4, 5, 6 };
 
    auto it = v.begin();
    auto nx = std::next(it, 2);
    std::cout << *it << ' ' << *nx << '\n';
 
    it = v.end();
    nx = std::next(it, -2);
    std::cout << ' ' << *nx << '\n';
}

4 6
 5

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also