Defined in header <iterator> | ||
|---|---|---|
template< class InputIt >
typename std::iterator_traits<InputIt>::difference_type
distance( InputIt first, InputIt last );
| (until C++17) | |
template< class InputIt >
constexpr typename std::iterator_traits<InputIt>::difference_type
distance( InputIt first, InputIt last );
| (since C++17) |
Returns the number of hops from first to last.
| The behavior is undefined if | (until C++11) | |
| If | (since C++11) | |
| first | - | iterator pointing to the first element |
| last | - | iterator pointing to the end of the range |
| Type requirements | ||
-InputIt must meet the requirements of InputIterator. The operation is more efficient if InputIt additionally meets the requirements of RandomAccessIterator |
||
The number of increments needed to go from first to last. The value may be negative if random-access iterators are used and first is reachable from last (since C++11).
Linear.
However, if InputIt additionally meets the requirements of RandomAccessIterator, complexity is constant.
#include <iostream>
#include <iterator>
#include <vector>
int main()
{
std::vector<int> v{ 3, 1, 4 };
std::cout << "distance(first, last) = "
<< std::distance(v.begin(), v.end()) << '\n'
<< "distance(last, first) = "
<< std::distance(v.end(), v.begin()) << '\n';
}Output:
distance(first, last) = 3 distance(last, first) = -3
| advances an iterator by given distance (function) |
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