C++：distance()

function template

std::distance
template
typename iterator_traits::difference_type
distance (InputIterator first, InputIterator last);
Return distance between iterators
Calculates the number of elements between first and last.

If it is a random-access iterator, the function uses operator- to calculate this. Otherwise, the function uses the increase operator (operator++) repeatedly.

Parameters
first: Iterator pointing to the initial element.
last: Iterator pointing to the final element. This must be reachable from first.
InputIterator shall be at least an input iterator.

Return value
The number of elements between first and last.

Example
// advance example

#include <iostream>     // std::cout#include <iterator>     // std::distance#include <list>         // std::listint main () {  std::list<int> mylist;  for (int i=0; i<10; i++) mylist.push_back (i*10);  std::list<int>::iterator first = mylist.begin();  std::list<int>::iterator last = mylist.end();  std::cout << "The distance is: " << std::distance(first,last) << '\n';  return 0;}

Output:

The distance is: 10