std::iterator_traits

Header: <iterator>

std::iterator_traits is the type trait class that provides uniform interface to the properties of LegacyIterator types. This makes it possible to implement algorithms only in terms of iterators.

# Declarations

template< class Iter >
struct iterator_traits;

template< class T >
struct iterator_traits<T*>;

template< class T >
struct iterator_traits<const T*>;

(removed in C++20)

# Example

#include <iostream>
#include <iterator>
#include <list>
#include <vector>
 
template<class BidirIt>
void my_reverse(BidirIt first, BidirIt last)
{
    typename std::iterator_traits<BidirIt>::difference_type n = std::distance(first, last);
    for (--n; n > 0; n -= 2)
    {
        typename std::iterator_traits<BidirIt>::value_type tmp = *first;
        *first++ = *--last;
        *last = tmp;
    }
}
 
int main()
{
    std::vector<int> v{1, 2, 3, 4, 5};
    my_reverse(v.begin(), v.end());
    for (int n : v)
        std::cout << n << ' ';
    std::cout << '\n';
 
    std::list<int> l{1, 2, 3, 4, 5};
    my_reverse(l.begin(), l.end());
    for (int n : l)
        std::cout << n << ' ';
    std::cout << '\n';
 
    int a[]{1, 2, 3, 4, 5};
    my_reverse(a, a + std::size(a));
    for (int n : a)
        std::cout << n << ' ';
    std::cout << '\n';
 
//  std::istreambuf_iterator<char> i1(std::cin), i2;
//  my_reverse(i1, i2); // compilation error: i1, i2 are input iterators
}

# See also