#include <iterator>

template <class Bi>
Bi prev(Bi iter, typename iterator_traits<Bi>::difference_type n = 1)

Liefert einen Iterator auf das n-te Element vor *iter eines Containerbereichs.

Rückgabewert:

  auto result = iter;
  advance(result, -n);
  return result;

advance(), distance(), next().

prev.cpp

#include <iterator>
#include <vector>
#include <iostream>
 
int main()
{
  std::vector<double> v = { 1, 2, 3, 4, 5 };
  auto m = begin(v) + distance(begin(v), end(v)) / 2; 
  std::cout << *prev(m) << '\n';
  std::cout << *m << '\n';
  std::cout << *next(m) << '\n';
}