Question

What is the most elegant way to perform a loop and stop after the second to last element (in C++11)?

Note: I mean for bidirectional iterators; random access iterators are a trivial special case, of course, because they have + and - operators.

std::list<double> x{1,2,3,4,5,6};

for (auto iter = x.begin(); iter != x.end(); ++iter) {
  auto iter2 = iter;
  ++iter2;
  if (iter2 == x.end()) break;
  std::cout << *iter << std::endl;
}

Answer 1

Use the std::prev function:

std::list<double> x{1,2,3,4,5,6};

for (auto iter = x.begin(); iter != std::prev(x.end()); ++iter) {
  std::cout << *iter << std::endl;
}