test/std/iterators/predef.iterators/reverse.iterators/reverse.iter.ops/reverse.iter.op+/difference_type.pass.cpp

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// <iterator>

// reverse_iterator

// requires RandomAccessIterator<Iter>
//   constexpr reverse_iterator operator+(difference_type n) const;
//
// constexpr in C++17

#include <iterator>
#include <cassert>

#include "test_macros.h"
#include "test_iterators.h"

template <class It>
void
test(It i, typename std::iterator_traits<It>::difference_type n, It x)
{
    const std::reverse_iterator<It> r(i);
    std::reverse_iterator<It> rr = r + n;
    assert(rr.base() == x);
}

int main(int, char**)
{
    const char* s = "1234567890";
    test(random_access_iterator<const char*>(s+5), 5, random_access_iterator<const char*>(s));
    test(s+5, 5, s);

#if TEST_STD_VER > 14
    {
        constexpr const char *p = "123456789";
        typedef std::reverse_iterator<const char *> RI;
        constexpr RI it1 = std::make_reverse_iterator(p);
        constexpr RI it2 = std::make_reverse_iterator(p + 5);
        constexpr RI it3 = it2 + 5;
        static_assert(it1 != it2, "");
        static_assert(it1 == it3, "");
        static_assert(it2 != it3, "");
    }
#endif

  return 0;
}