1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9// <iterator>
10
11// template <InputIterator Iter>
12// Iter prev(Iter x, Iter::difference_type n = 1); // constexpr in C++17
13
14#include <iterator>
15#include <cassert>
16#include <type_traits>
17
18#include "test_macros.h"
19#include "test_iterators.h"
20
21template <class It>
22TEST_CONSTEXPR_CXX17 void
23check_prev_n(It it, typename std::iterator_traits<It>::difference_type n, It result)
24{
25 static_assert(std::is_same<decltype(std::prev(it, n)), It>::value, "");
26 assert(std::prev(it, n) == result);
27
28 It (*prev_ptr)(It, typename std::iterator_traits<It>::difference_type) = std::prev;
29 assert(prev_ptr(it, n) == result);
30}
31
32template <class It>
33TEST_CONSTEXPR_CXX17 void
34check_prev_1(It it, It result)
35{
36 static_assert(std::is_same<decltype(std::prev(it)), It>::value, "");
37 assert(std::prev(it) == result);
38}
39
40TEST_CONSTEXPR_CXX17 bool tests()
41{
42 const char* s = "1234567890";
43 check_prev_n(forward_iterator <const char*>(s), -10, forward_iterator <const char*>(s+10));
44 check_prev_n(bidirectional_iterator<const char*>(s+10), 10, bidirectional_iterator<const char*>(s));
45 check_prev_n(bidirectional_iterator<const char*>(s), -10, bidirectional_iterator<const char*>(s+10));
46 check_prev_n(random_access_iterator<const char*>(s+10), 10, random_access_iterator<const char*>(s));
47 check_prev_n(random_access_iterator<const char*>(s), -10, random_access_iterator<const char*>(s+10));
48 check_prev_n(s+10, 10, s);
49
50 check_prev_1(bidirectional_iterator<const char*>(s+1), bidirectional_iterator<const char*>(s));
51 check_prev_1(random_access_iterator<const char*>(s+1), random_access_iterator<const char*>(s));
52 check_prev_1(s+1, s);
53
54 return true;
55}
56
57int main(int, char**)
58{
59 tests();
60#if TEST_STD_VER >= 17
61 static_assert(tests(), "");
62#endif
63 return 0;
64}
65

source code of libcxx/test/std/iterators/iterator.primitives/iterator.operations/prev.pass.cpp