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 
21 template <class It>
22 TEST_CONSTEXPR_CXX17 void
23 check_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 
32 template <class It>
33 TEST_CONSTEXPR_CXX17 void
34 check_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 
40 TEST_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 
57 int main(int, char**)
58 {
59     tests();
60 #if TEST_STD_VER >= 17
61     static_assert(tests(), "");
62 #endif
63     return 0;
64 }
65