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);
13 
14 #include <iterator>
15 #include <cassert>
16 
17 #include "test_macros.h"
18 #include "test_iterators.h"
19 
20 template <class It>
21 void
22 test(It i, typename std::iterator_traits<It>::difference_type n, It x)
23 {
24     assert(std::prev(i, n) == x);
25 
26     It (*prev)(It, typename std::iterator_traits<It>::difference_type) = std::prev;
27     assert(prev(i, n) == x);
28 }
29 
30 template <class It>
31 void
32 test(It i, It x)
33 {
34     assert(std::prev(i) == x);
35 }
36 
37 #if TEST_STD_VER > 14
38 template <class It>
39 constexpr bool
40 constexpr_test(It i, typename std::iterator_traits<It>::difference_type n, It x)
41 {
42     return std::prev(i, n) == x;
43 }
44 
45 template <class It>
46 constexpr bool
47 constexpr_test(It i, It x)
48 {
49     return std::prev(i) == x;
50 }
51 #endif
52 
53 int main(int, char**)
54 {
55     {
56     const char* s = "1234567890";
57     test(forward_iterator      <const char*>(s),    -10, forward_iterator      <const char*>(s+10));
58     test(bidirectional_iterator<const char*>(s+10),  10, bidirectional_iterator<const char*>(s));
59     test(bidirectional_iterator<const char*>(s),    -10, bidirectional_iterator<const char*>(s+10));
60     test(random_access_iterator<const char*>(s+10),  10, random_access_iterator<const char*>(s));
61     test(random_access_iterator<const char*>(s),    -10, random_access_iterator<const char*>(s+10));
62     test(s+10, 10, s);
63 
64     test(bidirectional_iterator<const char*>(s+1), bidirectional_iterator<const char*>(s));
65     test(random_access_iterator<const char*>(s+1), random_access_iterator<const char*>(s));
66     test(s+1, s);
67     }
68 #if TEST_STD_VER > 14
69     {
70     constexpr const char* s = "1234567890";
71     static_assert( constexpr_test(forward_iterator      <const char*>(s),    -10, forward_iterator      <const char*>(s+10)), "" );
72     static_assert( constexpr_test(bidirectional_iterator<const char*>(s+10),  10, bidirectional_iterator<const char*>(s)), "" );
73     static_assert( constexpr_test(forward_iterator      <const char*>(s),    -10, forward_iterator      <const char*>(s+10)), "" );
74     static_assert( constexpr_test(random_access_iterator<const char*>(s+10),  10, random_access_iterator<const char*>(s)), "" );
75     static_assert( constexpr_test(forward_iterator      <const char*>(s),    -10, forward_iterator      <const char*>(s+10)), "" );
76     static_assert( constexpr_test(s+10, 10, s), "" );
77 
78     static_assert( constexpr_test(bidirectional_iterator<const char*>(s+1), bidirectional_iterator<const char*>(s)), "" );
79     static_assert( constexpr_test(random_access_iterator<const char*>(s+1), random_access_iterator<const char*>(s)), "" );
80     static_assert( constexpr_test(s+1, s), "" );
81     }
82 #endif
83 
84 
85   return 0;
86 }
87