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

   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 }