65 lines · 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-exception6//7//===----------------------------------------------------------------------===//8 9// <iterator>10 11// template <InputIterator Iter>12// Iter prev(Iter x, Iter::difference_type n = 1); // constexpr in C++1713 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 void23check_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 void34check_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 >= 1761 static_assert(tests(), "");62#endif63 return 0;64}65