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

//===----------------------------------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

// <iterator>

// template <BidirectionalIterator Iter>
//   Iter prev(Iter x, Iter::difference_type n = 1);

#include <iterator>
#include <cassert>

#include "test_iterators.h"

template <class It>
void
test(It i, typename std::iterator_traits<It>::difference_type n, It x)
{
    assert(std::prev(i, n) == x);
}

template <class It>
void
test(It i, It x)
{
    assert(std::prev(i) == x);
}

#if TEST_STD_VER > 14
template <class It>
constexpr bool
constexpr_test(It i, typename std::iterator_traits<It>::difference_type n, It x)
{
    return std::prev(i, n) == x;
}

template <class It>
constexpr bool
constexpr_test(It i, It x)
{
    return std::prev(i) == x;
}
#endif

int main()
{
    {
    const char* s = "1234567890";
    test(bidirectional_iterator<const char*>(s+10), 10, bidirectional_iterator<const char*>(s));
    test(random_access_iterator<const char*>(s+10), 10, random_access_iterator<const char*>(s));
    test(s+10, 10, s);

    test(bidirectional_iterator<const char*>(s+1), bidirectional_iterator<const char*>(s));
    test(random_access_iterator<const char*>(s+1), random_access_iterator<const char*>(s));
    test(s+1, s);
    }
#if TEST_STD_VER > 14
    {
    constexpr const char* s = "1234567890";
    static_assert( constexpr_test(bidirectional_iterator<const char*>(s+10), 10, bidirectional_iterator<const char*>(s)), "" );
    static_assert( constexpr_test(random_access_iterator<const char*>(s+10), 10, random_access_iterator<const char*>(s)), "" );
    static_assert( constexpr_test(s+10, 10, s), "" );

    static_assert( constexpr_test(bidirectional_iterator<const char*>(s+1), bidirectional_iterator<const char*>(s)), "" );
    static_assert( constexpr_test(random_access_iterator<const char*>(s+1), random_access_iterator<const char*>(s)), "" );
    static_assert( constexpr_test(s+1, s), "" );
    }
#endif

}