具有重叠范围的 std::unique_copy

Question

template< class InputIt, class OutputIt >
OutputIt unique_copy( InputIt first, InputIt last,
                      OutputIt d_first );

Is it valid to use std::unique_copy if input range and output range overlap? Consider the following two example cases

auto d_last = std::unique_copy(first, last, d_first);

1. d_first <= first <= d_last <= last
2. first <= d_first <= last <= d_last

Answer 1

The preconditions for std::unique_copy are described in [algorithms#alg.unique-8] :

 template<class InputIterator, class OutputIterator> constexpr OutputIterator unique_copy(InputIterator first, InputIterator last, OutputIterator result);

Preconditions :

• The ranges [first, last) and [result, result+(last-first)) do not overlap.

So this is undefined behavior.