Why does unique_ptr have an overload for auto_ptr?

Question

I got a compiler error and noticed something interesting. For some reason unique_ptr has an overload for auto_ptr, but I thought auto_ptr was deprecated:

/usr/local/include/c++/4.9.0/bits/unique_ptr.h:228:2: 
note:template<class _Up, class> 
std::unique_ptr<_Tp, _Dp>::unique_ptr(std::auto_ptr<_Up>&&)
  unique_ptr(auto_ptr<_Up>&& __u) noexcept;

/usr/local/include/c++/4.9.0/bits/unique_ptr.h:228:2: 
note: template argument deduction/substitution failed:
main.cpp:41:67: note:  mismatched types 'std::auto_ptr<T>' and 'char*'

Is this because of backwards compatibility with code that used auto_ptr?

Answer 1

Yes, it's for interop with auto_ptr, and deprecated means (according to the standard)

Normative for the current edition of the Standard, but not guaranteed to be part of the Standard in future revisions.