Can a unique_ptr take a nullptr value?

Question

Is this code fragment valid? :

unique_ptr<A> p(new A());
p = nullptr;

That is, can I assign nullptr to a unique_ptr ? or it will fail?

I tried this with the g++ compiler and it worked, but what about other compilers?

Answer 1

It will work.

From Paragraphs 20.7.1.2.3/8-9 of the C++11 Standard about the unique_ptr<> class template:

unique_ptr& operator=(nullptr_t) noexcept;

Effects: reset().

Postcondition: get() == nullptr

This means that the definition of class template unique_ptr<> includes an overload of operator = that accepts a value of type nullptr_t (such as nullptr) as its right hand side; the paragraph also specifies that assigning nullptr to a unique_ptr is equivalent to resetting the unique_ptr.

Thus, after this assignment, your A object will be destroyed.