Editing Smart pointer (section)

== unique_ptr ==
[[C++11]] introduces {{code|std::unique_ptr}}, defined in the header {{code|<memory>}}.<ref name="ISO14882_2011"/>

A {{code|unique_ptr}} is a container for a raw pointer, which the <code>unique_ptr</code> is said to own. A <code>unique_ptr</code> explicitly prevents copying of its contained pointer (as would happen with normal assignment), but the {{code|std::move}} function can be used to transfer ownership of the contained pointer to another {{code|unique_ptr}}. A <code>unique_ptr</code> cannot be copied because its copy constructor and assignment operators are explicitly deleted.

<syntaxhighlight lang="cpp">
std::unique_ptr<int> p1(new int(5));
std::unique_ptr<int> p2 = p1;  // Compile error.
std::unique_ptr<int> p3 = std::move(p1);  // Transfers ownership. p3 now owns the memory and p1 is set to nullptr.

p3.reset();  // Deletes the memory.
p1.reset();  // Does nothing.
</syntaxhighlight>

<code>std::[[auto_ptr]]</code> is [[Deprecation|deprecated]] under C++11 and completely removed from [[C++17]]. The copy constructor and assignment operators of {{code|auto_ptr}} do not actually copy the stored pointer. Instead, they [[Auto ptr#Semantics|transfer it]], leaving the prior {{code|auto_ptr}} object empty. This was one way to implement strict ownership, so that only one {{code|auto_ptr}} object can own the pointer at any given time. This means that {{code|auto_ptr}} should not be used where copy semantics are needed.<ref name="CERT"/>{{citation needed|date=September 2016}} Since {{code|auto_ptr}} already existed with its copy semantics, it could not be upgraded to be a move-only pointer without breaking [[backward compatibility]] with existing code.