Smart Pointers

Smart pointer types:

• Usually a class template.

• Behaves syntactically in a similar way to pointers.

• Has the special member functions, for construction, destruction, moving and copying, defined to maintain certain invariants.

• Roughly they make sure we don’t run into problem with: Memory leaks, use-after-freeing, heap corruption via pointer arithmetic (we free the wrong location).

• They automatically delete the object to which theypoint.Standard smart pointers ...

There are two standard smart pointer types from C++11, defined in the memory header. The first, std::unique_ptr<T>, defines a pointer that owns the thing pointed to.

• So if you call the destructor for the unique_ptr, the thing pointed too will be destroyed too.

• As would seem sensible, at any time there can only be a single unique_ptr to a given object.

• There is a version std::unique_ptr<T,D> with D being the defined deleter, defaulting to std::default_delete<T>, which calls operator delete.

The RAII idea:

Whenever we allocate a resource, we initialize a unique_ptr to manage it. Avoid using new directly...The second is for managing situations where we want multiple references to the same object...

std::shared_ptr<T>

They can be set up using statements like:

shared_ptr<string> p1;
shared_ptr<list<int>> p2;

The shared_ptr records how many references there are to an object and destroys the object iff the last reference to the object is being destroyed.

• And in doing so tidies up the memory.