Shared Pointers

Next, we have the shared pointer. It follows the principle of keeping a reference count to maintain the count of its copies. The lesson below elaborates further.

std::shared_ptr shares the ownership of the resource. They have two handles. One for the resource and one for the reference counter. By copying a std::shared_ptr, the reference count is increased by one. It is decreased by one if the std::shared_ptr goes out of scope. If the reference counter becomes the value 0 and therefore there is no std::shared_ptr referencing the resource, the C++ runtime automatically releases the resource. The release of the resource takes place at exactly the time at which the last std::shared_ptr goes out of scope. The C++ runtime guarantees that the call of the reference counter is an atomic operation. Because of this management, std::shared_ptr uses more time and memory than a raw pointer or std::unique_ptr.

In the following table are the methods of std::shared_ptr:

Name Description
get Returns a pointer to the resource.
get_deleter Returns the delete function
reset Resets the resource
swap Swaps the resources.
unique Checks if the std::shared_ptr is the exclusive owner of the resource.
use_count Returns the value of the reference counter.

Methods of `std::shared_ptr`

std::make_shared

The helper function std::make_shared creates the resource and returns it in a std::shared_ptr. You should use std::make_shared instead of the direct creation of a std::shared_ptr, because std::make_shared is a lot faster.

The following code sample shows a typical use case of a std::shared_ptr.

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