When shared_ptr is created via one of the shared_ptr constructors, the managed object and the control block must be allocated separately. The managed object is constructed in-place in a data member of the control block. When shared_ptr is created by calling std::make_shared or std::allocate_shared, the memory for both the control block and the managed object is created with a single allocation. the number of weak_ptrs that refer to the managed object.the number of shared_ptrs that own the managed object.either a pointer to the managed object or the managed object itself.The control block is a dynamically-allocated object that holds: the stored pointer (one returned by get()).In a typical implementation, shared_ptr holds only two pointers: Std :: shared_ptr ee (fun, del ) ( *ee ) ( ) } Implementation notes If multiple threads of execution access the same shared_ptr object without synchronization and any of those accesses uses a non-const member function of shared_ptr then a data race will occur the std::atomic can be used to prevent the data race. The managed pointer is the one passed to the deleter when use count reaches zero.Ī shared_ptr may also own no objects, in which case it is called empty (an empty shared_ptr may have a non-null stored pointer if the aliasing constructor was used to create it).Īll specializations of shared_ptr meet the requirements of Cop圜onstructible, CopyAssignable, and LessThanComparable and are contextually convertible to bool.Īll member functions (including copy constructor and copy assignment) can be called by multiple threads on different shared_ptr objects without additional synchronization even if these objects are copies and share ownership of the same object. The stored pointer is the one accessed by get(), the dereference and the comparison operators. This feature can be used to point to member objects while owning the object they belong to. The object is destroyed using delete-expression or a custom deleter that is supplied to shared_ptr during construction.Ī shared_ptr can share ownership of an object while storing a pointer to another object. the last remaining shared_ptr owning the object is assigned another pointer via operator= or reset().the last remaining shared_ptr owning the object is destroyed.The object is destroyed and its memory deallocated when either of the following happens: Several shared_ptr objects may own the same object. Std::shared_ptr is a smart pointer that retains shared ownership of an object through a pointer.

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