memory_resource* new_delete_resource() noexcept;
Returns: A pointer to a static-duration object of a type derived from memory_resource that can serve as a resource for allocating memory using ::operator new and ::operator delete. The same value is returned every time this function is called. For a return value p and a memory resource r, p->is_equal(r) returns &r == p.
memory_resource* null_memory_resource() noexcept;
Returns: A pointer to a static-duration object of a type derived from memory_resource for which allocate() always throws bad_alloc and for which deallocate() has no effect. The same value is returned every time this function is called. For a return value p and a memory resource r, p->is_equal(r) returns &r == p.
The default memory resource pointer is a pointer to a memory resource that is used by certain facilities when an explicit memory resource is not supplied through the interface. Its initial value is the return value of new_delete_resource().
memory_resource* set_default_resource(memory_resource* r) noexcept;
Effects: If r is non-null, sets the value of the default memory resource pointer to r, otherwise sets the default memory resource pointer to new_delete_resource().
Postconditions: get_default_resource() == r.
Returns: The previous value of the default memory resource pointer.
Remarks: Calling the set_default_resource and get_default_resource functions shall not incur a data race. A call to the set_default_resource function shall synchronize with subsequent calls to the set_default_resource and get_default_resource functions.
memory_resource* get_default_resource() noexcept;
Returns: The current value of the default memory resource pointer.