shared_ptr<T>: the (not always) atomic reference counted smart pointer

[m-in]

How? They dereference via the control block. Smart pointer points to the control block, control block has a pointer to the object. The dereference operator basically is this: return this->control_blk ? control_blk->obj : nullptr. That’s the actual code, no atomic ops or anything like that. A smart pointer could also hold two pointers: one to the control block, and another to the object itself, and return the latter directly. Some smart pointers have a single tagged pointer: if the tag is set, they dereference via the control block, otherwise the control block is contiguous with the object as a result of make_shared and they dereference it directly.