# C++ Smart Pointers Smart pointers have existed almost as long as C++, but have recently gained attention as worries about memory safety becomes more commonplace. The idea of a smart pointer is that they are a wrapper around a raw pointer, which will automatically be freed once it stops being used (like a standard pointer in Rust). `unique_ptr` allows for exactly one owner of the underlying pointer, and while ownership can be transferred to other `unique_ptr` objects, the pointer cannot be copied or shared. Once a `unique_ptr` goes out of scope, the underlying pointer (if it still exists) is freed to clean up. If ownership was transferred to another `unique_ptr`, then there is no underlying pointer, and nothing happens. The original raw pointer is not freed until the new owning `unique_ptr` is out of scope. `shared_ptr` is different and allows for multiple owners. The raw pointer is not deleted until **all** `shared_ptr` owners are out of scope (or otherwise given up ownership). To do this, a `shared_ptr` also has a **shared** [**reference count**](/notes/binexp/memory-safety/garbage-collection/automatic-reference-counting.md) which is decremented every time a `shared_ptr` goes out of scope, is reset or is overwritten. Once it drops to zero, the raw pointer is freed. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://ir0nstone.gitbook.io/notes/binexp/memory-safety/c++-smart-pointers.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.