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Observer_ptr in C++

A C++ smart pointer called std::observer_ptr was included in the C++ Standard Library and debuted in C++20. It is intended to serve as a thin, non-owning reference to an item. The std::observer_ptr is used to signify that a segment of code observes something without assuming any responsibility for it or exerting any control over its existence. It is beneficial to reliably refer to an object without managing its memory.

Attributes of std::observer_ptr function:

There are several attributes of the std::observer_ptr. Some main attributes of the std::observer_ptr function are as follows:

  • Absent-owner: Unlike std::shared_ptr or std::unique_ptr, which control the referenced object's lifespan, it does not take part in the ownership of the object it points to.
  • Not heavy: It has extremely little memory overhead and is a very light pointer. Unlike other smart pointers, it does not have the overhead of ownership monitoring or reference counting.
  • Has no impact on item lifetime: The life span of the object pointed to by std::observer_ptr is not extended. If the object it is observing is removed or moves out of scope, the observer reference remains valid, even though it may be pointing to a potentially erroneous memory address. It is the responsibility of programmers to ensure that an object has a lifespan.


Here's a simple example of using std::observer_ptr:


  • In this example, the std::observer_ptr obs_ptr points to the integer x, but it does not affect on x's lifetime. The observer pointer allows you to see your changes to x.
  • When you require non-owning references to objects while indicating the lack of ownership, std::observer_ptr is useful. Common issues like dangling pointers and accessing things that have left their scope can be avoided with its assistance.

Benefits of Observer_ptr in C++

C++'s std::observer_ptr provides several advantages when it comes to non-owning, lightweight object observation. The following are some of the main benefits of using std::observer_ptr:

  • The semantics of non-owning: The std::observer_ptr explicitly states that it is not the owner of the observed object. It promotes the intention of non-ownership and helps to prevent accidental ownership transfers, both of which are beneficial for the readability and maintainability of the code
  • Safety: It helps avoid frequent problems with raw pointers, including pointers that dangle. Using std::observer_ptr leaves the owner code controlling the object's lifetime. The observer pointer is safer than raw pointers since it points to potentially faulty memory if the observed object is removed or goes out of scope.
  • Lightweight: Regarding memory use and computational overhead, std::observer_ptr is a highly light pointer. It does not carry the extra ownership tracking and reference counting information in smart pointers like std::shared_ptr and std::unique_ptr.
  • Expressiveness: It enables you to precisely communicate your intentions in the code. You are obviously viewing an item without owning it when you use std::observer_ptr. It can improve the code's readability and self-documentation.
  • Compatibility: It is made to function nicely with interfaces and codebases that already exist. When working with historical code or libraries that don't support C++ smart pointers, you can use the std::observer_ptr in conjunction with other smart pointers or raw pointers.
  • Interoperability: It can be helpful when working with C libraries or other languages that frequently use raw pointers. Type safety in C++ can still be utilized when interacting with objects maintained by these libraries by using std::observer_ptr.
  • Safety and debugging improvements: You can discover problems at build time or get more detailed runtime diagnostics when you try to access an object that has left its scope by using std::observer_ptr.

In general, std::observer_ptr is a valuable addition to C++ that improves the expressiveness and safety of your code, especially when you need to represent non-owning references to objects. It encourages improved practices and assists in avoiding typical mistakes related to ownership management and raw pointers.

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