Smart pointer vs owning raw pointer

Question

As far as I know, it's preferred to use a smart pointer instead of managing the lifetime of a dynamically allocated object through a raw pointer, e.g.: MyObject* obj = new Object();

But in some frameworks/libraries they always return/work with raw pointers instead of smart pointers, (maybe they have their own GC objects? I don't know).

It's also easier to work with

 MyObject* obj = GetAObject(); // return raw owning pointer

than

SharedPointer<MyObject> obj = GetAObject(); // return smart pointer

Should one always use smart pointers instead of manual new/delete (like in the example above) or are there any cases where raw resource-owning pointers should be used?

``new`` is not the opposite option of smart pointers. Naked pointers are the opposite of smart pointers. — Ami Tavory, Jun 08 '15 at 14:41
It sounds like you heard it's preferred to use a smart pointer and took that advice to heart without understanding it. Please don't do that. Go back to where you saw that and read and understand the reasoning. You won't have this question after you do so. — R. Martinho Fernandes, Jun 08 '15 at 14:41
While this question probably could be rephrased to be more objective, it probably would become a duplicate in the process. — MSalters, Jun 08 '15 at 14:42
@R.MartinhoFernandes: It was probably one of Puppy's stupid generalising comments on someone's prior SO question. — Lightness Races in Orbit, Jun 08 '15 at 14:47
This might be helpful: [When should I use raw pointers over smart pointers?](http://stackoverflow.com/q/6675651/3425536) — Emil Laine, Jun 08 '15 at 15:00

Baum mit Augen · Answer 1 · 2016-12-31T12:21:37.120

6

If your code is not required to compile with a pre-C++11 compiler, I see no reason to have owning raw pointers.

Even if your code needs to compile with ancient compilers, you should check out the smart pointers from Boost.

I do not know of a single situation in which an owning raw pointer would be a good idea.

Nothing wrong with non-owning raw pointers if appropriate.

It is true that a lot of code still uses owning raw pointers. This should fall mainly into two categories:

Code older than Boost smart pointers/C++11
Code written by people who do not follow modern C++ best practice.

edited Dec 31 '16 at 12:21

answered Jun 08 '15 at 14:39

Baum mit Augen

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or really old codebase. – Abhinav Gauniyal Jun 08 '15 at 14:46
@AbhinavGauniyal Re-read my answer. :P – Baum mit Augen Jun 08 '15 at 14:46
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What about pointers to hardware devices? Is that considered *owning* a raw pointer? – Thomas Matthews Jun 08 '15 at 14:49
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@ThomasMatthews If and only if some cleanup (like closing a connection or something like this) is required as soon as the pointer (and all of its co-owners, if any) expire I would say. But tbh I am not too sure what a pointer to a hardware device is in detail, I never had to deal with such things so far. – Baum mit Augen Jun 08 '15 at 14:51

score 6 · Answer 2 · answered Jun 08 '15 at 14:41

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Pointer usage should be informed by the ownership semantics you are trying to model in your application.

If your library returns raw pointers to memory which the library manages, then raw pointers are absolutely fine. If it returns pointers to memory which your application should own, then smart pointers are a better choice, because you can forget about the memory management and your intent is documented by the code.

answered Jun 08 '15 at 14:41

TartanLlama

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There is some ambiguity in semantics not supported by the language however. For example all weak_ptr can be converted to shared_ptr, potentially leading to "leaks" through cycles or resource contention issues if not properly managed. I asked a question about it some time ago. http://stackoverflow.com/questions/23016854/c-shared-ptr-vs-unique-ptr-for-resource-management – Robinson Jun 08 '15 at 14:55

score 1 · Answer 3 · answered Jun 08 '15 at 14:41

Working with smart pointer might saves you a lot of troubles chasing memory leaks. You can always wrap the pointers returned by a third party library into a smart pointer, but you need to be careful on who is really the owner of the allocated memory. You should read the library documentation to be sure that once you give the allocated memory to the smart pointer, someone else is not messing with it: for instance, as you suggested, if the framework has it's own garbage collector.

Smart pointer vs owning raw pointer

3 Answers3