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Discussion on: Memory management using Smart Pointers in C++ - Part 2

sandordargo profile image
Sandor Dargo • Edited

Thanks for the article.

I have two remarks.

1) When you delete a derived class through a base class pointer where the base class has no virtual destructor, that is not a partial deletion. It's undefined behaviour which is much worse. More info here.

2) Passing around a smart pointer by reference to gain on the performance is not a good idea. We've seen this with a colleague of mine and we found that the reason behind is a lack of understanding.


What's the purpose of using a smart pointer?

It's to handle ownership in a safe way. That's why you use smart pointers. If you pass around a reference, you don't pass/share the ownership.

If ownership is not involved, there is no need for smart pointers. Instead, you should just pass around a pointer.

It will be even faster because there is less indirection. Plus you don't have to make the mental exercise of understanding what a reference of a pointer mean.

Fast pointer

QuickBench here.

(You don't need an inner loop in QuickBench. With for (auto _ : state) it takes care of executing things enough)

pratikparvati profile image
Pratik Parvati Author

Thanks for your remarks Sandor.

I understand your point on ownership semantics of the objects; It completely makes sense to pass smart pointers by value. My intension was to point out the overhead added by the atomic operations (increment and decrement reference count) in shared_ptr; perhaps, I should edit and make this point clear.

sandordargo profile image
Sandor Dargo

What should be made clear IMO is that there is no good reason to pass a smart pointer by reference.

If you refer to Herb Sutter, he recommends that you "don’t pass a smart pointer as a function parameter unless you want to use or manipulate the smart pointer itself, such as to share or transfer ownership".

Consider that and knowing that sharing a smart pointer by reference doesn't share or transfer the ownership, we have no reasons to pass a SP by reference.

Some corresponding rules: