Re: [Boost-users] shared_ptr to stack-allocated object

On Thu, Dec 4, 2008 at 7:22 PM, Emil Dotchevski wrote:

On Thu, Dec 4, 2008 at 4:03 PM, Jason Cipriani wrote:

...

I'm refactoring parts of an existing application to use shared_ptrs instead of raw pointers. What is the best way to deal with code like this (please note in this situation passing a pointer to a stack-allocated object to function is acceptable and safe):

void function (shared_ptr<Object> ptr) { ... }

void function2 () { Object o; function(&o); // <--- need to change this }

It seems I have two choices, I am not sure which is better, or if there are other common techniques. I can either use a no-op delete function:

void noop (Object *) {}

void function2 () { Object o; function(shared_ptr<Object>(&o, noop)); }

Or I can allocate it on the heap instead of the stack, and let shared_ptr deal with the cleanup (this seems to be the more convenient solution):

void function2 () { shared_ptr<Object> o(new Object); function(o); }

What's the normal practice here?

I'm not sure what's normal, but if your function isn't going to take ownership of the object you're passing (which in this case it can't do anyway since the object is allocated on the stack), it should take Object &, not shared_ptr<Object>.

Even if it must take shared_ptr<Object> for some reason, it's better to take shared_ptr<Object> const &, to avoid the refcount increment/decrement (in general, I can't think of a reason to pass shared_ptr by value.)

Thanks for the tip. In this case, function needs to take a shared_ptr as it is used in other contexts with shared_ptr's, it's only sometimes used with objects from the stack.