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

Subject: Re: [Boost-users] shared_ptr to stack-allocated object
From: Jason Cipriani (jason.cipriani_at_[hidden])
Date: 2008-12-04 19:42:38

On Thu, Dec 4, 2008 at 7:22 PM, Emil Dotchevski <emil_at_[hidden]> wrote:
> On Thu, Dec 4, 2008 at 4:03 PM, Jason Cipriani <jason.cipriani_at_[hidden]> 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.