Menu
I have a question about C++11 best practices. When clearing a shared_ptr, should I use the reset() function with no parameter, or should I set the shared_ptr to nullptr? For example:
std::shared_ptr<std::string> foo(new std::string("foo")); foo.reset(); foo = nullptr; Is there any real difference, or are there advantages/disadvantages to either approach?
944
If shared_ptr::unique returns true, then calling shared_ptr::reset will delete the managed object.
A null shared_ptr does serve the same purpose as a raw null pointer. It might indicate the non-availability of data. However, for the most part, there is no reason for a null shared_ptr to possess a control block or a managed nullptr .
std::shared_ptr<T>::reset. Replaces the managed object with an object pointed to by ptr . Optional deleter d can be supplied, which is later used to destroy the new object when no shared_ptr objects own it. By default, delete expression is used as deleter.
Use unique_ptr when you want a single pointer to an object that will be reclaimed when that single pointer is destroyed. Use shared_ptr when you want multiple pointers to the same resource.
Is there any real difference, or are there advantages/disadvantages to either approach?
The two alternatives are absolutely equivalent, in the sense that the second form (foo = nullptr) is defined in terms of the first one. Per Paragraph 20.7.1.2.3/8-10 of the C++11 Standard:
unique_ptr& operator=(nullptr_t) noexcept;8 Effects:
reset().9 Postcondition:
get() == nullptr10 Returns:
*this.
Therefore, just choose the one which makes its intent clearest for you. Personally, I prefer:
foo = nullptr; Because it makes it more evident that we want the pointer to be null. As a general advice, however, try to minimize the situations where you need to explicitly reset a smart pointer.
Besides, rather than using new:
std::shared_ptr<std::string> foo(new std::string("foo")); Consider using std::make_shared() when possible:
auto foo = std::make_shared<std::string>("foo"); If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
