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Manoj Rao

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C++11 introduced four different Smart Pointers because when it came to pointers, everybody was sick of you whining about one of the following

  • We couldn’t figure out if the pointer was pointing to a single object or a whole lot of them
  • We didn’t use const while passing these pointers around, there was no clear policy implicit in the code, so we could not tell if we could delete an object pointed to by the pointer.
  • We kept deleting it multiple times and you wouldn’t set it to NULL after deleting it once.

Four Smart Pointers

That’s right! to help us from getting out feet stuck in the ceiling fans the C++ language introduced four smart pointers:

  • std::unique_ptr
  • std::shared_ptr
  • std::weak_ptr
  • std::auto_ptr

std::unique_ptr

They are exactly what they sound like. Such pointers are meant to show that the memory pointed to by them are exclusively owned by the pointer. Therefore, the software deleting this memory must do so via this unique pointer. This is the most intuitive of the four smart pointers since it is more or less same as a raw pointer.

std::shared_ptr

This is C++’s answer to Java’s long sporadic blocking runs that take up CPU, usually, when you most need it since that’s also the time when the system is under a resource crunch. Sorry, that was a diss but an accurate one. Platform Developers and Low Level System Developers on Android Developers will share their scars about this in their chapter of AA (Androiders Anonymous?).

Before Smart Pointing, C++ used to leave the responsibility to the developer to delete objects. But developers are not adults, we just want our outputs, we are not deleting stuff! even if we did we would delete it awkwardly enough to cause troubles for 20 years. Or at least, that seemed to be the attitude. Basically, C++’s efficiency came from the fact that there were no training wheels. The developer was always expected to keep track of resources allocated in their programs. This took sufficient time away from making the core logic more robust.

But what is C++’s response? It’s basically same as what was done earlier except with basic ref counting implemented in the shared pointer it is possible to keep track of all active referrers to the object and simply call the supplied or default constructor. Actually, that’s pretty clever! You are getting the best of both worlds in this case, right? The trade-off is that this smart pointer requires additional memory for keeping ref count and requires updates to the ref counter be via atomic operations.

std::weak_ptr

If your std::shared_ptr can dangle after deletion, use std::weak_ptr. Doing supports APIs that can explicitly tell you whether this is a bad idea or not.

When possible, it is recommended to use std::make_unique and std::make_shared instead of new

Sources:

  • Effective Modern C++

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