Why scoped pointers in boost
What is the objective of scoped pointer? to my understanding, the scoped pointer manages the memory within a block of code. If i want to declare a variable within a block , i can just declare it on a stack and not worry about cleaning.
Not if it's of dynamic size or type. In addition, scoped pointers can be swapped, and in C++11 unique_ptr can be moved, so they're not strictly scoped.
Unlike stack-based data, scoped_ptr has a reset() member -- in other words, you can construct/destruct to your heart's content. With this, you can use a null pointer (technically operator unspecified-bool-type ) as a flag indicating whether or not there is a constructed object at any given time. It also allows you to sequence construction/destruction independently from the variable scope if that is needed.
Also, consider that you can declare a scoped_ptr as a class member, not just as a stack variable. The docs suggest using scoped_ptr to implement the handle/body idiom (to hide the class' implementation details).
Finally, to elaborate on DeadMG's point "Not if it's of dynamic type", you can use scoped_ptr to implement a polymorphic operation:
{
scoped_ptr<Base> a( mode ? new DerivedA : new DerivedB );
a->polymorphic_function();
}
It's not really possible to do this with simple stack-based allocation.
Also see here: C++0x unique_ptr replaces scoped_ptr taking ownership?
The point is that you can create and clean up a pointer within a certain lexical scope. This can be useful in a variety of situations, and it assures you have no memory leaks, by forgetting a delete if you were to use new explicitly, which is not recommended.
You should keep in mind that the boost::scoped_ptr is non-copyable , and so owns it's resource entirely, for the entire duration of it's lifetime. This also makes it safer then boost::shared_ptr , as it avoids copying the resource or accidentally sharing it.
{ //Some Scope
boost::scoped_ptr<int> i_ptr;
// do something with pointer
} // leave scope, pointer is cleaned up
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