CODEWITHSUNDEEP
c++smart-pointersunique-ptr
perreal
perreal

Reputation: 97918

How to return a pointer to a unique_ptr wrapped pointer

How can I create a pointer to a pointer that is wrapped inside a unique_ptr? In other words, is there a sound way to write this function:

int **getIterator(std::unique_ptr<int>& p)
{
     /* error: lvalue required as unary ‘&’ operand */
     return &p.get();
}

Upvotes: 0

Views: 823

Answers (1)

Mateusz Grzejek
Mateusz Grzejek

Reputation: 12058

I want to return a pointer to use as an iterator with an interface that expects iterators. I want to pass algo(getIterator(X), getIterator(X)+1) so that single items look like collections.

You are using std::unique_ptr<int>. If I understand your problem correctly, you are trying to do something, that is not necessary in this case: if you want to iterate through ints, you need int* (pointer to object), not int** (pointer to pointer).

Use this:

int* getIterator(std::unique_ptr<int>& p)
{
     return p.get();
}

Then, you can do what you wanted:

algo(getIterator(X), getIterator(X) + 1);

I expect algo being defined similar to this:

template <class Iter>
Result_type algo(Iter begin, Iter end)
{
  //algorithm
}

If you do something like:

std::unique_ptr<int> p = /* initialize */;
algo(getIterator(p), getIterator(p) + 1);

You will receive two parameters of type int*, that can be safely moved forward/backward and dereferenced to get current object's value.

Upvotes: 2

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