Re: Should the shared_ptr have release method?

From:
thiago_adams@hotmail.com
Newsgroups:
comp.lang.c++.moderated
Date:
7 Jan 2007 11:53:27 -0500
Message-ID:
<1168124487.255527.36580@v33g2000cwv.googlegroups.com>
Howard Hinnant wrote:

I can't help you today. But there is a C++0X solution to your problem.
I'm presenting it here so that you know a solution is on the way.
Unfortunately you'll still have to work out a workaround until your
vendor comes up to speed. But know that adding a release function to
shared_ptr (which is also std in C++0X) may not be the best interim
workaround since by the time we get std::shared_ptr, we should also have
the functionality below:


Yes, I agree. I think that the release function in shared_ptr is not
necessary considering the existence of the unique_ptr.
The solution using moving semantics is really elegant.

I had one more idea to implement this function. The auto_ptr solves the
exception safe problem for one item very well. All we need is to solve
the problem for N items.
So, I have tested a recursive functions to create N auto_ptrs and it
works fine. I am now trying to generalize this recursive functions to
be used as an algorithm to create/insert objects into containers.
(Maybe this solution is efficient as well)

struct Item
{
    int i;
    Item(int i) : i(i)
    {
        cout << "constructing item " << i << endl;
        if (i == 5) throw std::exception("Exception to test fail");
    }
    ~Item()
    {
        cout << "destroying item " << i << endl;
    }
};

void CreateItem(vector<Item*> & vec, int & n)
{
    if (n == 10)
        return;
    auto_ptr<Item> ap(new Item(n));
    vec.push_back(ap.get());
    n++;
    CreateItem(vec, n);
    ap.release();
}

void GetItems(vector<Item*> &vec)
{
    vector<Item*> local;
    int i = 0;
    CreateItem(local, i);
    local.swap(vec);
}

int main()
{
    vector<Item*> items;
    try
    {
        GetItems(items);

        vector<Item*>::iterator it = items.begin();
        for( ; it != items.end(); ++it)
            delete *it;
    }
    catch(const std::exception & e)
    {
        cout << e.what();
    }
}

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