Re: [Boost-users] shared_ptr/shared_array Question

From: cyril.godart_at_[hidden]
Date: 2004-02-26 04:12:35

Hi,

I suggest the following code:

class Master
{
      typedef boost::smart_ptr<Slave> slave_ptr_t;
      typedef boost::smart_ptr<const Slave> slave_cst_ptr_t;

      typedef std::vector<slave_ptr_t> vec_slaves_t;
      typedef std::vector<slave_cst_ptr_t> vec_cst_slaves_t;//defining this
one is good practice as you'll see later

      Master();
      Master(size_t i)
      {
            slaves_.resize(i);// assume slave has an empty ctor defined.
      }

      vec_cst_slaves_t slaves() //something like const vec_cst_slaves_t&
slaves() const should work
      {
          return slaves_; //nice casting that I failed to notice until
someone in this list mentioned it to me
      };

      vec_slaves_t slaves_;
};

As you rightly guessed, a big advantage of this approach is that the
plumbing of copy-assigment
dtor and so on reduces drastically. I find it extremely convenient, even
though there is a performance
hit.

Regards,

Cyril Godart.

Internet
goochrules_at_[hidden]@lists.boost.org - 25/02/2004 21:09

Please respond to boost-users_at_[hidden]

Sent by:    boost-users-bounces_at_[hidden]

To:    boost-users

cc:

Subject:    Re: [Boost-users] shared_ptr/shared_array    Question

On Feb 25, 2004, at 12:27 PM, voodoo4 wrote:

> I downloaded yesterday the boost libraries (mainly for the memory
> libs) and
> to tell the truth i'm impressed with pool and smart pointers.
> Especially the boost smart pointers will save me from months of coding!
> However i have a question about smart pointers.
>
> Let's say i have these objects(the code is just an example):
>
> class Slave
> {
> Slave();
> ~Slave();
> };
>
> class Master
> {
> Master();
> Master(int size);
> ~Master();
>
> Slave *sl;
> };
>
> I want "sl" to be an array of Slaves on the free store but the sized
> will be
> determined in the constructor.
>
> With normal pointers i would write:
>
> Master::Master(int val)
> {
> sl=new Slave[val];
> }
>
> Master::~Master()
> {
> delete sl;
> }
>
>
> How can i achieve the same with boost smart pointers?

I have no idea (see below).

> I've read the manual three or four times but i still don't get how to
> work
> this out.
> Does this have something to do with the empty ptr?
> I believe solution is in front of my eyes but i'm too blind(as usual)
> to see
> it...
>

I don't think you're using the right tool for the job.  From what I
know, smart pointers should be used when you have one object, here you
(potentially) have many.  I think what you really want to do here is to
use a container class like stl::list or stl::vector to contain your
slave objects.

If you still want to use smart pointers, I guess you could use a list
of smart pointers, but there's really no point for that if your slave
class is properly coded (for instance, has a ctor, copy ctor, virtual
dtor, and operator=).

--MP

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