[boost] Re: shared_ptr with 0 use_count

From: dynalink (dynalink_at_[hidden])
Date: 2003-02-10 12:13:00

I need to create a single instance of  X and have it disappear when the
final B pointer goes out of scope. The problem with this code is that A::m_X
immediately bumps the ref count and only goes out of scope on termination.

Here's a simple example:

class X;    // defined elsewhere; in my case wraps a classic C structure.
typedef boost::smart_ptr<X> X_ptr;

struct A {
    static X_ptr create() { if (!m_X.get()) m_X.reset(new X); return m_X; }
    static X_ptr m_X;
};

struct B {
    B() : m_A(A::create()){}
    X_ptr m_A;
};

int main (int, void** argv)
{
    B a;
    B b;
    B c;
    do_something();
}

Thanks,
Peter.

Peter Krnjevic
Dynalink Technologies

"Peter Dimov" <pdimov_at_[hidden]> wrote in message
news:002801c2d122$5d604a40$1d00a8c0_at_pdimov2...
> dynalink wrote:
> > Forgive me if this seems like a really basic question, but how does
> > one create a shared_ptr with an initial use count of zero?
>
> There is no way to create a shared_ptr with use_count of zero. Use_count()
> returns the number of shared_ptr instances sharing ownership. Use_count()
==
> 0 means that there are is no shared_ptr instance. If you are able to call
> shared_ptr::use_count(), you have a(t least one) shared_ptr.
>
> Zero can only be returned from weak_ptr::use_count(), and this means that
> all shared_ptr's have been destroyed.
>
> Why do you ask?
>
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