[C++-sig] why does the "shared_ptr<X> const&" silently become 0xCCCCCCCC

[ZaeX]

Hi,Roman:

I have tried adding call policy on my constructor, but I'm really no good at
this.
I have tried all the combinations below but none of them work:

   - init<shared_ptr<A> const& >()[with_custodian_and_ward_postcall<0, 2>
   >()]
   - init<shared_ptr<A> const& >()[with_custodian_and_ward_postcall<1, 2>
   >()]
   - init<shared_ptr<A> const& >()[return_internal_reference<1,
   with_custodian_and_ward<1, 2> >()]
   - init<shared_ptr<A> const& >()[return_internal_reference<1,
   with_custodian_and_ward<0, 2> >()]

Could you give some more advice on this?
P.S.:
I cannot modify the code back  to use shared_ptr by value here, I have to
break cyclic reference. And I think weak_ptr is no good idea, if I lock it
60 times per second for each object, I guess it would be an impact on
performance.

On Wed, Mar 11, 2009 at 2:19 PM, Roman Yakovenko
<roman.yakovenko at gmail.com>wrote:

> 2009/3/11 ZaeX <zaexage at gmail.com>:
> > Hi, All:
> >
> > I used a "shared_ptr<A> const&" to store a ref of A in B;
> > Well, the constructor of B seems ok, the share_ptr<A> seems to be well
> > initialized;
> > but after the constructor, I found the the pointer silently become
> > 0xCCCCCCCC
> >
> > ///////////////////////////////////// below are the simplified class
> > definitions
> > class A{};
> >
> > class B
> > {
> > private:
> >    shared_ptr<A> const& m_ptr;
> > public:
> >    B(shared_ptr<A> const& ptr):m_ptr(ptr) {cout<<m_ptr.get()<<endl;}
> >    void ShowPtr(cout<<m_ptr.get()<<endl;)
> > }
> > /////////////////////////////////// below are my exporting code
> >
> >     class_<B, auto_ptr<B> >("B",  init<shared_ptr<A> const&>())
> >        .def("ShowPtr", &B::ShowPtr)
> >     ;
> >     class_<A, shared_ptr<A>, noncopyable >("A")
> >     ;
> > /////////////////////////////////// below are python code
> >  a = A()
> >  b = B(a)  #cout output the ptr of a
> >  b.ShowPtr()  #cout output 0xCCCCCCCC
> >
> > ============================================
> > I'm quite confused by the behaviors here. Could you tell me what goes
> wrong?
>
> You have to bind lifetime argument to the lifetime of the created
> object:
> http://www.boost.org/doc/libs/1_38_0/libs/python/doc/tutorial/doc/html/python/functions.html#python.call_policies
>
> Constructors also have call policies and you can use them.
>
> Anyway, you will save to yourself a lot of time, if you will use
> shared_ptr by value. I suggest you to change your code.
>
> --
> Roman Yakovenko
> C++ Python language binding
> http://www.language-binding.net/
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-- 
Time is mana, we must hurry
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