Re: [boost] Intrusive smart pointer

From: Darin Adler (darin_at_[hidden])
Date: 2002-04-19 16:10:23

On Friday, April 19, 2002, at 01:42 PM, Peter Dimov wrote:

> From: "Fernando Cacciola" <fcacciola_at_[hidden]>
>>  int main()
>> {
>>   boost::intrusive_ptr<X> px(new X);  // obj's internal count=1
>>   boost::intrusive_ptr<X> px2(px); // obj's internal count=2
>>   boost::shared_ptr<X> px3(px2); // obj's internal count still =2, 
>> detached count=1
>>
>>   px = 0; // obj's internal count=1
>>   px2 = 0; // obj's internal count=0  -----> obj suicides itself....
>>
>> *px3 ;  // undefined behavior, pointee no longer alive.
>>  }
>>
>> What I am missing?
>
> Try it. :-)

What Peter means is:

     1) If X is publicly derived from shared_count, it will just work, 
because shared_ptr will find the shared_count part and use it for 
reference counting. There won't be a "detached count".

     2) If X is not publicly derived from shared_count, then the 
shared_ptr constructor for px3 will fail to compile.

Now you should try it and see that it works as designed.

     -- Darin