[c++0x] shared_ptr get() and use_count() inconsistency

Rodolfo Lima rodolfo@rodsoft.org
Thu Jun 5 18:15:00 GMT 2008

Peter Dimov escreveu:

>> The current standard draft says that use_count() should return 0 if 
>> the shared_ptr is empty, and get() should return NULL if the 
>> shared_ptr is also empty.
> http://www.open-std.org/JTC1/SC22/WG21/docs/lwg-active.html#711

Thanks Peter. But I prefer the second solution you gave because it would 
lead to, IMHO, a sane smart pointer semantics.

Say you want to pass a weak_ptr to a function but only if it points to a 
not empty shared_ptr. One might write:

void func(std::weak_ptr<int> x) {}

std::shared_ptr<int> aux();
int i;
std::shared_ptr<int> sptr(aux, &i);


In this case func would receive an weak_ptr that doesn't point to 
anything, although it was coded to not allow this, I mean, one would 
expect that if ptr.use_count()==0, (bool)ptr == false, but this doesn't 
hold above.

I know this is offtopic to this list, so I'm moving this to 

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