QCache and std::shared_ptr

Question

Can someone give me please a hint for this error:

no viable conversion from 'std::shared_ptr<Foo>' to 'std::__1::shared_ptr<Foo> *'

The QCache looks like this:

QCache<int, std::shared_ptr<Foo>> cache;

And I try to insert the element like this:

std::shared_ptr<Foo> foo;
cache.insert(23, foo);

Thanks for your help.

From the error it seems like QCache wants a pointer to it's stored type, not the type itself. — SergeyA
– SergeyA, Commented Oct 15, 2015 at 20:30
Thanks. It compiles now as a reference with: cache.insert(23, &foo); ... but I'm not sure if the smart pointer counts this reference. — adapto
– adapto, Commented Oct 15, 2015 at 20:34

SergeyA · Accepted Answer · 2015-10-15 20:33:33Z

3

Just looked into QCache API, and since my guess is correct, I will post it as an answer (with hopes for upvotes!).

Signature for insert() is bool QCache::insert(const Key & key, T * object, int cost = 1). Moreover, API mentions the fact that QCache owns the pointer from that moment on, so you do not need shared_ptr at all. Instead, you should insert raw pointer which will be managed by QCache.

answered Oct 15, 2015 at 20:33

SergeyA

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4 Comments

adapto Over a year ago

Thanks for the answer and the help.

adapto Over a year ago

The problem is, that I have a vector of shared_ptr and I want to put part of them to my QCache. What happens if I set the pointer to my cache but destroy the vector and the shared pointer in it? WIll the memory be released and my cache points to nowhere?

SergeyA Over a year ago

@adapto, you will have a corrupted program if you try to do this. You can't have the same pointer owned by two managers - QCache and shared_ptr.

Orest Hera Over a year ago

That caused the confusion: stackoverflow.com/questions/33280524/qcache-and-qsharedpointer

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