CODEWITHSUNDEEP
c++boostcastingshared-ptr
Max Frai
Max Frai

Reputation: 64266

shared ptr casting

class Object { };
Class Derived : public Object { };

boost::shared_ptr<Object> mObject(new Derived); // Ok

But how to cast it to boost::shared_ptr<Derived> ?

I tried something like: static_cast< boost::shared_ptr<Derived> >(mObject) and it failed.

The only working idea is:

boost::shared_ptr<Derived> res(new dynamic_cast<Derived*>(mObject.get()))

Upvotes: 3

Views: 10691

Answers (2)

Jianjun Liu
Jianjun Liu

Reputation: 19

You can try

class Object { };
Class Derived : public Object { };

boost::shared_ptr<Object> mObject = new Derived; // OK
boost::shared_ptr<Derived> mDerived = 
    boost::static_pointer_cast<Derived, Object>(mObject); // OK

Boost has the corresponding templates to fulfill the standard casts defined in c++.

Upvotes: 0

bdonlan
bdonlan

Reputation: 231093

DO NOT pass the result of the cast to a new shared_ptr constructor. This will result in two shared_ptrs thinking they own the object, and both will try to delete it. The result will be a double-free, and a likely crash.

shared_ptr has cast functions specifically for this.

Upvotes: 12

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