CODEWITHSUNDEEP
c++c++11nullsmart-pointersreturn-type
Govan
Govan

Reputation: 2129

returning an emptyObject instead of a reference to a vector

Giving two classes A and B which B has a uinque_ptr of A! 

class B {
    unique_ptr<A> a;
    B() {
    }
    ~B() {
    }
}

and A has a method returning a vector of unique_ptr of itself as below:

   vector<unique_ptr<A>> const& A::getObjects() const {
        return this->myVector;
    }

Now I want to implement a method in B which checks if the unique_ptr to A has been existing return the vector in A otherwise a reference to an empty vector or Null as error: 

 vector<unique_ptr<A>> const& B::getObjects()const{
    if (this->a.get()!=nullptr){
       return this->a->getObjects()
    }
   //ToDo an empty object or null
 }

My question is what can I return in function above? returning nullptr is giving an compile error. returning the code below:

vector result; return result;

will cause a warning: reference to local variable result returned [-Wreturn-local-addr]

and returning {} (return {}) give me another warning:

returning reference to temporary [-Wreturn-local-addr]

So my question is what can I return without giving a warning or an error?

Upvotes: 2

Views: 319

Answers (1)

πάντα ῥεῖ
πάντα ῥεῖ

Reputation: 1

So my question is what can I return without giving a warning or an error?

You can have a static vector<unique_ptr<A>> nullresult; in your function, and return that one in case:

vector<unique_ptr<A>> const& B::getObjects()const{
    static vector<unique_ptr<A>> nullresult;
    if (this->a.get()!=nullptr){
        return this->a->getObjects()
    }
    return nullresult;
 }

Upvotes: 3

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