CODEWITHSUNDEEP
c++shared-ptr
myWallJSON
myWallJSON

Reputation: 9502

How to get a reference to an object having shared_ptr to it?

How to get a reference to an object having shared_ptr<T> to it? (for a simple class T)

Upvotes: 20

Views: 18963

Answers (2)

dimo414
dimo414

Reputation: 48794

Is there a concept of shared refrence?

Yes actually! shared_ptr provides an "aliasing constructor" that can be used exactly for this purpose. It returns a shared_ptr that uses the same reference count as the input shared_ptr but points to a different reference, typically a field or value derived from the backing data.

It is the responsibility of the programmer to make sure that this ptr remains valid as long as this shared_ptr exists, such as in the typical use cases where ptr is a member of the object managed by r or is an alias (e.g., downcast) of r.get()

What is shared_ptr's aliasing constructor for? goes into this in more detail, including an example of how to use it.

Upvotes: 0

Corbin
Corbin

Reputation: 33437

operator* already returns a reference:

T& ref = *ptr;

Or, I suppose I could give a more meaningful example:

void doSomething(std::vector<int>& v)
{
    v.push_back(3);
}

auto p = std::make_shared<std::vector<int>>();

//This:
doSomething(*p);

//Is just as valid as this:
vector<int> v;
doSomething(v);

(Note that it is of course invalid to use a reference that references a freed object though. Keeping a reference to an object does not have the same effect as keeping a shared_ptr instance. If the count of the shared_ptr instances falls to 0, the object will be freed regardless of how many references are referencing it.)

Upvotes: 22

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