CODEWITHSUNDEEP
c++
Christopher Pisz
Christopher Pisz

Reputation: 4010

shared_from_this when inheriting from class defined by third party

I've read many posts on stack-overflow about shared_from_this, bad_weak_ptr exceptions, and multiple inheritance while trying to research my problem. All of them propose you inherit a base class from enable_shared_from_this, and then derive from that. Well, what does one do when the class you have to derive from is a coming from a third party library that you cannot edit?

Example:

#include <iostream>
#include <memory>

class ThirdPartyClass
{
public:
    ThirdPartyClass() {}
    ThirdPartyClass(const ThirdPartyClass &) = delete;
    virtual ~ThirdPartyClass() {};
};

class A : public ThirdPartyClass, std::enable_shared_from_this<A>
{
public:
    A():ThirdPartyClass(){}
    virtual ~A(){}

    void Foo();
};

void DoStuff(std::shared_ptr<A> ptr)
{
    std::cout << "Good job if you made it this far!" << std::endl;
}

void A::Foo()
{
    DoStuff(shared_from_this());    // throws here
}

int main() {
    std::shared_ptr<A> a = std::make_shared<A>();
    a->Foo();
    return 0;
}

Upvotes: 1

Views: 157

Answers (1)

dewaffled
dewaffled

Reputation: 2973

You get the error because you are not public inheriting from enable_shared_from_this and shared_ptr and make_shared cannot detect that the object requires such support. Not because of inheritance from third party class.

So, to fix just inherit as public:

class A : public ThirdPartyClass, public std::enable_shared_from_this<A>

Upvotes: 1

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