Best way to use C ++ interface

Question

I have an interface class similar to:

class IInterface
{
public:

    virtual ~IInterface() {}

    virtual methodA() = 0;

    virtual methodB() = 0;

};

Then I implement the interface:

class AImplementation : public IInterface
{
    // etc... implementation here
}

When I use the interface in an application, it is better to instantiate a specific AImplementation class. For example.

int main()
{
    AImplementation* ai = new AIImplementation();
}

Or it is better to place the factory create function in the interface, as shown below:

class IInterface
{
public:

    virtual ~IInterface() {}

    static std::tr1::shared_ptr<IInterface> create(); // implementation in .cpp
    virtual methodA() = 0;

    virtual methodB() = 0;

};

Then I could use the interface basically like this:

int main()
{
    std::tr1::shared_ptr<IInterface> test(IInterface::create());
}

The first option seems common practice (not to mention his right). However, the second option was obtained from Effective C ++.

Answer 1

One of the most common reasons for using an interface is that you can "program against abstraction," rather than a specific implementation.

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Answer 2

, :

int main(int argc, char* argv[])
{
   //...
   boost::shared_ptr<IInterface> test(new AImplementation);
   //...
   return 0;
}

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