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[C++] Inheritance not working from constructor?

fyhuang · 2005-07-22T14:19:47

Hey all, I'm having this small problem with my code - I have a base Singleton class (not a complete code listing): class Singleton { public: void create(); virtual int init() { return 0; } virtual int shutdown() { return 0; } protected: Singleton() { init(); } virtual ~Singleton() { shutdown(); } }; The purpose of this code is, when the Singleton is created, the init() function is called to perform initialization, and when it is destroyed, the shutdown() function is called to perform shutting-down. Classes that inherit from Singleton can override init() and shutdown(). My problem is - I have a derived class that overrides both init() and shutdown(), but when the Singleton is created, the base Singleton's init() function is called instead of the overridden init() function (obviously I want the overridden one to be called). Not implementing init() and shutdown() in Singleton of course causes the compiler to tell me that, I can't use those functions in the constructor/destructor because they're not defined. Since there's some error-checking code wrapping init() and shutdown() (not shown here), I don't want to copy & paste the constructor code to each derived class. Can anyone help me get this working? Thanks in advance!

General and Gameplay Programming Programming

Started by fyhuang July 21, 2005 07:04 PM

10 comments, last by fyhuang 18 years, 9 months ago

angry

128

July 22, 2005 05:58 AM

I think you can do it this way, though it will requier the use of templates:

template <typename T>class A{ public:    void printHello() { std::cout << "A::printHello()" << std::endl; }    A()    {       static_cast<T*>(this)->printHello();    }};class B: public A<B>{  public:     void printHello() { std::cout << "B::printHello()" << std::endl; }};B b; // outputs "B::printHello()"

The problem with this is that the printHello() method must be public, which is not always what you want.

fyhuang

253

Author

July 22, 2005 02:19 PM

Hey all,

I eventually implemented JohnBolton's suggestion, and it appears to work well enough. Mattnewport, I think I'm going to implement yours too, cause now that I think of it I don't see any reason for keeping the destruction code in shutdown(). I still think it's important to keep init code in init() so that, if something goes wrong, at least the object is fully constructed and I can now safely return an error, throw an exception, whatever. That's just me though.

Thanks and cheers!

- fyhuang [ site ]

[C++] Inheritance not working from constructor?

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[C++] Inheritance not working from constructor?

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