c++ - Access "this" pointer of concrete class from interface -

after writing test, determined this pointer in interface not equal this pointer of concrete class, meaning can't use c-style cast on it.

class abstractbase {...};  class aninterface { public:     aninterface() {...} // need abstractbase * here      ~virtual aninterface() {...} // , here };  class concrete : public abstractbase, public aninterface {}; 

my interface needs base class pointer concrete class inheriting in constructor , destructor in order handle interface related registration , deregistration.

every concrete object inherits interface needs inherit abstract base class first, first in layout.

for constructor not hard, can add pointer in interface constructor , pass this concrete class. destructor doesn't have parameters, in dark there.

the solutions came far come overhead:

1 - store pointer in interface used in destructor - adds in 1 pointer worth of memory overhead

class aninterface { public:     aninterface(abstractbase * ap) {...}     ~virtual aninterface() {...} // , here private:     abstractbase * aptr; };  ... concrete() : aninterface(this) {} 

2 - create abstract method in interface , implement return this in concrete class - adds in overhead of indirection virtual call

class aninterface {     virtual abstractbase * getptr() = 0; };  class concrete : public abstractbase, public aninterface {     abstractbase * getptr() { return this; } }; 

3 - dynamic_cast worse

is there more efficient way achieve this?

imo if decoupling between base class , interface needed, both solution 1 , 2 have tolerable overheads, nothing problem on contemporary hardware.

but since interface designed work functionality, provided in base class, maybe decoupling not thing.

i mean if problem inheriting multiple interfaces inherit base class, or "dreaded diamond" problem inheritance, can use virtual inheritance.