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class BaseInterface {
    public:
        virtual void someMethod()=0;
};
 
class Derived: public BaseInterface {
    public:
        virtual void someMethod1()=0;
        void someMethod()override;
};
 
class ThirdClass {
    public:
        void demoMethod(BaseInterface&);
        void anotherMethod(Derived&);
};
 
void ThirdClass::demoMethod(BaseInterface& obj) {
    auto buffer=dynamic_cast<Derived&>(obj);
    anotherMethod(buffer);
}
 
int main() {}

prog.cpp: In member function 'void ThirdClass::demoMethod(BaseInterface&)':
prog.cpp:19:43: error: cannot allocate an object of abstract type 'Derived'
     auto buffer=dynamic_cast<Derived&>(obj);
                                           ^
prog.cpp:6:7: note:   because the following virtual functions are pure within 'Derived':
 class Derived: public BaseInterface {
       ^
prog.cpp:8:22: note: 	virtual void Derived::someMethod1()
         virtual void someMethod1()=0;
                      ^
prog.cpp:19:10: error: cannot declare variable 'buffer' to be of abstract type 'Derived'
     auto buffer=dynamic_cast<Derived&>(obj);
          ^

Standard output is empty