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    if(c) {c->f2(); std::cout << "it executed" << std::endl;}
    else {std::cout << std::endl << " it isn't executed ";} // Не выполнено
}

C++ (Qt)
    if (c) {
       c->f2(); 
       std::cout << "it executed" << std::endl;
    }
    else 
       std::cout << std::endl << " it isn't executed "; // Не выполнено
 

C++ (Qt)
class B{
public:
    virtual void f1(){
        //
 
        qDebug() << "B";
    }
};
class C {
public:
    virtual void f2(){
        //
 
        qDebug() << "C";
    }
};
class D: public B, public C {};
 
void demo(B* b) {
    //
 
    C* c = dynamic_cast<C*>(b);
    if(c)
        c->f2();
}
 
int main(int argc, char *argv[]) {
    //
 
    QCoreApplication a(argc, argv);
 
    D* d = new D;
    demo(d);
    delete d;
 
    return a.exec();
}

(D*)b

C++ (Qt)
    D* d = new D;
}

C++ (Qt)
B * b = dynamic_cast <B *> (p);
C * c = dynamic_cast <C *> (b);

C++ (Qt)
#include <iostream>
#include <typeinfo>
 
class B {
    public: virtual void f1(){};
};
 
class C: public B{
    public: void f2(){ std::cout << "f2 is true"; };
};
 
class D: public B {
    public: void f3(){ std::cout << "f3 is true"; };
};
 
void demo( D * p )
{
//    C * c = dynamic_cast <C *> (p); 
    B * b = dynamic_cast <B *> (p); 
    C * c = dynamic_cast <C *> (b); 
    if (c) {
		c->f2(); 
		std::cout << "it executed" << std::endl;
	}
    else 
		std::cout << std::endl << " it isn't executed "; // Не выполнено
}
 
int main(int argc, char *argv[])
{
    B * b = new C;  
    demo((D*) b);   
    return 0;
}