Example

class Base {
public:
void fnc();
};

class Derived: public Base {
public:
void fnc(){}
};

void callDerivedFunction(Base *ptr){

Derived *dp = (Derived*) ptr;
dp->fnc();

}

Solution

Do not cast a pointer of one class to the a pointer of a class it does not inherit from. To avoid errors, do not use pointers for down casting. Use virtual functions instead.

class Base {
public:
virtual void fnc();
};

class Derived: public Base {
public:
virtual void fnc(){}
};

void callDerivedFunction(Base *ptr){

ptr->fnc();

}