inheritance - C++: Declaring pointer to base and derived classes -

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i found confused 1 basic question in c++

class base {  };  class derived : public base {  }  base *ptr = new derived();

what mean? ptr pointing base class or derived class? @ line, how many memory allocated ptr? based on size of derived or base?

what's difference between , follows:

base *ptr = new base(); derived *ptr = new derived();

is there case this?

derived *ptr = new base();

thanks!

to understand type system of c++, important understand difference between static types , dynamic types. in example, defined types base , derived , variable ptr has static type of base *.

now when call new derived(), pointer static , dynamic type of derived *. since derived subtype of base can implicitly converted static type of base * , assigned ptr static types match. dynamic type remains derived * however, important if call virtual function of base via ptr, calling virtual functions based on dynamic type of object, not static type.


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