Doesn't the public access specifier already allow derived classes?

Question

I don't see the point of the protect access specifiers when public does the same thing.

Answer 1

public access specifiers allows access to the members not only from derived classes but also from outside of the class.
protected access specifers allows access from only the same and derived classes. You can't access to protected members outside of a class.

for example, it is not good if a user of your class will change some internal state of the object, so declare setStatus as protected:

class A{
protected:
void setStatus(int status); // accessible, ok derived class can change it

public:
int getStatus();
};

class B: public A{
public:
B(){
setStatus(Initialized);
}
};

//.... somewhere in code:

B b;

b.setStatus(SignedIn); //will not compile as setStatus is protected

auto ststus2 = b.getStatus(); //will compile

Answer 2

You cannot access protected member out of the class while you can do it with public member.