- A child (sub) class
and
the parent (super) class
are
distinct (differnt) classes
- Therefore, from the
access qualifiers' rules
(see click here):
- The child (sub) class can access the public variables in the parent (super) class
- The child (sub) class
can NOT access the
private variables in
the parent (super) class
- The parent (super) class can access the public variables in the child (sub) class
- The parent (super) class can NOT access the private variables in the child (sub) class
- Example:
class parent { public: int i1; void f1() { cout << "public parent method" << endl; } private: int i2; void f2() { cout << "private parent method" << endl; } }; class child : public parent { public: void worker() { i1 = 1; // Allowed f1(); i2 = 1; // Forbidden... f2(); } };
- Example Program:
(Demo above code)
- Prog file: click here
- There is a
special relationship
between the
child class
and its
parent class -
it "inherits" all the
variables and functions in
the
parent class
So there is an access qualifier to allow only methods in the child class to access the variables in the parent class
This access qualifier is:
protected
- Example:
class parent { protected: int i2; void f2() { cout << "protected parent method" << endl; } }; class child : public parent { public: void worker() { i2 = 1; // Child class can access protected members // in parent class f2(); } }; int main(int argc, char **argv) { child x; parent y; x.worker(); y.f2(); // Forbidded... }
- Example Program:
(Demo above code)
- Prog file: click here
- There are 3 types
of
inheritances
in C++
- public
class C : public base_class { ... }When a base class is specified as public, then the base class can be "seen" by any part of the program that has access to the derived class.
- private
class C : private base_class { ... }When a base class is specified as private, then the base class can only be "seen" by the class C itself
- protected
class C : protected base_class { ... }When a base class is specified as protected, then the base class can only be "seen" by the class C and its subclasses
- public