Using the private base class member variables with public class inheritance C++ program example
Compiler: Visual C++ Express Edition 2005
Compiled on Platform: Windows XP Pro SP2
Header file: Standard
Additional library: none/default
Additional project setting: Set project to be compiled as C++
Project -> your_project_name Properties -> Configuration Properties -> C/C++ -> Advanced -> Compiled As: Compiled as C++ Code (/TP)
Other info: none
To do: Removing the protected keyword of the base class member variable (become private) and using the public class inheritance for the derived class in C++ programming
To show: How to use the private base class member variable and the public class inheritance for the derived class in C++ programming
// using the C++ private base class member variables and public class inheritance
#include <iostream>
using namespace std;
// base and derived class declaration
// vehicle base class
class vehicle
{
// protected:
// note this is removed, so it is private now
int wheels;
double weight;
public: // public specifier
void initialize(int input_wheels, double input_weight);
int get_wheels(void) {return wheels;}
double get_weight(void) {return weight;}
double wheel_load(void) {return (weight/wheels);}
};
// car derived class with public inheritance
class car :public vehicle
{
int passenger_load;
public:
void initialize(int input_wheels,double input_weight, int people = 4);
int passengers(void) {return passenger_load;}
};
// truck derived class with public inheritance
class truck :public vehicle
{
int passenger_load;
double payload;
public:
void init_truck(int how_many = 4, double max_load = 24000.0);
double efficiency(void);
int passengers(void) {return passenger_load;}
};
// main program
int main(void)
{
vehicle unicycle;
unicycle.initialize(1, 12.5);
cout<<"Using the vehicle base class"<<endl;
cout<<"----------------------------"<<endl;
cout<<"The unicycle has "<<unicycle.get_wheels()<<" wheel."<<endl;
cout<<"The unicycle's wheel load is "<<unicycle.wheel_load()<<" kg on the single tyre."<<endl;
cout<<"The unicycle's weight "<<unicycle.get_weight()<<" kg."<<endl<<endl;
car sedan_car;
sedan_car.initialize(4, 3500.0, 5);
cout<<"Using car derived class with public inheritance"<<endl;
cout<<"-----------------------------------------------"<<endl;
cout<<"The sedan car carries "<<sedan_car.passengers()<<" passengers."<<endl;
cout<<"The sedan car's weight "<<sedan_car.get_weight()<< " kg."<<endl;
cout<<"The sedan car's wheel loading is "<<sedan_car.wheel_load()<<" kg per tyre."<<endl<<endl;
truck trailer;
trailer.initialize(18, 12500.0);
trailer.init_truck(1, 33675.0);
cout<<"Using truck derived class with public inheritance"<<endl;
cout<<"-------------------------------------------------"<<endl;
cout<<"The trailer's weight "<<trailer.get_weight()<<" kg."<<endl;
cout<<"The trailer's efficiency is "<<100.0 * trailer.efficiency()<<" %."<<endl;
return 0;
}
// base and derived class implementation part
// initialize to any desired data, this method own by base class
void vehicle::initialize(int input_wheels, double input_weight)
{
wheels = input_wheels;
weight = input_weight;
}
// this method own by derived class
void car::initialize(int input_wheels, double input_weight,int people)
{
passenger_load = people;
// this variable are invalid anymore because both wheels and weight are private now.
// wheels = input_wheels;
// weight = input_weight;
// an added statement, using base class method instead of derived class
vehicle::initialize(input_wheels, input_weight);
}
void truck::init_truck(int how_many, double max_load)
{
passenger_load = how_many;
payload = max_load;
}
double truck::efficiency(void)
{
// changed from the previous example, from weight() to get_weight()
return payload / (payload + get_weight());
}
Output example:
Using the vehicle base class
----------------------------
The unicycle has 1 wheel.
The unicycle's wheel load is 12.5 kg on the single tyre.
The unicycle's weight 12.5 kg.
Using car derived class with public inheritance
-----------------------------------------------
The sedan car carries 5 passengers.
The sedan car's weight 3500 kg.
The sedan car's wheel loading is 875 kg per tyre.
Using truck derived class with public inheritance
-------------------------------------------------
The trailer's weight 12500 kg.
The trailer's efficiency is 72.9291 %.
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