How to implement Inheritance in C++ and resolve the error “parent class is not accessible base of child class”?

Question

I am new to C++. I like to explore the idea of Inheritance in C++. Whenever I try to compile the following code I get the error:

for C++ includes, or <iostream> instead of the deprecated header <iostream.h>. To disable this warning use -Wno-deprecated.
D:\C Practice Files\Vehicle.cpp: In function `int main()':
D:\C Practice Files\Vehicle.cpp:26: error: `void Vehicle::setStationary_state(bool)' is inaccessible
D:\C Practice Files\Vehicle.cpp:141: error: within this context
D:\C Practice Files\Vehicle.cpp:141: error: `Vehicle' is not an accessible base of `Ship'

Execution terminated

Here is my code:

 #include <iostream.h>
 #include <conio.h>
 using std::string;

 class Vehicle{

          private:           
               bool stationary_state;
               double max_speed;
               double min_speed;
               double weight;
               double volume;
               int expected_life;
               string fuel_type;
               string model;
               string year_of_manufacture;   

          public:        
               Vehicle(){
               }

               void setStationary_state(bool m){
                         stationary_state = m;                 
               }  

               bool getStationary_state(){
                         return stationary_state;                 
               }    
    };


    class Bike:Vehicle{
           private: 
               string bike_type;

           public:
               void setBike_Type(string t){
                    type = t;
               }      
               string getBike_Type(){
                    return bike_type;
               }
    };      


    class Aircraft:Vehicle{
          private:
             short no_of_wings;

          public:
             void setNo_of_wings(short wings)
             {

                 no_of_wings = wings; 
             }   

             short getNo_of_wings()
             {
                  return no_of_wings;      
             }
          };



    class Car:Vehicle{

          private: 
             string reg_no;
             string type;

          public:
             void setType(string t)
             {

               if ((t=="Pneumatic") || (t=="Hydraulic"))
               {   
                  type = t;
               }
               else
               {
                  cout<<"\nInvalid entry. Please enter the correct type:";
                  setType(t);        
               }
             }    
          };




    class Ship:Vehicle{

          private:
             bool has_radar_detection;  


          public:
             void setRadar_Detection(bool r){

                  has_radar_detection = r;                                           
             }

             bool getRadar_Detection(){
                  return has_radar_detection;                                 
             }    

          };


        int x;  
    main()
    {
      Vehicle v;

      Bike b;

      Car c;

      Aircraft a;

      Ship s;

      s.setStationary_state(true);

      c.setType("xyz");



      /*v.setStationary_state(true);  

      if (!(v.getStationary_state()))
      {
         cout<<"Vehicle is moving";                        
      }
      else 
      {
         cout<<"Vehicle is at rest";  
      }        
      */

      getch();    
    }

What is really wrong there? What is the cause of the error and how to avoid it. Please explain in detail.

Answer 1

class has private default inheritance, so you would need to specify public , ie

class Ship : public Vehicle { }:

ans so on. struct has public inheritance as default.

Answer 2

You need to specify inheritance access level:

class Bike : public Vehicle

Ie you need to make Vehicle a public base.

Answer 3

If you don't specify an access specifier, inheritance is automatically private . You need to change these line:

 class Ship:Vehicle

to this:

 class Ship:public Vehicle

Answer 4

encapsulation is attained by placing related data in the same place and offering security to the data.include

1. private - access granted to same class
2. public - any code can access the data
3. protected - access granted to methods of the same class,friend class and derived class