CODEWITHSUNDEEP
c++classmethodspropertiesthis
Adam Halasz
Adam Halasz

Reputation: 58341

C++: How to get a private property with a dynamic variable in a class?

I would like to create a simple Car class that has a Car::get method that I can use to access private properties of the car with a string such as:

// Create Car Intance
Car myCar;
cout << myCar.get("wheels");

My problem is that I don't know how to point the private property with a dynamic variable. Here is the class:

// Libraries & Config
#include <iostream>
using namespace std;

// Create Car Class
class Car {
   private: 
       int wheels = 4;
       int doors = 5;
   public: 
       Car();                // constructor
       ~Car();               // deconstructor
       int get(string what); //
};

// Constructor
Car::Car(){ cout << "Car constructed." << endl; }

// Deconstructor
Car::~Car(){ cout << "Car deconstructed." << endl; }

// Get Method
int Car::get(string what){
    // === THE PROBLEM ===
    // How do I access the `wheels` property of the car class with the what argument?
    return this[what] // ??
}

// Create Car Instance
Car myCar;
cout << myCar.get("wheels");

Upvotes: 1

Views: 919

Answers (2)

Galik
Galik

Reputation: 48645

You can do something like this using a std::map:

#include <map>
#include <string>
#include <iostream>

using namespace std;

class Car {
   private:
       std::map<std::string, int> parts = {{"wheels", 4}, {"doors", 5}};

   public:
       Car();
       ~Car();
       int get(std::string what);
};

// Constructor
Car::Car(){ std::cout << "Car constructed." << endl; }

// Deconstructor
Car::~Car(){ std::cout << "Car deconstructed." << endl; }

// Get Method
int Car::get(string what){

    return parts[what];
}

int main()
{
    // Create Car Intance
    Car myCar;
    cout << myCar.get("wheels") << '\n';
}

It is worth reading up on exactly how a std::map works here: http://en.cppreference.com/w/cpp/container/map

Upvotes: 2

ravi
ravi

Reputation: 10733

class Car {
   private: 
       int wheels = 4;    <<< This would flag an error as you cannot provide
       int doors = 5;     <<< in class initialization for non-consts.


int Car::get (string what)
{
  if( what == "wheels" )        //// check for case sensitivity...
      return wheels;
  else
      return doors;
}

Upvotes: 1

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