C++：如何在类中获取带有动态变量的私有属性？

Question

我想创建一个简单的 Car class，它有一个 Car::get 方法，我可以使用该方法通过以下字符串访问汽车的私有属性：

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

我的问题是我不知道如何用动态变量指向私有属性。这是 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");

Answer 1

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;
}

Answer 2

您可以使用 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';
}

std::map 的工作原理值得一读：http://en.cppreference.com/w/cpp/container/map

C++：如何在类中获取带有动态变量的私有属性？

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