为什么在 class 中没有对象就可以调用非静态方法？

Question

无论我在哪里搜索，我都发现要使用没有对象的方法，唯一的方法是将其设为静态。然而，在下面的代码中，我展示了两个在没有对象的情况下调用非静态方法的示例 FindIngredient 和 NumPizzas()((*) 和 (**))。它编译，甚至没有给出警告。如您所见，我没有在任何地方使用 static

怎么可能？

          class Ingredient {
    public:
      string Name;
      int Price;
      string Description;};

      class Pizza {
          vector<Ingredient> ingredients;
        public:
          string Name; 
          void AddIngredient(const Ingredient& ingredient){ingredients.push_back(ingredient);}
      };


    class Pizzeria {
        map<string, Ingredient> mapNameToIngredient;
        map<string, Pizza> mapNameToPizza;
        
        void AddPizza(const string &name, const vector<string> &ingredients)
            {
                if(mapNameToPizza.find(name) != mapNameToPizza.end())
                {
                    throw runtime_error("Pizza already inserted");
                }
                else
                {
                    Pizza pizza;
                    pizza.Name = name;
                    for(size_t i = 0;  i < ingredients.size(); i++)
                     {
                         Ingredient ingredient= FindIngredient(ingredients[i]); //(*)
                         pizza.AddIngredient(ingredient);
                      }
                    mapNameToPizza[name] = pizza;
                }
            }
        
            void AddIngredient(const string &name, const string &description, const int &price)
                {
                    if(mapNameToIngredient.find(name) != mapNameToIngredient.end())
                    {
                       throw runtime_error("Ingredient already inserted");
                    }
                    else
                    {
                       Ingredient ingredient;
                       ingredient.Name = name;
                       ingredient.Price = price;
                       ingredient.Description = description;                  
                       mapNameToIngredient[name] = ingredient;
                    }
                }
    const Ingredient &FindIngredient(const string &name) const
    {
        auto it = mapNameToIngredient.find(name);
        if(it != mapNameToIngredient.end())
        {
           return it->second;
        }
        else
        {
           throw runtime_error("Ingredient not found");
        }
    }
    };
class Order {
      vector<Pizza> pizzas; 
    public:
      int numOrder;

      int NumPizzas() const { return pizzas.size(); }
      int ComputeTotal() const;
        {
            int total = 0;
            for(size_t i = 0; i < (size_t)NumPizzas(); i++) //(**) why is it letting me use the method as a static function?
            {
                total += pizzas[i].ComputePrice();
            }
            return total;
        } 
 };

Answer 1

当您从另一个成员函数调用一个成员函数时，该对象是隐含的 - 它是 this->。

为什么在 class 中没有对象就可以调用非静态方法？

How come non-static methods can be called without an object inside the class?

c++

oop

methods

static-methods