Question

我是面向对象编程的初学者。作为学习项目，我决定创建一个管理公司的小程序。如何计算创建的对象？我读过它但我不明白。我想要告诉我如何使用我的代码作为示例：

class Employee
{
public:
    std::string name;
    int age;
    static int id;

    Employee::Employee()
    {
        id++;
    }
};

int Employee::id = 0;

std::ostream& operator<<(std::ostream& out, const std::vector<Employee>& v)
{
    out << "[";
    for (size_t i = 0; i < v.size(); ++i)
    {
        out << "ID: " << v[i].id <<  " Name: " << v[i].name << " age: " << v[i].age;
        if (i != v.size() - 1)
            out << ", ";
    }
    out << "]";

    return out;
}

Employee generate_random_employee(Employee obj)
{
    std::vector<std::string> male_names = {"Donald", "Piotr", "James", "Tiny", "Ricky"};
    std::vector<std::string> female_names = {"Diana", "Joelle", "Sue", "Karolina"};
    std::vector<std::string> lastnames = {"Lester", "Pound", "Park", "Ennis", "Duck",
                                        "Tusk", "Disney", "Jurassic", "Looney-Warde" };

    int sex = (rand() % 2) + 0;

    if (sex == 1)
    {
        obj.name = male_names[(rand() % (male_names.size() - 1)) + 0];
    }
    else
    {
        obj.name = female_names[(rand() % (female_names.size() - 1)) + 0];
    }

    obj.name += " " + lastnames[(rand() % (lastnames.size() - 1)) + 0];
    obj.age = (rand() % 24) + 25;

    return obj;
}

int main()
{
    srand(time(NULL));

    std::vector<Employee> employees;
    Employee some_new_employee;

    for(int i = 0; i < 2; i++)
    {
        some_new_employee = generate_random_employee(some_new_employee); //randomly generate a new employee. It is Employee type function
        employees.push_back(some_new_employee);
    }

    std::cout << employees << std::endl;
}

目前程序经常将1作为所有对象的ID

Answer 1

要为每位员工获取唯一ID，请尝试：

class Employee
{
public:
   std::string name;
   int age;
   int id;

   static int ID;

   Employee()
      {
         id = ID++;
      }
};

int Employee::ID = 0;

std::ostream& operator<<(std::ostream& out, const std::vector<Employee>& v)
{
   // ...
   return out;
}

主要（简化）

   std::vector<Employee> employees;

   for(int i = 0; i < 4; i++)
   {
      Employee e;
      employees.push_back(e);
   }

   std::cout << employees << std::endl;

输出：

[ID: 0 Name:  age: 0, ID: 1 Name:  age: 0, ID: 2 Name:  age: 0, ID: 3 Name:  age: 0]

关键思想：对象的每个实例都需要一个唯一的 id。静态正好相反......所有实例的共同值。

ctor设置自己的id并增加静态ID。

请注意，ID表示已构建的数量，但不包含可能存在的数量（考虑析构函数，临时值，副本等）。

Answer 2

generate_random_employee(some_new_employee); employees.push_back(some_new_employee);

这些行都没有调用构造函数。

您应该重载赋值运算符或复制构造函数以增加计数。

并且您无法获得静态ID ...静态意味着您的所有实例都具有相同的ID ...

你想要一个satic计数器并用它来分配构造中的id。

如何自动将ID属性赋予c ++

2 个答案: