如何在 C++ 中输入对象？

Question

您好，下面的代码是一个简单的 C++ 类示例

#include <iostream>
using namespace std;

class Car {        // The class
  public:          // Access specifier
    string brand;  // Attribute
    string model;  // Attribute
    int year;      // Attribute
    Car(string x, string y, int z) {  // Constructor with parameters
      brand = x;
      model = y;
      year = z;
    }
};

int main() {
  // Create Car objects and call the constructor with different values
  Car carObj1("BMW", "X5", 1999);
  Car carObj2("Ford", "Mustang", 1969);

  // Print values
  cout << carObj1.brand << " " << carObj1.model << " " << carObj1.year << "\n";
  cout << carObj2.brand << " " << carObj2.model << " " << carObj2.year << "\n";
  return 0;
}
// W3Schools

在我看来，定义对象的方法是用如下代码编写它：<ClassName> <ObjectName>

现在我的问题是：有没有办法输入一个对象？喜欢cin >> ObjectName;

在我们输入对象名称后，我们输入参数。

有可能吗？

Answer 1

您不能从命令行输入对象名称，但是，您可以创建一个默认构造的对象，然后通过重载 operator>> 从输入中填充其属性。

class Car {
  public:
    Car() = default;
    // ...
};

std::istream& operator>>(std::istream& in, Car& car) {
  in >> car.brand >> car.model >> car.year;
  return in;
}

int main() {
  Car carObj1;
  cout << "Enter a car brand, model, and year: ";
  cin >> carObj1;
  // ...
}

Answer 2

是的，C++ 中有运算符重载，您可以重载 > 运算符。这是一个示例代码：

#include <iostream>
using namespace std;

class Car {        // The class
  public:          // Access specifier
    string brand;  // Attribute
    string model;  // Attribute
    int year;      // Attribute
    Car(string x, string y, int z) {  // Constructor with parameters
      brand = x;
      model = y;
      year = z;
    }

    Car() = default;

    void Carinput(std::istream& is)
    {
        is >> brand >> model >> year;
    }

    void carOutput(std::ostream& os) const
    {
        os << brand << " " << model << " " << year << std::endl;
    }
};

std::istream &operator>>(std::istream &is,Car &car)
{
    car.Carinput(is);
    return is;
}

std::ostream &operator<<(std::ostream &os,const Car &car)
{
    car.carOutput(os);
    return os;
}

int main() {
  // Create Car objects and call the constructor with different values
  Car carObj1("BMW", "X5", 1999);
  Car carObj2("Ford", "Mustang", 1969);

  // Print values
  cout << carObj1.brand << " " << carObj1.model << " " << carObj1.year << "\n";
  cout << carObj2.brand << " " << carObj2.model << " " << carObj2.year << "\n";

  std::cout << "\n*============================================*\n"
            << std::endl;

  std::cout << "Your input:" << std::endl;
  Car carObj3;
  std::cin >> carObj3;
  std::cout << carObj3;

  return 0;
}

Answer 3

这是其中一种方法：

#include<iostream>
#include<vector>


class Car
{
public:
    Car( const std::string& brand, const std::string& model, int year )
    : m_brand( brand ), m_model( model ), m_year( year ) // initialize members like this
    {
    }

    std::string m_brand;
    std::string m_model;
    int m_year;
};

int main ()
{
    std::vector< Car > cars; // use an std::vector to store the objects
    std::string brand( "" );
    std::string model( "" );
    std::string year( "" );
    

    std::cout << "How many cars do you want to add? ";
    std::string count( "" );
    std::getline( std::cin, count ); // get input as string using std::getline()
    int carCount { std::stoi( count ) }; // converts it to type int before 
                                         // assigning it to carCount

    cars.reserve( carCount ); // reserve some space in vector to avoid 
                              // unnecessary allocations and slowdowns

    for ( int idx = 0; idx < carCount; ++idx )
    {
        std::cout << "Enter the brand name of car number " << idx + 1 << ": ";
        std::getline( std::cin, brand );

        std::cout << "Enter the model name of car number " << idx + 1 << ": ";
        std::getline( std::cin, model );

        std::cout << "Enter the production year of car number " << idx + 1 << ": ";
        std::getline( std::cin, year );

        cars.emplace_back( Car( brand, model, std::stoi( year ) ) ); // push the new Car
    }                                                                // instance to the
                                                                     // vector called cars
    std::cout << '\n';

    for ( int idx = 0; idx < carCount; ++idx )
    {
        std::cout << "Info for car number " << idx + 1 << ": "
        << cars[ idx ].m_brand << " " << cars[ idx ].m_model << " " << cars[ idx ].m_year << "\n";
    }
    return 0;
}

这是输出：

How many cars do you want to add? 2
Enter the brand name of car number 1: Porsche
Enter the model name of car number 1: GT3 RS
Enter the production year of car number 1: 2019
Enter the brand name of car number 2: BMW
Enter the model name of car number 2: M6
Enter the production year of car number 2: 2016

Info for car number 1: Porsche GT3 RS 2019
Info for car number 2: BMW M6 2016

但是请记住，这个类仍然需要做很多工作，比如添加成员函数（如 getter 和 setter）等。所以这不是我编写类的方式。我只是想保持简单，以便您可以轻松理解这些概念。