如何使用运算符打印类对象<<

Question

我想为 AutoData 类编写一个打印函数，其中包含有关汽车的信息。通过这个打印函数，我理想地希望打印出包含许多不同类对象的向量。我已经为对象的每个元素编写了 get 函数，但我仍然有点不确定如何使用这些函数来编写函数以以下格式打印数据：

mpg:cylinders:displacement:horsepower:weight:acceleration:modelYear:origin:carName

例如：

10.0:8:360.0:215.0:4615.:14.0:70:1:ford f250
10.0:8:307.0:200.0:4376.:15.0:70:1:chevy c20
11.0:8:318.0:210.0:4382.:13.5:70:1:dodge d200

班级是：

#include <string>
#include <vector>
#include <iostream>

using namespace std;

class AutoData {

public:
    AutoData()
    {
        mpg = 0;
        cylinders = 0;
        displacement = 0;
        horsepower = 0;
        weight = 0;
        acceleration = 0;
        modelYear = 0;
        origin = 0;
        carName = "";
    }

    AutoData( const AutoData & rhs)
    {
        setAuto(rhs.mpg, rhs.cylinders, rhs.displacement, rhs.horsepower, rhs.weight, rhs.acceleration, rhs.modelYear, rhs.origin, rhs.carName);
    }

    void setAuto(float mp, int cy, float di, float ho, float we, float ac, int mo, int o, string ca)
    {
        mpg = mp;
        cylinders = cy;
        displacement = di;
        horsepower = ho;
        weight = we;
        acceleration = ac;
        modelYear = mo;
        origin = o;
        carName = ca;
    }

    const float & getmpg( ) const
    {
        return mpg;
    }

    const int & getcylinders( ) const
    {
        return cylinders;
    }

    const float & getdisplacement( ) const
    {
        return displacement;
    }

    const float & gethorsepower( ) const
    {
        return horsepower;
    }

    const float & getweight( ) const
    {
        return weight;
    }

    const float & getacceleration( ) const
    {
        return acceleration;
    }

    const int & getmodelYear( ) const
    {
        return modelYear;
    }

    const int & getorigin( ) const
    {
        return origin;
    }

    const string & getcarName( ) const
    {
        return carName;
    }

    bool operator == (const AutoData & rhs ) const
    {
        if( getmpg( ) == rhs.getmpg( ) )
        {
            return gethorsepower( ) == rhs.gethorsepower( );
        }

        else
        {
            return false;
        }
    }

    bool operator > ( const AutoData & rhs ) const
    {
        if( rhs.getmpg( ) > getmpg( ) )
        {
            return true;
        }

        else if( getmpg( ) == rhs.getmpg( ) )
        {
            if( rhs.gethorsepower( ) > gethorsepower( ) )
            {
                return true;
            }
        }

        else
        {
            return false;
        }
    }


private:
    float mpg;
    int cylinders;
    float displacement;
    float horsepower;
    float weight;
    float acceleration;
    int modelYear;
    int origin;
    string carName;
};

任何人可以提供的任何帮助/建议将非常感激！谢谢

Answer 1

如果你想能够做到

std::cout << AutoData();

，你需要重载输出流运算符

operator<<

：

std::ostream& operator<<(std::ostream &out, AutoData const& data) {
    out << data.getmpg() << ':';
    out << data.getcylinders() << ':';
    // and so on... 
    return out;
}

此函数不是成员函数，并且由于每个属性都有 getter，因此您不必将此函数声明为类的

friend

。

然后你可以这样做：

AutoData myAuto;
std::cout << myAuto << '\n';

Answer 2

到目前为止您尝试过什么？我的方法是超载

operator<<

，例如：

std::ostream& operator<<(std::ostream& out, const AutoData& dasAuto) {
  return out << dasAuto.getmpg() << ':' << dasAuto.getcylinders() <<
    /* insert everthing in the desired order here */
    std::endl;
}

“阅读”功能也是如此，例如：

std::istream& operator>>(std::istream& in, AutoData& dasAuto) {
  float mpg;
  int cylinders;
  float displacement;
  float horsepower;
  float weight;
  float acceleration;
  int modelYear;
  int origin;
  string carName;
  char separator;
  const char SEP = ':';

  if( !(in >> mpg >> separator) || (separator != SEP) ) return in;
  if( !(in >> cylinders >> separator) || (separator != SEP) ) return in;
    /* rinse, repeat */
  if( !std::getline(in, carName) ) return in;
  dasAuto.setAuto(mpg, cylinders /*, etc etc */);
  return in;
}

Answer 3

您可以阅读这篇文章来了解

friend

和

operator <<

， http://www.cprogramming.com/tutorial/friends.html

在类

AutoData

中，你应该声明这个函数：

friend ostream& operator<< (ostream& out, const AutoData& obj); 

在类之外，你应该像这样定义这个函数：

ostream& operator<< (ostream& out, const AutoData& obj)
{
    out<<obj.mpg<<":";
        //do what you want
    return out;
}