<< Operator Rewrite to cout int and double values

问题

I need to rewrite the << operator so that it can cout values for hour (int) and temperature (double).

I think I've included all necessary sections. Thanks in advance.

struct Reading {
    int hour;
    double temperature;
    Reading(int h, double t): hour(h), temperature(t) { }
    bool operator<(const Reading &r) const;
};

========

ostream& operator<<(ostream& ost, const Reading &r)
{
    // unsure what to enter here

    return ost;
}

========

vector<Reading> get_temps()
{
// stub version                                                                 
    cout << "Please enter name of input file name: ";
    string name;
    cin >> name;
    ifstream ist(name.c_str());
    if(!ist) error("can't open input file ", name);

    vector<Reading> temps;
    int hour;
    double temperature;
    while (ist >> hour >> temperature){
        if (hour <0 || 23 <hour) error("hour out of range");
        temps.push_back( Reading(hour,temperature));
    }

}

回答1:

For example like this:

bool operator <(Reading const& left, Reading const& right)
{
    return left.temperature < right.temperature;
}

And it should be a global function (or in the same namespace as Reading), not a member or Reading, it should be declared as a friend if you going to have any protected or private members. This could be done like so:

struct Reading {
    int hour;
    double temperature;
    Reading(int h, double t): hour(h), temperature(t) { }

    friend bool operator <(Reading const& left, Reading const& right);
};

回答2:

You probably want something like

ost << r.hour << ' ' << r.temperature;

This is pretty simple stuff though, and if it doesn't make sense you should really talk to someone or get a book.

And if it still doesn't make sense or you can't be bothered, consider choosing another hobby/career.

回答3:

IIRC, you can do it one of two ways ...

// overload operator<
bool operator< ( const Reading & lhs, const Reading & rhs )
{
  return lhs.temperature < rhs.temperature;
}

or, you can add the operator to your struct ...

struct Reading {
  int hour;
  double temperature;
  Reading ( int h, double t ) : hour ( h ), temperature ( t ) { }
  bool operator< ( const Reading & other ) { return temperature < other.temperature; }
}

回答4:

Use ost parameter like std::cout in operator<<.

回答5:

r.hour()
r.temperature()

You've declared hour and temperature as member fields of Reading, not member methods. Thus they are simply r.hour and r.temperature (no ()).

回答6:

As hour and temperature are variables rather than functions, just remove the trailing () from the operator<< functions.

回答7:

You can overload an operator like this in c++.

struct Reading {
     int hour;
     double temperature;
     Reading(int h, double t): hour(h), temperature(t) { }
     bool operator<(struct Reading &other) {
         //do your comparisons between this and other and return a value
     }
}

来源：https://stackoverflow.com/questions/4362077/operator-rewrite-to-cout-int-and-double-values

标签

c++

iostream

ostream