<< Operator Rewrite to cout int and double values

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;
}

========开发者_StackOverflow中文版

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));
    }

}

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);
};

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.

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; }
}

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

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 ()).

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

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
     }
}