How to construct a class with user inputs and no variables?

Question

One of my assignments involve creating a class using a constructor with parameters, where the arguments sent to create the object are based on user input.

#include <iostream>
#include "HRCalc_lib.h"

HeartRates::HeartRates(const std::string &first, const std::string &last, 
        int day, int month, int year){
    firstName = first;
    lastName = last;
    setBirthYear(year);
    setBirthMonth(month);
    setBirthDay(day);
}

Note: This is from a .cpp file where member functions are fully written. All other class syntax is in a header file.

I approached creating an object with this constructor using std::cin with variables through main.

#include <iostream>
#include "HRCalc_lib.h"

int main(){
    std::string first, last;
    int Bday, Bmonth, Byear;
    std::cout << "enter your name (first last) & date of birth (dd mm yyyy) seperated by spaces" << std::endl;
    std::cin >> first >> last >> Bday >> Bmonth >> Byear;

    HeartRates person1(first, last, Bday, Bmonth, Byear);

//further code would be implemented here
    return 0;
}

Is there a more direct way of creating the same object without the need for variables in main?

@NicolBolas Perhaps I should clarify a bit, I'm not seeking any further use for these variables so storing them would be pointless. I'm simply looking to create a class with user input as means to send arguments to my constructor function — Goroz
– Goroz, Commented Mar 5, 2022 at 4:07
You could move them into place but other than that there isn’t much more you can do here — Taekahn
– Taekahn, Commented Mar 5, 2022 at 4:10
@Goroz You can use operator overloading as shown in my answer below. — Richard
– Richard, Commented Mar 5, 2022 at 8:27

Richard · Accepted Answer · 2022-03-05 08:28:52Z

2

Is there a more direct way of creating the same object without the need for variables to store user inputs in main?

Yes, there is. You can use operator overloading. In particular, you can overload operator>> as shown below:

#include <iostream>
#include<string>

class HeartRates
{
   private:
      std::string first, last;
      int day = 0, month = 0, year = 0;
   //friend declaration for overloaded operator>>
   friend std::istream& operator>>(std::istream& is, HeartRates& obj);
};
//implement overloaded operator<<
std::istream& operator>>(std::istream& is, HeartRates& obj)
{
    is >> obj.first >> obj.last >> obj.day >> obj.month >> obj.year;
    
    if(is)//check that input succeded
    {
        //do something here 
    }
    else //input failed: give the object a default state
    {
        
        obj = HeartRates();
    }
    return is;
}
int main(){
    
    HeartRates person1;
    //NO NEED TO CREATE SEPARATE VARIABLES HERE AS YOU WANT
    
    std::cout << "enter your name (first last) & date of birth (dd mm yyyy) seperated by spaces" << std::endl;
    std::cin >> person1; //this uses overloaded operator>>

    return 0;
}

The output of the above program can be seen here.

Here when we wrote:

std::cin >> person1;

we're using the overloaded operator>> and so you don't need to create separate variables inside main.

edited Mar 5, 2022 at 8:28

answered Mar 5, 2022 at 4:18

Richard

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2 Comments

Goroz Over a year ago

Are the if statements there in case of invalid user input (Exception code basically) or is there a more blatant reason? Is there some obvious error input to consider when implementing overloads? I'm asking because I have user input checks already in my program.

Richard Over a year ago

@Goroz Yes the if/else inside the overloaded operator>> is there to deal with invalid input. It is good practice to leave the object in a default state in case the user enters invalid data.

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