How overload operator < for sort method for objects?

Question

I have this object, for example

 class Employee{
    int id;
    string name;
    string secName;
    }

My main is :

int main(){
vector<Employee> vec = {Employee(1, "Andy", "Good"), Employee(5, "Adam", "Bad"), Employee(2, "Some", "Employee")}

sort(vec.begin(), vec.end())

}

I know how overload sort method for vector when I have one parameter for sorting. It's like:

 bool operator<(Employee a, Employee b ){
    if (a.name<b.name) return true;
    else return false;
    }

But the point is that I have sort not only on one parameter, but on all. So how should I change overloading method?

I've tried this way, but it doesn't work.

bool operator<(Employee a, Employee b)
{
    if (a.id < b.id)
        if (a.name < b.name)
            if (a.surname<b.surname)return true; else return false;
        else return false;
    else return false;
}

The parameters are a and b, which you both include in the sorting process, so what do you mean "[...] but on all."? The members of the Employee objects? — cadaniluk
– cadaniluk, Commented Mar 17, 2016 at 9:31
Yes, I want sort vector considering not only name field, but also id, and secName. Maybe my English is not very good. — Azula
– Azula, Commented Mar 17, 2016 at 9:33
Then just include them in your operator< function and write appropriate if-clauses. The exact code depends on how you want to sort the Employees in particular, so that's up to you. — cadaniluk
– cadaniluk, Commented Mar 17, 2016 at 9:34
I don't know right way to do this. I've tried, but it not sorts appropriate. — Azula
– Azula, Commented Mar 17, 2016 at 9:36

Scintillo · Accepted Answer · 2016-03-17 09:44:55Z

4

If you want to sort primarily by id, secondarily by name and tertiary by secName this should work:

bool operator<(Employee a, Employee b)
{
    if (a.id < b.id) return true;
    if (a.id > b.id) return false;
    if (a.name < b.name) return true;
    if (a.name > b.name) return false;
    if (a.secName < b.secName) return true;
    return false;
}

answered Mar 17, 2016 at 9:44

Scintillo

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1 Comment

Azula Over a year ago

Yes. It is exactly what I've wanted. Thanks)

RyanCu · Accepted Answer · 2018-11-02 07:53:11Z

2

If you want to sort primarily by id, secondarily by name and tertiarily by secName, you could use this trick involving std::tie:

#include <tuple>

// ...

bool operator<(const Employee& lhs, const Employee& rhs)
{
    return std::tie(lhs.id, lhs.name, lhs.secName)
         < std::tie(rhs.id, rhs.name, rhs.secName);
}

It's also best for the function parameters to be passed in as const-refs (const &).

answered Nov 2, 2018 at 7:53

RyanCu

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