How to sort class objects array using the sort() in C++

Question

I was doing one programming problem where it is required to sort the class objects.

So, i used sort() to sort the array of objects but i couldn't do it, i read somewhere it requires lambda expression to that, but i don't know about them yet.

So, if you can help me with this question with some explanation of lambda expression it would be wonderful.

#include<bits/stdc++.h>
using namespace std;

class CallLog{
    public:
    string pno;
    int dur;
    string da;
    void setpno(string p_no) {pno = p_no;}
    void setdur(int d) {dur = d;}
    void setda(string dsa) {da = dsa;}
    string getpno() {return pno;}
    int getdur() {return dur;}
    string getda() {return da;}
};

int main() {
    int n;
    cin >> n;
    CallLog arr[n];
    for(int i = 0; i < n; i++) {
        string pno;
        int dur;
        string da;
        cin >> pno >> dur >> da;
        arr[i].setpno(pno);
        arr[i].setdur(dur);
        arr[i].setda(da);
    }
    sort(arr, arr+n, "what labmda expression to write?" );
    for(int i = 0; i < n; i++) {
        cout << "DialledNumber : " << arr[i].getpno() << ", Duration : " << arr[i].getdur() << ", Date : " << arr[i].getda() << "\n";
    }
}

I want to sort these objects with respect to the int dur.

ProTip: The variable-length arrays (VLAs) are not supported in C++. Therefore, statements like cin >> n; CallLog arr[n]; – is invalid. Instead, use a std::vector or dynamic memory allocation with new and delete pair. — Rohan Bari
– Rohan Bari, Commented Feb 25, 2021 at 16:41

Remy Lebeau · Accepted Answer · 2021-02-25 20:51:35Z

1

Sorting is about comparing elements and knowing which one is "lower" than other one (ie, if I sort {5,3,1} into {1,3,5}, it is because 1 is lower than 3 and 3 is lower than 5)

So, it depends on what kind of logic you want to follow for your sorting algorithm (you could, for example, sort them by their member int dur). sort() uses the < operator to sort, so you have two options:

Overload the < operator as shown here <= I suggest you to do this, for example:

bool operator<(CallLog a, CallLog b)
{
    return a.dur < b.dur;
}

You can actually use a lambda, as in this example <= notice that even if it shows how to do it using lambdas, it also shows that writing the < operator would be way nicer. Also here, there's an easy-to-read example on how to sort passing a function to sort().

edited Feb 25, 2021 at 20:51

Remy Lebeau

609k36 gold badges516 silver badges875 bronze badges

answered Feb 25, 2021 at 16:46

Ivan

1,5512 gold badges20 silver badges42 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Ivan Over a year ago

Note that as mentioned by Rohan Bari , using std::vector is the way

Alex Ed Over a year ago

Thanks for the insights

Alex Ed Over a year ago

thank you sir, it was finally working as desired!

Remy Lebeau Over a year ago

The overloaded operator< should take its parameters by const reference, not by value: bool operator<(const CallLog &a, const CallLog &b) You can alternatively implement the operator as a member of CallLog, eg: class CallLog { public: ... bool operator<(const CallLog &rhs) const { return dur < rhs.dur; } };

dilem-ma-vi · Accepted Answer · 2021-02-25 22:15:52Z

0

The predefined STL function objects, located in the FUNCTIONAL header file. There are function objects corresponding to all the major C++ operators. In the table, the letter T indicates any class, either user-written or a basic type. The variables x and y represent objects of class T passed to the function object as arguments. "bool = greater(T, T) x > y bool = less(T, T) x < y". Also if you want you can write your own function objects.

answered Feb 25, 2021 at 22:15

dilem-ma-vi

338 bronze badges

Collectives™ on Stack Overflow

How to sort class objects array using the sort() in C++

2 Answers 2

4 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related