Sorting vector of objects c++ raise C2280 error

Question

I have a vector of Workout objects, and I want to sort it by the prices of the workout (each Workout have const field price and getPrice function) When Im trying to sort the array i get a C2280 error - Workout &Workout::operator =(const Workout &)': attempting to reference a deleted function

#ifndef WORKOUT_H_
#define WORKOUT_H_

#include <string>


class Workout {
public:
    Workout(int w_id, std::string w_name, int w_price, WorkoutType w_type);
    int getPrice() const;
    Workout& operator =(const Workout& other)
        {
            if (this == &other) return *this;
            return *new(this) Workout(other.getId(), other.getName(), 
            other.getPrice(), other.getType());
        }

private:
    const int price;
};

I else have virtual class Customer and cheapCustomer object that inheritence from it, and function- order(const std::vector& workout_options) that needs to sort the vector by the prices.

Here is the Customer cpp file -

#include "Customer.h"
#include <algorithm>
using namespace std;

Customer::Customer(std::string c_name, int c_id) :name(c_name), id(c_id)
{
}

CheapCustomer::CheapCustomer(std::string name, int id) :Customer(name, id)
{
}

std::vector<int> CheapCustomer::order(const std::vector<Workout>& workout_options)

{
    std::vector<int>* v = new std::vector<int>();
    std::vector<Workout> tmp = workout_options;
    std::sort(tmp.begin(), tmp.end(), [](const Workout& w1, const Workout& w2) {
        return w1.getPrice() < w2.getPrice();
        });
    return *v;
    //delete v


}


#include <vector>
#include "Customer.h"
#include "Trainer.h"
#include <algorithm>

using namespace std;
int main(int argc, char** argv) {
   
    Workout w1 = Workout(1, "w1", 10, CARDIO);
    Workout w2 = Workout(2, "w2", 20, CARDIO);
    Workout w3 = Workout(3, "w3", 30, MIXED)
    std::vector<Workout> v;
    v.push_back(w1);
    v.push_back(w2);
    v.push_back(w3);
    
    Customer* c_cheap = new CheapCustomer("Cheap", 20);
    vector<int> order_cheap = c_cheap->order(v);

can some one please tell me how to fix it? Thank you so much

I tried to use unique_ptr and still the same error-

C2280 'std::unique_ptr<Workout,std::default_delete>::unique_ptr(const std::unique_ptr<Workout,std::default_delete> &)': attempting to reference a deleted function

std::vector<int> CheapCustomer::order(const std::vector<Workout>& workout_options)

{
    vector<int>* v = new std::vector<int>();
    vector<unique_ptr<Workout>> v_unique_ptr;
    for (Workout workout : workout_options) {
        v_unique_ptr.push_back(unique_ptr<Workout>(new Workout(workout.getId(),workout.getName(),workout.getPrice(),workout.getType())));
    }
    std::sort(v_unique_ptr.begin(), v_unique_ptr.end(), [](unique_ptr<Workout> w1, unique_ptr<Workout> w2) {
        return w1->getPrice() < w2->getPrice();
        });
}

Edited: its worked here

    vector<int>* v = new std::vector<int>();
    vector<unique_ptr<Workout>> v_unique_ptr;
    for (Workout workout : workout_options) {
        v_unique_ptr.push_back(move(unique_ptr<Workout>(new Workout(workout.getId(),workout.getName(),workout.getPrice(),workout.getType()))));
    }
    std::sort(v_unique_ptr.begin(), v_unique_ptr.end(), [](unique_ptr<Workout>& w1, unique_ptr<Workout>& w2) {
        return w1->getPrice() < w2->getPrice();
        });
    v->push_back(v_unique_ptr[0]->getId());
    return *v;

Thank you so much

Please always (**ALWAYS**) copy and paste the entire unedited error message. Also. `new std::vector()` is wrong, don't do that. You should almost never use `new` in C++. You need to return a vector, so declare, use a return a vector, not a pointer. — n. m. could be an AI, Nov 13 '21 at 11:00
Not the error, but you are just sorting the `tmp` vector, then do nothing with it and return an empty vector from the method, i dont think this is what you wanted — Exagon, Nov 13 '21 at 11:22
Yes I know , I have more code on that block but its not relevant to my problem :) — Tal Alter, Nov 13 '21 at 11:54

n. m. could be an AI · Answer 1 · 2021-11-13T19:28:40.253

0

In order to use std::sort, the element type needs to be move-assignable. Your element type isn't, because of all the const data members.

So you may either:

Remove the const
Provide your own move assignment operator that somehow gets around const
Don't place Workout objects in a container, place pointers instead (preferably smart pointers such as unique_ptr).

edited Nov 13 '21 at 19:28

answered Nov 13 '21 at 12:07

n. m. could be an AI

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I tried to move the const from the variables inside the lambda function, and I cant make a move assigment operator because the fields inside Workout are consts and I cant change it. Maybe you have another idea? – Tal Alter Nov 13 '21 at 14:50
You can use the destroy-and-construct method of assignment e.g. https://stackoverflow.com/questions/11601998/assignment-of-class-with-const-member – n. m. could be an AI Nov 13 '21 at 17:06
Ok so I implemented move constructor and assigment constructor and I still get the same error. Please maybe some one have another idea? – Tal Alter Nov 13 '21 at 18:39
Please make sure to provide a [mcve] (pay attention to both minimal and reproducible parts). I think it's best to ask a new question, but whatever works. – n. m. could be an AI Nov 13 '21 at 18:55
I tried to minimze and explain as best as I can. Thank you for your comment – Tal Alter Nov 13 '21 at 19:17
I don't see `operator=` implemented in your code. – n. m. could be an AI Nov 13 '21 at 19:26
Also see update. – n. m. could be an AI Nov 13 '21 at 19:28
Do you mean to do something like Workout *w = &tmp[0] and then sort w? – Tal Alter Nov 13 '21 at 19:52
I mean `std::vector>`. – n. m. could be an AI Nov 13 '21 at 21:45
I tried to use smart pointers and I think I did it good altought I dont feel very comfortable with that object so maybe I did something worng. Can you please take a look and see if i did it correctly? Its still gives me the same error. Thank you so much I really appreciate it – Tal Alter Nov 14 '21 at 10:07
If you have a question about unique_ptr, please post a separate question, and include a [mcve] relevant to that question. Your question as it stands now is a mess and it isn't clear which code you are asking about. – n. m. could be an AI Nov 14 '21 at 10:38
Anyway, look at [this](https://godbolt.org/z/Yxo4sndd1), your errors with unique_ptr are because unique_ptr is not copyable, you need to pass it by reference or move it. – n. m. could be an AI Nov 14 '21 at 10:51

Sorting vector of objects c++ raise C2280 error

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