CODEWITHSUNDEEP
c++listsetoverloading
Ediolot
Ediolot

Reputation: 521

set (c++) and operator < overload

I have some classes, one for example is something like:

class foo {

    private:
        int number;
        ...

    public:

        foo(int set_number):number(set_number) {}
        ...

        bool operator<(const foo &myfoo) const
        { 
            return (number < myfoo.number ? 1 : 0); 
        }
        /* operator < */

        bool operator==(const foo &myfoo) const
        { 
             return (number == myfoo.number ? 1 : 0); 
        }
        /* operator == */

        ...
};

And I was using something similar to this class with set:

class hello {
    private:
        set<foo*> list;
        set<int>  int_list;
        ...
    public:
        ...
        fillList(void)
        {
           for(int i=0; i<10; i++)
           {
              list.insert(new foo(i));
              int_list.insert(i);
           }
        }
        ...
};

Ok, so when I print the result I get:

int_list: 0, 1, 2, 3, 4, ... 
list: 0, 6, 4, 5, ... (Using a method to print the attribute "number" from the object foo).

Obviusly the second is not ok. I guess it has to do with the fact that set is made of pointers, not of objects.

Now, should I use my set just like set< foo > ? Or is there a solution for this using pointers ?. Maybe I can overload the operators using something like:

bool operator<(const *foo myvar, const *foo myvar2);

I was using this "set< foo* >". Because I was taught to use this way in vector< type > objects.

What's the best option ?

Upvotes: 0

Views: 75

Answers (1)

lilezek
lilezek

Reputation: 7344

If you want a custom sorting in set, you can't override < operator because:

set<foo*>

Its a set of pointers. Use instead:

set<foo*, compare>

And:

struct compare {
    bool operator() (const foo * lhs, const foo * rhs) const{
        return lhs->operator<(*rhs);
    }
};

Reason

Your set is sorting pointers. If you add compare to set<foo*, compare>, you force to use the < operator of the pointed class.

Alternative not using pointers

Just use set<foo> and remove new from list.insert(new foo(i));.

Upvotes: 1

Related Questions