CODEWITHSUNDEEP
c++
Dalton
Dalton

Reputation: 181

sorting a vector on its element's feature

First, I would like to thank people for having helped me so far. You are great!!!!! (if only you knew it)

typedef template<class T>struct 
{
   T homepet_;
   T wildpet_;
}Animal;

std::vector<Animal> va;
std::sort(va.begin(),va.end(),Pred<std::string>(sort_based_on_bool_and_arg));

I would like Pred(sort_based_on_bool_and_arg) used to sort vector based on
1. if user inputs true it is ascending or descending otherwise
2. if user inputs choose homepet_ as argument then it sorts for homepet_ or it will sort wildpet_

Upvotes: 1

Views: 148

Answers (2)

Tony The Lion
Tony The Lion

Reputation: 63250

I believe you need something along these lines: 

struct functor
{
    inline bool operator()(const Animal& a, const Animal& b) const
    {
        return (does a come before b);
    }
};

typedef std::vector<Animal> va;
va list;
std::sort(list.begin(), list.end(), functor()); //call operator() on functor

Upvotes: 2

Jan Hudec
Jan Hudec

Reputation: 76316

I don't know what Pred is supposed to be, but I do know it shouldn't be there.

sort takes a binary predicate on 2 (references to) members of the vector implementing strict weak ordering. A binary predicate can be either a function or an object with operator(). If you can compare two Animal objects, just create a function:

bool animal_less_than(const Animal &l, const Animal &r) { ... }

and call sort like:

std::sort(list.begin(), list.end(), &animal_less_than);

If you need some extra parameter, you'll need:

struct animal_less_than {
    type_of_extra_data extra_data;
    animal_less_than(type_of_extra_data extra_data) : extra_data(extra_data) {}
    bool operator()(const Animal &l, const Animal &r) { ... }
};

and call sort like:

std::sort(list.begin(), list.end(), animal_less_than(extra_data));

On a side note, the syntax declaring Animal is wrong. It should be:

template <typename T>
struct Animal {
    T homepet_;
    T wildpet_;
};

and for the matter, it should probably be a class rather than struct and should be encapsulated.

Upvotes: 1

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