CODEWITHSUNDEEP
c++sortingoperator-overloading
Hieu Doan
Hieu Doan

Reputation: 165

My overloading operator < don't apply to sort function in cpp

I want to overload operator < between 2 pair. It works when i compare using < but it doesn't work when i use sort function built_in cpp. #include using namespace std;

typedef pair<int,int> pii;

bool operator < (const pii &a,const pii &b){
    return a.second<b.second;
}

int main()
{
    pii a,b;
    a=make_pair(1,4);
    b=make_pair(2,3);
    if(a<b) cout<<"a<b\n";
    else cout<<"b<a\n";

    vector<pii> v;
    v.push_back(a);
    v.push_back(b);
    sort(v.begin(),v.end());

    for(auto x:v)
        cerr<<x.first<<" "<<x.second<<endl;

    return 0;
}

Output: 

b<a
1 4
2 3

I 'm confused why it doesn't print:

b<a
2 3
1 4

Upvotes: 3

Views: 92

Answers (1)

super
super

Reputation: 12928

std::pair already has a built in operator<. If you want to sort by a different criteria you can pass a comparison function.

std::sort(v.begin(),v.end(), [](auto& lhs, auto& rhs){ return lhs.second < rhs.second; });

Upvotes: 7

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