CODEWITHSUNDEEP
c++comparator
Mateus de Oliveira
Mateus de Oliveira

Reputation: 111

Passing Parameters to Comparators

I would like to pass a map "m" as a parameter for a comparator to be used with the sort function. 

bool comparator(const myType A, const myType B, map<Mytype,int> m){
      return m.find(A) < m.find(B); 
}

Note that the comparator changes depending on m. Now, how could I use such comparator with the sort function? When I try the code below the compiler complains about the number of arguments in the comparator function.

void SortingVector(vector<myType> V, map<myType,int> m){
     sort(V.begin(),V.end(),comparator); 
}

So what is the easiest way, using STD machinery to define such a parameterized comparator?

Upvotes: 1

Views: 500

Answers (1)

Jodocus
Jodocus

Reputation: 7591

Use a lambda closure:

void SortingVector(vector<myType>& V, const map<myType,int>& m){
    sort(V.begin(),V.end(), [&m](const myType& A, const myType& B) {
      return m.find(A) < m.find(B); 
    }); 
}

As a side note: I added various references, for both effectiveness and correctness, as your sort function otherwise would just sort a copied vector and throws it away after it ran out of scope.

Upvotes: 3

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