CODEWITHSUNDEEP
c++hashmap
user1781302
user1781302

Reputation: 11

C++: Counting number of equality comparison in hash map

I have an unordered map with user-defined hash and equality functions.

I would like to count the number of times equality comparison function is called after adding all the elements to the map. Is there an easy way to do this?

Upvotes: 1

Views: 126

Answers (1)

BigBoss
BigBoss

Reputation: 6914

In your custom equality function count them:

struct equality_comparer : std::binary_function<MyType, MyType, bool> {
    static int counter_;

    bool operator()( MyType const& lhs, MyType const& rhs ) {
        ++counter_;
        return lhs == rhs;
    }
};
int equality_comparer::counter_ = 0;

And then after insertion to the map complete: equality_comparer::counter_ = 0.

As mentioned by @PiotrNycz you can use this:

struct equality_comparer : std::binary_function<MyType, MyType, bool> {
    mutable int counter_;
  //^^^^^^^
    equality_comparer() : counter_(0) {}
    bool operator()( MyType const& lhs, MyType const& rhs ) {
        ++counter_;
        return lhs == rhs;
    }
    void reset_counter() {counter_ = 0;}
};

Then you can have myMap.key_eq().reset_counter() instead of equality_comparer::counter_ = 0 in previous code and myMap.key_eq().counter_ to access counter value.

Upvotes: 2

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