Using a function object for operation counting, second version : Functor « Development

Using a function object for operation counting, second version : Functor « Development « C++ Tutorial

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C++ Tutorial » Development » Functor

5.15.4.Using a function object for operation counting, second version

//Revised from

//STL Tutorial and Reference Guide C++ Programming with the Standard Template L

ibrary, 2nd Edition

//by David R. Musser (Author), Atul Saini (Author)

//# Publisher: Addison-Wesley Pub (Sd) (March 1996)

//# Language: English

//# ISBN-10: 0201633981

//# ISBN-13: 978-0201633986



#include <iostream>

#include <iomanip>

#include <cassert>

#include <vector>

#include <algorithm>

#include <functional>

using namespace std;

template <typename T>

class less_with_count : public binary_function<T, T, bool> {

public:

  less_with_count() : counter(0), progenitor(0) { }

  // Copy constructor:

  less_with_count(less_with_count<T>& x) : counter(0), 

      progenitor(x.progenitor ? x.progenitor : &x) { }

  bool operator()(const T& x, const T& y) {

    ++counter;

    return x < y;

  }

  long report() const { return counter; }

  ~less_with_count() {  // Destructor

    if (progenitor) {

      progenitor->counter += counter; 

    }

  }

private:

  long counter;

  less_with_count<T>* progenitor;

};

int main()

{

  cout << "Using a function object for operation counting, "

       << "second version." << endl;

  const long N1 = 1000, N2 = 128000;

  for (long N = N1; N <= N2; N *= 2) { 

    vector<int> vector1;

    for (int k = 0; k < N; ++k) 

      vector1.push_back(k);

    random_shuffle(vector1.begin(), vector1.end());

    less_with_count<int> comp_counter;

    sort(vector1.begin(), vector1.end(), comp_counter);

    cout << "Problem size " << setw(9) << N 

         << ",  comparisons performed: " 

         << setw(9) << comp_counter.report() << endl;

  }

  return 0;

}

Using a function object for operation counting, second version.
Problem size      1000,  comparisons performed:     11846
Problem size      2000,  comparisons performed:     26397
Problem size      4000,  comparisons performed:     56776
Problem size      8000,  comparisons performed:    125715
Problem size     16000,  comparisons performed:    271505
Problem size     32000,  comparisons performed:    596740
Problem size     64000,  comparisons performed:   1235889
Problem size    128000,  comparisons performed:   2727581

5.15.Functor
	5.15.1.	Functor
	5.15.2.	Functor compose 2
	5.15.3.	Functor compose 3
	5.15.4.	Using a function object for operation counting, second version
	5.15.5.	Using a function object for operation counting, first version
	5.15.6.	Demonstrating function pointer passing

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