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

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//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