Source of function_object.cpp

Structures and functions

class DoubleClass

  1: //function_object.cpp
  2: //Illustrates a "function object", which is just an object of
  3: //a class that overloads the "function operator" operator().
  4: //In other words, it's a class object that behaves like a function.
  5: //The term "functor" is also used to mean "function object".

  7: #include <iostream>
  8: using namespace std;

 10: class DoubleClass
 11: {
 12: public:
 13:     int operator()(int i)
 14:     {
 15:         return 2*i;
 16:     }
 17: };

 19: int main()
 20: {
 21:     cout << "\nThis program illustrates a very simple function object, "
 22:             "or \"functor\". You need\nto study the source code to see "
 23:             "how the values shown below are produced.";
 24:     cout << "\nPress Enter to continue ... ";  cin.ignore(80, '\n');

 26:     DoubleClass f;

 28:     cout << endl;
 29:     cout << f(6)  << endl;
 30:     cout << f(-5) << endl;

 32:     //Actually the above syntax is shorthand for:
 33:     cout << f.operator()(6) << endl;
 34:     cout << f.operator()(-5) << endl;
 35:     cout << "\nPress Enter to continue ... ";  cin.ignore(80, '\n');
 36: }