unary_function Program in C++

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This C++ program illustrates unary function object base. The DivisibleByFour inherits from the unary_function object base defined in functional library and is passed as a predicate to the for_each algorithm. The elements of vector which are divisible by four are printed.

Here is the source code of the C++ program illustrates unary function object base. The C++ program is successfully compiled and run on a Linux system. The program output is also shown below.

  1. /*
  2.  * C++ Program to illustrate unary function objects bases 
  3.  */
  4. #include <iostream>
  5. #include <functional>
  6. #include <vector>
  7. #include <algorithm>
  8.  
  9. struct DivisibleByFour : public std::unary_function<int, bool> {
  10.     bool operator() (int value)
  11.     {
  12.         if ((value % 4) == 0)
  13.         {
  14.             std::cout << value << " ";
  15.             return true;
  16.         }
  17.         else
  18.             return false;
  19.     }
  20. };
  21.  
  22. int main()
  23. {
  24.     DivisibleByFour d;
  25.     std::vector <int> v(20);
  26.  
  27.     for (int i = 0; i < 20; i++)
  28.         v[i] = i + 1;
  29.     std::cout << "Range 1 : 20 " << std::endl;
  30.     std::cout << "Elements divisible by 4 : ";
  31.     std::for_each(v.begin(), v.end(), d);
  32.     std::cout << std::endl;
  33. }

$ a.out
Range 1 : 20 
Elements divisible by 4 : 4 8 12 16 20

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