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unary_function<> Structure 

Illustrates how to use the unary_function<> structure in Visual C++.


template<class _A, class _R>
   struct unary_function
   {
      typedef _A Argument_Type;
      typedef _R Result_Type;
   };

NoteNote

The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.

unary_function is used as a base class to better define operator functions in the following format: Result_Type classname::operatorX(Argument_Type).

// unary_function.cpp
// compile with: /EHsc
//
// Structure used:
//       unary_function<int, float> - allows us
//       to write operator functions accepting an
//       integer and returning floats.
////////////////////////////////////////////

#include <functional>
#include <iostream>

using namespace std ;

/* derive class from unary_function in order to use it */

class unary_test : public unary_function<int,float>
{
public:
  float value;
  unary_test(){value=10.0;}
  unary_test(float x){value=x;}
  result_type operator*(argument_type x);
  result_type operator-(argument_type x);
};

/* You can now easily create operators that accept */
/* an int and return a float.                     */

unary_test::result_type unary_test::operator*(unary_test::argument_type x)
{
  float tmp = value * (float)x;
  cout << "Value after * is " << tmp << endl ;
  return value;
}

unary_test::result_type unary_test::operator-(unary_test::argument_type x)
{
  float tmp = value - (float)x;
  cout << "Value after minus is " << tmp << endl ;
  return tmp;
}

int main(void)
{
  unary_test item;
  unary_test item2(18.0);

  cout << "Begin" << endl ;
  cout.setf(ios::fixed) ;
  item = item * 2;
  item2 = item2 - 5;
}

Output

Begin
Value after * is 20.000000
Value after minus is 13.000000

Header: <functional>

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