STL Sample for the unary_functi

• The Standard C++ Library included with: - Microsoft Visual C++, 32-bit Edition, version 4.2

SUMMARY

The sample code below illustrates how to use the unary_function STL structure in Visual C++.

MORE INFORMATION

Required Header

   < functional >

Prototype

   template<class _A, class _R>
   struct unary_function
   {
     typedef _A argument_type;
     typedef _R result_type;
   };

Description

unary_function is used as a base class to allow us to better define operator functions in the following format:

   result_type classname::operatorX(argument_type)

Sample Code

////////////////////////////////////////////
//
// Compile options needed: none
//
// Structure used:
//       unary_function<int, float> - allows us
//       to write operator functions accepting an
//       integer and returning floats.
//
// Written by Mark Hagen
// of Microsoft Product Support Services,
// Copyright (c) 1996 Microsoft Corporation.
// All rights reserved.
////////////////////////////////////////////

#include <functional>
#include <iostream>

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

  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.                     */

  value*=x;
  cout << "New value after * is " << value << endl ;
  return value;

unary_test::result_type unary_test::operator-(unary_test::argument_type x) {

  value-+(float)x;
  cout << "New value after minus is " << value << endl ;

  return value;

void main(void)

  unary_test item;
  unary_test item2(18.0);

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

Program Output is:

Begin New value after * is 20.000000 New value after minus is 18.000000

REFERENCES

Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference.