Q158232: STL Sample for the unary_functi

Article: Q158232
Product(s): Microsoft C Compiler
Version(s): winnt:4.2
Operating System(s): 
Keyword(s): _IK
Last Modified: 06-MAY-2001

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The information in this article applies to:

- Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
- Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
- The Standard C++ Library 
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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;
     };

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

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>
  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)
  {
    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.

Additional query words: STL Sample unary_function

======================================================================
Keywords          : _IK 
Technology        : kbVCsearch kbAudDeveloper kbVC420 kbVC32bitSearch kbVCLibrary
Version           : winnt:4.2
Issue type        : kbhowto

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