STL Sample for the unary_functi

ID: Q158232

The information in this article applies to:

Microsoft Visual C++, 32-bit Editions, version 4.2
The Standard C++ Library

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>

/* 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 : kbcode STLIss
Version : winnt:4.2
Platform : winnt
Issue type : kbhowto