The sample code below illustrates how to use the unary_function
STL structure in Visual C++.
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Required Header
<functional>
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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.
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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)
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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
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Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library
Reference.
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This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.
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