Microsoft KB Archive/158232

= STL Sample for the unary_functi =

Article ID: 158232

Article Last Modified on 11/18/2003

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APPLIES TO


 * Microsoft Visual C++ 4.2 Enterprise Edition
 * Microsoft Visual C++ 4.2 Professional Edition
 * The Standard C++ Library

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This article was previously published under Q158232



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



Prototype
template 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 - 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. ////////////////////////////////////////////

using namespace std;
 * 1) include
 * 2) include

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

class unary_test : public unary_function { 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

