Illustrates how to use the unary_function<> structure in Visual C++.
template<class _A, class _R>
struct unary_function
{
typedef _A argument_type;
typedef _R result_type;
};
Remarks
备注
The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.
unary_function is used as a base class to better define operator functions in the following format: Result_Type classname::operatorX(Argument_Type).
Example
// unary_function.cpp
// compile with: /EHsc
//
// Structure used:
// unary_function<int, float> - allows us
// to write operator functions accepting an
// integer and returning floats.
////////////////////////////////////////////
#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)
{
float tmp = value * (float)x;
cout << "Value after * is " << tmp << endl ;
return value;
}
unary_test::result_type unary_test::operator-(unary_test::argument_type x)
{
float tmp = value - (float)x;
cout << "Value after minus is " << tmp << endl ;
return tmp;
}
int main(void)
{
unary_test item;
unary_test item2(18.0);
cout << "Begin" << endl ;
cout.setf(ios::fixed) ;
item = item * 2;
item2 = item2 - 5;
}
Begin Value after * is 20.000000 Value after minus is 13.000000
Requirements
Header: <functional>