class template
std::unary_function
<functional>
template <class Arg, class Result> struct unary_function;
Unary function object base class
This is a base class for standard
unary function objects.
Generically,
function objects are instances of a class with member function
operator() defined. This member function allows the object to be used with the same syntax as a regular function call, and therefore it can be used in templates instead of a pointer to a function.
In the case of
unary function objects, this
operator() member function takes one single parameter.
unary_function is just a base class, from which specific unary function objects are derived. It has no
operator() member defined (derived classes are expected to define this) - it simply has two public data members that are
typedefs of the template parameters. It is defined as:
1 2 3 4 5
|
template <class Arg, class Result>
struct unary_function {
typedef Arg argument_type;
typedef Result result_type;
};
|
Members
- argument_type
- Alias of the first template parameter, which is the type for the argument in member operator().
- result_type
- Alias of the second template parameter, which is the return type in member operator().
Example
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
|
// unary_function example
#include <iostream>
#include <functional>
using namespace std;
struct IsOdd : public unary_function<int,bool> {
bool operator() (int number) {return (number%2==1);}
};
int main () {
IsOdd IsOdd_object;
IsOdd::argument_type input;
IsOdd::result_type result;
cout << "Please enter a number: ";
cin >> input;
result = IsOdd_object (input);
cout << "Number " << input << " is " << (result?"odd":"even") << ".\n";
return 0;
}
|
Possible output:
Please enter a number: 2
Number 2 is even.
|
See also
- binary_function
- Binary function object base class (class template)