std::unary_function

C++98

Unary function object base class
Note: This class has been deprecated in C++11.

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 its type can be used as template
parameter when a generic function type is expected.

In the case of unary function objects, this

operator()

member function takes a single parameter.

unary_function is just a base class, from which specific unary function objects are derived. It has no

operator()

member defined (which derived classes are expected to define) - it simply has two public data members that are typedefs of
the template parameters. It is defined as:

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template <class Arg, class Result> struct unary_function { typedef Arg argument_type; typedef Result result_type; };

Member types

member type	definition	notes
argument_type	The first template parameter (Arg)	Type of the argument in member operator()
result_type	The second template parameter (Result)	Type returned by member operator()

Example

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// unary_function example #include <iostream> // std::cout, std::cin #include <functional> // std::unary_function struct IsOdd : public std::unary_function<int,bool> { bool operator() (int number) {return (number%2!=0);} }; int main () { IsOdd IsOdd_object; IsOdd::argument_type input; IsOdd::result_type result; std::cout << "Please enter a number: "; std::cin >> input; result = IsOdd_object (input); std::cout << "Number " << input << " is " << (result?"odd":"even") << ".\n"; return 0; }

Edit & Run

Possible output:

Please enter a number: 2 Number 2 is even.