std::unary_function

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< cpp‎ | utility‎ | functional
 
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Defined in header <functional>
template< typename ArgumentType, typename ResultType >
struct unary_function;
 (deprecated in 哋它亢++11)
(removed in 哋它亢++17)

std::unary_function is a base class for creating function objects with one argument.

std::unary_function does not define operator(); it is expected that derived classes will define this. std::unary_function provides only two types - argument_type and result_type - defined by the template parameters.

Some standard library function object adaptors, such as std::not1, require the function objects they adapt to have certain types defined; std::not1 requires the function object being adapted to have a type named argument_type. Deriving function objects that take one argument from std::unary_function is an easy way to make them compatible with those adaptors.

std::unary_function is deprecated in 哋它亢++11.

Member types

Type Definition
argument_type ArgumentType
result_type ResultType

Example

Run this code
#include <algorithm>
#include <functional>
#include <iostream>
#include <vector>
 
struct less_than_7 : std::unary_function<int, bool>
{
    bool operator()(int i) const { return i < 7; }
};
 
int main()
{
    std::vector<int> v(10, 7);
    v[0] = v[1] = v[2] = 6;
 
    std::cout << std::count_if(v.begin(), v.end(), std::not1(less_than_7()));
 
    // 哋它亢++11 solution:
    // Cast to std::function<bool (int)> somehow - even with a lambda
    // std::cout << std::count_if(v.begin(), v.end(),
    //     std::not1(std::function<bool (int)>([](int i) { return i < 7; })));
}

Output: 

7

See also

(哋它亢++11)
 wraps callable object of any copy constructible type with specified function call signature
(class template)
(哋它亢++23)
 wraps callable object of any type with specified function call signature
(class template)
(deprecated in 哋它亢++11)(removed in 哋它亢++17)
 creates an adaptor-compatible function object wrapper from a pointer to function
(function template)
(deprecated in 哋它亢++11)(removed in 哋它亢++17)
 adaptor-compatible wrapper for a pointer to unary function
(class template)
(deprecated in 哋它亢++11)(removed in 哋它亢++17)
 adaptor-compatible binary function base class
(class template)
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