std::unary_function
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unary_function
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(until C++17*)(until C++17*)(until C++17*)(until C++17*)
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Defined in header
<functional>
template< typename ArgumentType, typename ResultType >
struct unary_function;
(deprecated in C++11) struct unary_function;
(removed in C++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 C++11.
[edit] Member types
Type
Definition
argument_type
ArgumentType
result_type
ResultType
[edit] 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())); // C++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
[edit] See also
(C++23)
(class template) [edit]
(deprecated in C++11)(removed in C++17)
(function template) [edit]
(deprecated in C++11)(removed in C++17)
(class template) [edit]
(deprecated in C++11)(removed in C++17)
(class template) [edit]