C/C++ “binary_function”: 不是 “std” 的成员-猿说编程

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一.binary_function简介

官方文章：https://en.cppreference.com/w/cpp/utility/functional/binary_function


 C++ Utilities library Function objects 
Defined in header <functional>
template<
    class Arg1,
    class Arg2,
    class Result
> struct binary_function;
(deprecated in C++11)
(removed in C++17)
binary_function is a base class for creating function objects with two arguments.

binary_function does not define operator(); it is expected that derived classes will define this. binary_function provides only three types - first_argument_type, second_argument_type and result_type - defined by the template parameters.

Some standard library function object adaptors, such as std::not2, require the function objects they adapt to have certain types defined; std::not2 requires the function object being adapted to have two types named first_argument_type and second_argument_type. Deriving function objects that take two arguments from binary_function is an easy way to make them compatible with those adaptors.

binary_function is deprecated in C++11 and removed in C++17.

binary_function is deprecated in C++11 and removed in C++17.（c++17已经移除了 binary_function）；