std::binary_function(3)

NAME
std::binary_function - std::binary_function

Synopsis
   Defined in header <functional>
   template<
       class Arg1, (deprecated in C++11)
       class Arg2, (removed in C++17)
       class Result
   > struct binary_function;
   std::binary_function is a base class for creating function objects with two
   arguments.
   std::binary_function does not define operator(); it is expected that derived classes
   will define this. std::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
   std::binary_function is an easy way to make them compatible with those adaptors.
   std::binary_function is deprecated in C++11 and removed in C++17.

Member types
   Type Definition
   first_argument_type Arg1
   second_argument_type Arg2
   result_type Result

Example
// Run this code
 #include <algorithm>
 #include <functional>
 #include <iostream>
 #include <vector>
 struct same : std::binary_function<int, int, bool>
 {
     bool operator()(int a, int b) const { return a == b; }
 };
 int main()
 {
     std::vector<char> v1{'A', 'B', 'C', 'D', 'E'};
     std::vector<char> v2{'E', 'D', 'C', 'B', 'A'};
     std::vector<bool> v3(v1.size());
     std::transform(v1.begin(), v1.end(), v2.begin(), v3.begin(), std::not2(same()));
     std::cout << std::boolalpha;
     for (std::size_t i = 0; i < v1.size(); ++i)
         std::cout << v1[i] << " != " << v2[i] << " : " << v3[i] << '\n';
 }

Output:
 A != E : true
 B != D : true
 C != C : false
 D != B : true
 E != A : true

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