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Showing content from https://cplusplus.com/reference/functional/binary_negate/ below:

class template

std::binary_negate

template <class Predicate> class binary_negate;

Negate binary function object class

Binary function object class whose call returns the opposite of another binary function, passed to its constructor.

Object of type binary_negate are generally constructed using function not2.

The class is defined with the same behavior as:

template <class Predicate> class binary_negate
  : public binary_function <typename Predicate::first_argument_type,
                            typename Predicate::second_argument_type, bool>
{
protected:
  Predicate fn_;
public:
  explicit binary_negate ( const Predicate& pred ) : fn_ (pred) {}
  bool operator() (const typename Predicate::first_argument_type& x,
                   const typename Predicate::second_argument_type& y) const
  { return !fn_(x,y); }
};

template <class Predicate> class binary_negate
{
protected:
  Predicate fn_;
public:
  explicit binary_negate (const Predicate& pred) : fn_ (pred) {}
  bool operator() (const typename Predicate::argument_type& x) const {return !fn_(x,y);}
  typedef typename Predicate::first_argument_type  first_argument_type;
  typedef typename Predicate::second_argument_type second_argument_type;
  typedef bool result_type;
};

Template parameters

Predicate: A binary function object class, with members first_argument_type and second_argument_type defined.

Member types member type definition notes first_argument_type T Type of the first argument in member operator() second_argument_type T Type of the second argument in member operator() result_type T Type returned by member operator()
Member functions

constructor: Constructs an object whose functional call returns the opposite as the object passed as its argument.
operator(): Member function returning the opposite of the function object with which the object was constructed.

Example

// binary_negate example
#include <iostream>     // std::cout
#include <functional>   // std::binary_negate, std::equal_to
#include <algorithm>    // std::mismatch
#include <utility>      // std::pair

int main () {
  std::equal_to<int> equality;
  std::binary_negate < std::equal_to<int> > nonequality (equality);
  int foo[] = {10,20,30,40,50};
  int bar[] = {0,15,30,45,60};
  std::pair<int*,int*> firstmatch,firstmismatch;
  firstmismatch = std::mismatch (foo,foo+5,bar,equality);
  firstmatch = std::mismatch (foo,foo+5,bar,nonequality);
  std::cout << "First mismatch in bar is " << *firstmismatch.second << "\n";
  std::cout << "First match in bar is " << *firstmatch.second << "\n";
  return 0;
}

Output:

First mismatch in bar is 0
First match in bar is 30