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

class template

std::pointer_to_binary_function

template <class Arg1, class Arg2, class Result> class pointer_to_binary_function;

Generate binary function object class from pointer

Generates a binary function object class from a pointer to a function that takes two arguments (of type

Arg1

and

Arg2

) and returns a value (of type

Result

pointer_to_binary_function is generally used as a type. The function ptr_fun (also defined in header <functional>) can be used to directly construct an object of this type.

This class is derived from binary_function and is typically defined as:

template <class Arg1, class Arg2, class Result>
  class pointer_to_binary_function : public binary_function <Arg1,Arg2,Result>
{
protected:
  Result(*pfunc)(Arg1,Arg2);
public:
  explicit pointer_to_binary_function ( Result (*f)(Arg1,Arg2) ) : pfunc (f) {}
  Result operator() (Arg1 x, Arg2 y) const
    { return pfunc(x,y); }
};

Members

constructor: Constructs a binary function object class from pointer to a function that takes two arguments of types Arg1 and Arg2, and returns a value of type Result.
operator(): Member function taking two parameters, passing them to the function pointed by the pointer used at construction, and forwarding the return value obtained as its own return value.

Example

// pointer_to_binary_function example
#include <iostream>
#include <functional>
#include <algorithm>
#include <cmath>
using namespace std;

int main () {
  pointer_to_binary_function <double,double,double> PowObject (pow);
  double numbers[] = {1.0, 2.0, 3.0, 4.0, 5.0};
  double squares[5];
  transform (numbers, numbers+5, squares, bind2nd(PowObject,2) );
  for (int i=0; i<5; i++)
    cout << squares[i] << " ";
  cout << endl;
  return 0;
}

Possible output: