std::bind1st,std::bind2nd(3)

NAME
std::bind1st,std::bind2nd - std::bind1st,std::bind2nd

Synopsis
   Defined in header <functional>
   template< class F, class T > (1) (deprecated in C++11)
   std::binder1st<F> bind1st( const F& f, const T& x ); (removed in C++17)
   template< class F, class T > (2) (deprecated in C++11)
   std::binder2nd<F> bind2nd( const F& f, const T& x ); (removed in C++17)
   Binds a given argument x to a first or second parameter of the given binary function
   object f. That is, stores x within the resulting wrapper, which, if called, passes x
   as the first or the second parameter of f.
   1) Binds the first argument of f to x. Effectively calls std::binder1st<F>(f,
   typename F::first_argument_type(x)).
   2) Binds the second argument of f to x. Effectively calls std::binder2nd<F>(f,
   typename F::second_argument_type(x)).

Parameters
   f - pointer to a function to bind an argument to
   x - argument to bind to f

Return value
   A function object wrapping f and x.

Exceptions
   May throw implementation-defined exceptions.

Example
// Run this code
 #include <algorithm>
 #include <cmath>
 #include <cstddef>
 #include <functional>
 #include <iomanip>
 #include <iostream>
 #include <vector>
 int main()
 {
     std::vector<double> a = {0, 30, 45, 60, 90, 180};
     std::vector<double> r(a.size());
     const double pi = std::acos(-1); // since C++20 use std::numbers::pi
     std::transform(a.begin(), a.end(), r.begin(),
         std::bind1st(std::multiplies<double>(), pi / 180.0));
 // an equivalent lambda is: [pi](double a) { return a * pi / 180.0; });
     for (std::size_t n = 0; n < a.size(); ++n)
         std::cout << std::setw(3) << a[n] << "° = " << std::fixed << r[n]
                   << " rad\n" << std::defaultfloat;
 }

Output:
   0° = 0.000000 rad
  30° = 0.523599 rad
  45° = 0.785398 rad
  60° = 1.047198 rad
  90° = 1.570796 rad
 180° = 3.141593 rad

See also
   binder1st function object holding a binary function and one
   binder2nd of its arguments
   (deprecated in C++11)(removed in (class template)
   C++17)
   bind_front bind a variable number of arguments, in order, to a
   bind_back function object
   (C++20) (function template)
   (C++23)