std:: bind1st, std:: bind2nd

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bind1st bind2nd
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Defined in header <functional>
template < class F, class T >
std:: binder1st < F > bind1st ( const F & f, const T & x ) ;
(1) (deprecated in C++11)
(removed in C++17)
template < class F, class T >
std:: binder2nd < F > bind2nd ( const F & f, const T & x ) ;
(2) (deprecated in C++11)
(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

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