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 <iostream>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <cmath>
#include <cstddef>
#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.));
// an equivalent lambda is: [pi](double a){ return a*pi / 180.; });

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