std::bind1st, std::bind2nd

Header: <functional>

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.

# Declarations

template< class F, class T >
std::binder1st<F> bind1st( const F& f, const T& x );

(deprecated in C++11) (removed in C++17)

template< class F, class T >
std::binder2nd<F> bind2nd( const F& f, const T& x );

(deprecated in C++11) (removed in C++17)

# Parameters

# Return value

A function object wrapping f and x.

# Example

#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;
}

# See also