std::bind1st, std::bind2nd

 

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unary_function (until C++17) binary_function (until C++17) ptr_fun (until C++17) pointer_to_unary_function (until C++17) pointer_to_binary_function (until C++17) mem_fun (until C++17) mem_fun_tmem_fun1_tconst_mem_fun_tconst_mem_fun1_t (until C++17)(until C++17)(until C++17)(until C++17) not1 (until C++20) not2 (until C++20)	binder1stbinder2nd (until C++17)(until C++17) bind1stbind2nd (until C++17)(until C++17) mem_fun_ref (until C++17) mem_fun_ref_tmem_fun1_ref_tconst_mem_fun_ref_tconst_mem_fun1_ref_t (until C++17)(until C++17)(until C++17)(until C++17) unary_negate (until C++20) binary_negate (until C++20)

 

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

(none)

Example

Run this code

#include <iostream>
#include <algorithm>
#include <functional>
#include <cmath>
#include <vector>
 
int main()
{
    std::vector<double> a= {0, 30, 45, 60, 90, 180};
    std::vector<double> r(a.size());
    double pi = std::acos(-1);
 
    std::transform(a.begin(), a.end(), r.begin(),
        std::bind1st(std::multiplies<double>(), pi / 180.));
// equivalent lambda: [pi](double a){ return a*pi/180.; });
 
    for(size_t n = 0; n < a.size(); ++n)
        std::cout << a[n] << " deg = " << r[n] << " rad\n";
}

Output:

0 deg = 0 rad
30 deg = 0.523599 rad
45 deg = 0.785398 rad
60 deg = 1.0472 rad
90 deg = 1.5708 rad
180 deg = 3.14159 rad

See also

binder1stbinder2nd (deprecated in C++11)(removed in C++17)

function object holding a binary function and one of its arguments (class template)