std::bind1st, std::bind2nd

 

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Function wrappers function (C++11) move_only_function (C++23) copyable_function (C++26) function_ref (C++26) mem_fn (C++11) bad_function_call (C++11)	Partial function application bind_frontbind_back (C++20)(C++23) bind (C++11) is_bind_expression (C++11) is_placeholder (C++11) _1, _2, _3, ... (C++11)
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Old binders and adaptors
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

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());constdouble 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

binder1stbinder2nd (deprecated in C++11)(removed in C++17)	function object holding a binary function and one of its arguments (class template)
bind_frontbind_back (C++20)(C++23)	bind a variable number of arguments, in order, to a function object (function template)