std::binder1st,std::binder2nd

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Standard library
Standard library headers
Named requirements
Feature test macros(C++20)
Language support library
Concepts library(C++20)
Diagnostics library
Memory management library
Metaprogramming library(C++11)
General utilities library
Containers library
Iterators library
Ranges library(C++20)
Algorithms library
Strings library
Text processing library
Numerics library
Date and time library
Input/output library
Filesystem library(C++17)
Concurrency support library(C++11)
Execution control library(C++26)
Technical specifications
Symbols index
External libraries

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Utilities library

Language support

Type support (basic types, RTTI)

Library feature-test macros(C++20)

Program utilities

Variadic functions

initializer_list

(C++11)

is_constant_evaluated

(C++20)

is_within_lifetime

(C++26)

source_location

(C++20)

Coroutine support(C++20)

Contract support(C++26)

Three-way comparison

three_way_comparablethree_way_comparable_with

(C++20)(C++20)

strong_ordering

(C++20)

weak_ordering

(C++20)

partial_ordering

(C++20)

common_comparison_category

(C++20)

compare_three_way_result

(C++20)

(C++20)

(C++20)

(C++20)

(C++20)

compare_strong_order_fallback

(C++20)

compare_weak_order_fallback

(C++20)

compare_partial_order_fallback

(C++20)

is_eqis_ltis_lteq

(C++20)(C++20)(C++20)

is_neqis_gtis_gteq

(C++20)(C++20)(C++20)

General utilities

Function objects
Bit manipulation(C++20)
C-style bit manipulation(C++26)
bitset
hash (C++11)

Relational operators(deprecated in C++20)

rel_ops::operator!=rel_ops::operator>

rel_ops::operator<=rel_ops::operator>=

Integer comparison functions

cmp_equalcmp_lesscmp_less_than

(C++20)(C++20)(C++20)

cmp_not_equalcmp_greatercmp_greater_than

(C++20)(C++20)(C++20)

in_range

(C++20)

Swap andtype operations

swap
ranges::swap (C++20)
exchange (C++14)
declval (C++11)
to_underlying (C++23)

forward (C++11)
forward_like (C++23)
move (C++11)
move_if_noexcept (C++11)
as_const (C++17)

Common vocabulary types

pair
tuple (C++11)
optional (C++17)
any (C++17)
variant (C++17)

tuple_size (C++11)
tuple_element (C++11)
apply (C++17)
make_from_tuple (C++17)
expected (C++23)

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Function objects

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)

Function invocation
invokeinvoke_r (C++17)(C++23)
Identity function object
identity (C++20)

Reference wrappers
reference_wrapper (C++11)
refcref (C++11)(C++11)
unwrap_referenceunwrap_ref_decay (C++20)(C++20)

Operator wrappers

plus
minus
negate
multiplies
divides
modulus
bit_and
bit_or
bit_not (C++14)
bit_xor

equal_to
not_equal_to
greater
less
greater_equal
less_equal
logical_and
logical_or
logical_not

Transparent operator wrappers

plus<> (C++14)
minus<> (C++14)
negate<> (C++14)
multiplies<> (C++14)
divides<> (C++14)
modulus<> (C++14)
bit_and<> (C++14)
bit_or<> (C++14)
bit_not<> (C++14)
bit_xor<> (C++14)

equal_to<> (C++14)
not_equal_to<> (C++14)
greater<> (C++14)
less<> (C++14)
greater_equal<> (C++14)
less_equal<> (C++14)
logical_and<> (C++14)
logical_or<> (C++14)
logical_not<> (C++14)

Negators
not_fn (C++17)
Searchers
default_searcher (C++17)
boyer_moore_searcher (C++17)
boyer_moore_horspool_searcher (C++17)

Constrained comparators
ranges::equal_to (C++20)
ranges::not_equal_to (C++20)
ranges::greater (C++20)
ranges::less (C++20)
ranges::greater_equal (C++20)
ranges::less_equal (C++20)
compare_three_way (C++20)

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*)

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Defined in header`<functional>`
template<class Fn> class binder1st :publicstd::unary_function<typename Fn::second_argument_type, typename Fn::result_type>{ protected: Fn op; typename Fn::first_argument_type value; public: binder1st(const Fn& fn, consttypename Fn::first_argument_type& value); typename Fn::result_type operator()(consttypename Fn::second_argument_type& x)const; typename Fn::result_type operator()(typename Fn::second_argument_type& x)const; };	(1)	(deprecated in C++11) (removed in C++17)
template<class Fn> class binder2nd :publicstd::unary_function<typename Fn::first_argument_type, typename Fn::result_type>{ protected: Fn op; typename Fn::second_argument_type value; public: binder2nd(const Fn& fn, consttypename Fn::second_argument_type& value); typename Fn::result_type operator()(consttypename Fn::first_argument_type& x)const; typename Fn::result_type operator()(typename Fn::first_argument_type& x)const; };	(2)	(deprecated in C++11) (removed in C++17)

A function object that binds an argument to a binary function.

The value of the parameter is passed to the object at the construction time and stored within the object. Whenever the function object is invoked thoughoperator(), the stored value is passed as one of the arguments, the other argument is passed as an argument ofoperator(). The resulting function object is a unary function.

1) Binds the first parameter to the valuevalue given at the construction of the object.

2) Binds the second parameter to the valuevalue given at the construction of the object.

[edit]Example

Run this code

#include <cmath>#include <functional>#include <iostream>#include <vector> constdouble pi=std::acos(-1);// use std::numbers::pi in C++20 int main(){// deprecated in C++11, removed in C++17auto f1=std::bind1st(std::multiplies<double>(), pi/180.0); // C++11 replacementauto f2=[](double a){return a* pi/180.0;}; for(double n:{0,30,45,60,90,180})std::cout<< n<<"°\t"<<std::fixed<<"= "<< f1(n)<<" rad (using binder)\t= "<< f2(n)<<" rad (using lambda)\n"<<std::defaultfloat;}

Output:

0°= 0.000000 rad (using binder)= 0.000000 rad (using lambda)30°= 0.523599 rad (using binder)= 0.523599 rad (using lambda)45°= 0.785398 rad (using binder)= 0.785398 rad (using lambda)60°= 1.047198 rad (using binder)= 1.047198 rad (using lambda)90°= 1.570796 rad (using binder)= 1.570796 rad (using lambda)180°= 3.141593 rad (using binder)= 3.141593 rad (using lambda)