std::binder1st, std::binder2nd

 

C++

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Concepts library (C++20)

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Utilities library

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Numerics library

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Atomic operations library (C++11)

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Technical Specifications

 

Utilities library

Type support (basic types, RTTI, type traits)
Dynamic memory management
Error handling
Program utilities
Variadic functions
Library feature-test macros
Date and time
Function objects
initializer_list (C++11)
bitset
hash (C++11)
integer_sequence (C++14)
Relational operators (deprecated in C++20)
rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
Comparisons (C++20)
strong_order weak_order partial_order strong_equal weak_equal	strong_ordering weak_ordering partial_ordering strong_equality weak_equality	is_eqis_neqis_ltis_lteqis_gtis_gteq
common_comparison_category
Common vocabulary types
pair tuple (C++11) apply (C++17) make_from_tuple (C++17)	optional (C++17) any (C++17) variant (C++17)
Swap, forward and move
swap
exchange (C++14)
forward (C++11)
move (C++11)
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chars_format (C++17)
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declval (C++11)
as_const (C++17)
launder (C++17)

 

Function objects

Function wrappers function (C++11) mem_fn (C++11) bad_function_call (C++11)	Partial function application bind_front (C++20) bind (C++11) is_bind_expression (C++11) is_placeholder (C++11) _1, _2, _3, ... (C++11)
Function invocation invoke (C++17) 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 logical_and logical_or logical_not	equal_to not_equal_to greater less greater_equal less_equal bit_and bit_or bit_xor bit_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)
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)

 

template< class Fn > class binder1st : public std::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,               const typename Fn::first_argument_type& value);     typename Fn::result_type         operator()(const typename 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 : public 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,               const typename Fn::second_argument_type& value);     typename Fn::result_type         operator()(const typename 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 though operator(), the stored value is passed as one of the arguments, the other argument is passed as an argument of operator(). The resulting function object is an unary function.

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

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

Example

Run this code

#include <iostream>
#include <functional>
#include <cmath>
#include <vector>
const double pi = std::acos(-1);
int main()
{
    // deprecated in C++11, removed in C++17
    std::binder1st<std::multiplies<double>> f1 = std::bind1st(
                                                   std::multiplies<double>(), pi / 180.);
 
    // C++11 replacement
    auto f2 = [](double a){ return a*pi/180.; };
 
    for(double n : {0, 30, 45, 60, 90, 180})
        std::cout << n << " deg = " << f1(n) << " rad (using binder) "
                                    << f2(n) << " rad (using lambda)\n";
}

Output:

0 deg = 0 rad (using binder) 0 rad (using lambda)
30 deg = 0.523599 rad (using binder) 0.523599 rad (using lambda)
45 deg = 0.785398 rad (using binder) 0.785398 rad (using lambda)
60 deg = 1.0472 rad (using binder) 1.0472 rad (using lambda)
90 deg = 1.5708 rad (using binder) 1.5708 rad (using lambda)
180 deg = 3.14159 rad (using binder) 3.14159 rad (using lambda)

See also

bind1stbind2nd (deprecated in C++11)(removed in C++17)

binds one argument to a binary function (function template)