std::binder1st, std::binder2nd

 

C++

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Feature test macros (C++20)

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Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

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Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

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Filesystem library (C++17)

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Technical specifications

Symbols index

External libraries

 

Utilities library

Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Dynamic memory management Program utilities Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) launder (C++17) initializer_list (C++11) source_location (C++20) Three-way comparison (C++20) 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) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)    is_eqis_neqis_ltis_lteqis_gtis_gteq (C++20)(C++20)(C++20)(C++20)(C++20)(C++20)

General utilities Date and time Function objects Formatting library (C++20) 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 and type 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) Elementary string conversions to_chars (C++17) from_chars (C++17) chars_format (C++17)

 

Function objects

Function wrappers function (C++11) move_only_function (C++23) 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)

 

Defined in header <functional>
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 << "° = " << f1(n) << " rad (using binder) "
                                 << f2(n) << " rad (using lambda)\n";
}

Output:

0° = 0 rad (using binder) 0 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° = 1.0472 rad (using binder) 1.0472 rad (using lambda)
90° = 1.5708 rad (using binder) 1.5708 rad (using lambda)
180° = 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)