operator==,!=(std::function)

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Compiler support
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Language
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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std::function

Member functions
function::function
function::~function
function::operator=
function::swap
function::assign (until C++17)
function::operator bool
function::operator()
function::target_type
function::target
Non-member functions
operator==operator!= (until C++20)
swap(std::function)
Helper classes
uses_allocator<std::function> (until C++17)
Deduction guides(C++17)

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Defined in header`<functional>`
template<class R,class...ArgTypes> bool operator==(conststd::function<R(ArgTypes...)>& f, std::nullptr_t)noexcept;	(1)	(since C++11)
template<class R,class...ArgTypes> bool operator==(std::nullptr_t, conststd::function<R(ArgTypes...)>& f)noexcept;	(2)	(since C++11) (until C++20)
template<class R,class...ArgTypes> bool operator!=(conststd::function<R(ArgTypes...)>& f, std::nullptr_t)noexcept;	(3)	(since C++11) (until C++20)
template<class R,class...ArgTypes> bool operator!=(std::nullptr_t, conststd::function<R(ArgTypes...)>& f)noexcept;	(4)	(since C++11) (until C++20)

Compares astd::function with a null pointer. Empty functions (that is, functions without a callable target) compare equal, non-empty functions compare non-equal.

The!= operator issynthesized fromoperator==.

(since C++20)

[edit]Parameters

f - std::function to compare

[edit]Return value

1,2)!f

3,4)(bool) f

[edit]Example

Run this code

#include <functional>#include <iostream> using SomeVoidFunc=std::function<void(int)>; class C{public:    C(SomeVoidFunc void_func= nullptr): void_func_(void_func){if(void_func_== nullptr)// specialized compare with nullptr            void_func_=std::bind(&C::default_func, this, std::placeholders::_1);        void_func_(7);} void default_func(int i){std::cout<< i<<'\n';}; private:    SomeVoidFunc void_func_;}; void user_func(int i){std::cout<<(i+1)<<'\n';} int main(){    C c1;    C c2(user_func);}