std::function::operator()

C++

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Named requirements

Language support library

Concepts library (C++20)

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Regular expressions library (C++11)

Atomic operations library (C++11)

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Technical Specifications

Utilities library

Type support (basic types, RTTI, type traits)
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bitset
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rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
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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
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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
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Function objects

Function wrappers function (C++11) mem_fn (C++11) bad_function_call (C++11)	Bind 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)
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)
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)

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!=

std::swap(std::function)

Helper classes

std::uses_allocator<std::function> (until C++17)

Deduction guides(C++17)

R operator()( Args... args ) const;		(since C++11)

Invokes the stored callable function target with the parameters args.

Effectively does INVOKE<R>(f, std::forward<Args>(args)...), where f is the target object of *this and INVOKE is the operation described in Callable.

Parameters

args

-

parameters to pass to the stored callable function target

Return value

None if R is void. Otherwise the return value of the invocation of the stored callable object.

Exceptions

• std::bad_function_call if *this does not store a callable function target, i.e. !*this == true.

Example

The following example shows how std::function can passed to other functions by value. Also, it shows how std::function can store lambdas.

Run this code

#include <iostream>
#include <functional>

void call(std::function<int()> f)  // can be passed by value
{ 
    std::cout << f() << '\n';
}

int normal_function() 
{
    return 42;
}

int main()
{
    int n = 1;
    std::function<int()> f = [&n](){ return n; };
    call(f);

    n = 2;
    call(f); 

    f = normal_function; 
    call(f);
}

Output:

1
2
42

See also

operator()	calls the stored function (public member function of std::reference_wrapper)
bad_function_call (C++11)	the exception thrown when invoking an empty std::function (class)
invoke (C++17)	invokes any Callable object with given arguments (function template)