std::function<R(Args...)>::operator()

 

C++

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Function objects

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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)

 

std::function

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function::operator=

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function::operator bool

function::operator()

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function::target

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operator==operator!=

std::swap(std::function)

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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<T>)
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)