Home Original page

std::function<R(Args...)>::operator() - cppreference.com

From cppreference.com

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.

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

Throws 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 be passed to other functions by value. Also, it shows how std::function can store lambdas.

#include <functional>
#include <iostream>

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;
    try
    {
        call(f);
    }
    catch (const std::bad_function_call& ex)
    {
        std::cout << ex.what() << '\n';
    }

    f = [&n](){ return n; };
    call(f);

    n = 2;
    call(f);

    f = normal_function;
    call(f);

    std::function<void(std::string, int)> g;
    g = [](std::string str, int i) { std::cout << str << ' ' << i << '\n'; };
    g("Hi", 052);
}

Possible output: 

bad_function_call
1
2
42
Hi 42

See also

invokes the target
(public member function of std::move_only_function) [edit]
calls the stored function
(public member function of std::reference_wrapper<T>) [edit]
the exception thrown when invoking an empty std::function
(class) [edit]
invokes any Callable object with given arguments and possibility to specify return type(since C++23)
(function template) [edit]