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

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 = [&n](){ return n; };
    call(f);
 
    n = 2;
    call(f);
 
    f = normal_function;
    call(f);
}

Output:

1
2
42

See also

(C++23)
 invokes the target
(public member function of std::move_only_function)
calls the stored function
(public member function of std::reference_wrapper<T>)
(C++11)
 the exception thrown when invoking an empty std::function
(class)
(C++17)(C++23)
 invokes any Callable object with given arguments and possibility to specify return type (since C++23)
(function template)

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