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

R operator()( Args... args ) const;

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

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

#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);
}

1
2
42

See also