std::function<R(Args...)>::operator() (3) - Linux Man Pages

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

NAME

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

Synopsis


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


                  calls the stored function
operator() (public member function of std::reference_wrapper<T>)


bad_function_call the exception thrown when invoking an empty std::function
                  (class)
(C++11)


invoke invokes any Callable object with given arguments
                  (function template)
(C++17)