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std::future::valid(3)	       C++ Standard Libary	   std::future::valid(3)

NAME
     std::future::valid - std::future::valid

Synopsis
	bool valid() const noexcept;  (since C++11)

	Checks if the future refers to a shared state.

	This  is  the case only for futures that were not default-constructed or
     moved from
	(i.e.	  returned     by     std::promise::get_future(),     std::pack-
     aged_task::get_future() or
	std::async()) until the first time get() or share() is called.

	The behavior is undefined if any member function other than the destruc-
     tor, the
	move-assignment  operator,  or valid is called on a future that does not
     refer to
	shared state (although implementations are encouraged to throw	std::fu-
     ture_error
	indicating no_state in this case). It is valid to move from a future ob-
     ject for
	which valid() is false.

Parameters
	(none)

Return value
	true if *this refers to a shared state, otherwise false.

Example
     // Run this code

      #include <future>
      #include <iostream>

      int main()
      {
	  std::promise<void> p;
	  std::future<void> f = p.get_future();

	  std::cout << std::boolalpha;

	  std::cout << f.valid() << '\n';
	  p.set_value();
	  std::cout << f.valid() << '\n';
	  f.get();
	  std::cout << f.valid() << '\n';
      }

Output:
      true
      true
      false

See also
	wait waits for the result to become available
	     (public member function)

http://cppreference.com 	   2024.06.10		   std::future::valid(3)
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