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std::promis...et_exception(3)  C++ Standard Libary std::promis...et_exception(3)

NAME
     std::promise::set_exception - std::promise::set_exception

Synopsis
	void set_exception( std::exception_ptr p );  (since C++11)

	Atomically  stores  the  exception  pointer  p into the shared state and
     makes the state
	ready.

	The   operation   behaves   as	  though    set_value,	  set_exception,
     set_value_at_thread_exit,
	and  set_exception_at_thread_exit acquire a single mutex associated with
     the promise
	object while updating the promise object.

	An exception is thrown if there is no shared state or the  shared  state
     already
	stores a value or exception.

	Calls to this function do not introduce data races with calls to get_fu-
     ture
	(therefore they need not synchronize with each other).

Parameters
	p - exception pointer to store. The behavior is undefined if p is null

Return value
	(none)

Exceptions
	std::future_error on the following conditions:

	  * *this has no shared state. The error code is set to no_state.
	  * The shared state already stores a value or exception. The error code
     is set to
	    promise_already_satisfied.

Example
     // Run this code

      #include <future>
      #include <iostream>
      #include <thread>

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

	  std::thread t([&p]
	  {
	      try
	      {
		  // code that may throw
		  throw std::runtime_error("Example");
	      }
	      catch (...)
	      {
		  try
		  {
		      // store anything thrown in the promise
		      p.set_exception(std::current_exception());
		      // or throw a custom exception instead
		      //	p.set_exception(std::make_exception_ptr(MyExcep-
     tion("mine")));
		  }
		  catch (...) {} // set_exception() may throw too
	      }
	  });

	  try
	  {
	      std::cout << f.get();
	  }
	  catch (const std::exception& e)
	  {
	      std::cout << "Exception from the thread: " << e.what() << '\n';
	  }
	  t.join();
      }

Output:
      Exception from the thread: Example

See also
				     sets the result to  indicate  an  exception
     while
	set_exception_at_thread_exit  delivering the notification only at thread
     exit
				     (public member function)

http://cppreference.com 	   2024.06.10	   std::promis...et_exception(3)
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