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std::promis...et_exception(3) C++ Standard Libarystd::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_future
	  (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 <thread>
	#include <iostream>
	#include <future>

	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	excep-
       tion while
	  set_exception_at_thread_exit	delivering  the	 notification  only at
       thread exit
				       (public member function)

http://cppreference.com		  2022.07.31	 std::promis...et_exception(3)

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