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std::basic_ostream::flush(3)   C++ Standard Libary  std::basic_ostream::flush(3)

NAME
     std::basic_ostream::flush - std::basic_ostream::flush

Synopsis
	basic_ostream& flush();

	Writes uncommitted changes to the underlying output sequence. Behaves as
     an
	UnformattedOutputFunction.

	If rdbuf() is a null pointer, the sentry object is not constructed.

	Otherwise, after constructing and checking the sentry object, calls
	rdbuf()->pubsync(). If the call returns -1, calls setstate(badbit).

Parameters
	(none)

Return value
	*this

Exceptions
	May throw std::ios_base::failure if (exceptions() & badbit) != 0.

Example
     // Run this code

      #include <chrono>
      #include <iostream>
      #include <thread>

      using namespace std::chrono_literals;

      void f()
      {
	  std::cout << "Output from thread... ";
	  for (int i{1}; i != 10; ++i)
	  {
	      std::this_thread::sleep_for(250ms);
	      std::cout << i << ' ';

	      // output three numbers at once;
	      // the effect is observable only in real-time
	      if (0 == (i % 3))
		  std::cout.flush();
	  }
	  std::cout << std::endl; // flushes as well
      }

      int main()
      {
	  std::thread tr{f};
	  std::this_thread::sleep_for(150ms);
	  std::clog << "Output from main\n";
	  tr.join();
      }

Output:
      Output from main
      Output from thread... 1 2 3 4 5 6 7 8 9

	Defect reports

	The  following	behavior-changing  defect  reports were applied retroac-
     tively to
	previously published C++ standards.

	  DR	Applied to	    Behavior as  published		 Correct
     behavior
			   flush() did not behave as an
	LWG 581 C++98	   UnformattedOutputFunction		   behaves as an
			   because  of the resolution of LWG issue  Unformatted-
     OutputFunction
			   60

See also
	pubsync   invokes sync()
		  (public member function of std::basic_streambuf<CharT,Traits>)
	sync	  synchronizes the buffers with  the  associated  character  se-
     quence
	[virtual]  (virtual  protected	member	function  of  std::basic_stream-
     buf<CharT,Traits>)

	flush	  flushes the output stream
		  (function template)
	endl	  outputs '\n' and flushes the output stream
		  (function template)
	sync	  synchronizes with the underlying storage device
		  (public member function of std::basic_istream<CharT,Traits>)

http://cppreference.com 	   2024.06.10	    std::basic_ostream::flush(3)
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