BOOST threading : cout behavior
boost, boost-thread, c++
Solution
This isn't specifically thread related as cout will buffer usually on a per thread basis and only output when the implementation decides to - so in the thread the output will only appear on a implementation specific basic - by calling flush you are forcing the buffers to be flushed.
This will vary across implementations - usually though it's after a certain amount of characters or when a new line is sent.
I've found that multiple threads writing too the same stream or file is mostly OK - providing that the output is performed as atomically as possible. It's not something that I'd recommend in a production environment though as it is too unpredictable.
Problem
I am new to Boost threading and I am stuck with how output is performed from multiple threads. I have a simple boost::thread counting down from 9 to 1; the main thread waits and then prints "LiftOff..!!" ``` #include <iostream> #include <boost/thread.hpp> using namespace std; struct callable { void operator() (); }; void callable::operator() () { int i = 10; while(--i > 0) { cout << "#" << i << ", "; boost::this_thread::yield(); } cout.flush(); } int main() { callable x; boost::thread myThread(x); myThread.join(); cout << "LiftOff..!!" << endl; return 0; } ``` The problem is that I have to use an explicit "cout.flush()" statement in my thread to display the output. If I don't use flush(), I only get "LiftOff!!" as the output. Could someone please advise why I need to use flush() explicitly?