Again, is cout buffered or unbuffered ?

Question

On this thread it was shown that cout is unbuffered when directed to the console. However when I run this code I get that the default value for the std::ios_base::unitbuf flag for the stream cout is unset, which says the contrary, i.e., that cout is buffered.

#include <iostream>

int main()
{
	// This prints "unset" for the default value of the flag
        // std::ios_base::unitbuf for the stream cout
	
	std::cout << "Flag unitbuf " <<
            (std::cout.flags() & std::ios_base::unitbuf ? "set" : "unset") << '\n';
}

 

Answer 1

On 1/22/2013 1:21 PM, Ayrosa wrote:

On this thread <http://social.msdn.microsoft.com/Forums/en-US/vclanguage/thread/415aac5f-0bf1-4ad1-a673-597ac042d36f> it was shown that cout is unbuffered when directed to the console. However when I run this code I get that the default value for the std::ios_base::unitbuf flag for the stream/cout/ is /unset/, which says the contrary, i.e., that /cout/ is buffered.

unitbuf flag controls whether the buffer is flushed after each output operation. As such, it only affects buffered streams - if there's no buffer, there's nothing to flush. This is similar to how the output of printf() appears on the console immediately, without you having to call fflush(stdout).

---

Igor Tandetnik

Answer 2

>Again, is cout buffered or unbuffered ?

You were given the definitive answer in the other
thread from the Microsoft employee who maintains
the Standard Library and iostreams.

- Wayne

Answer 3

WayneAKing wrote:

You were given the definitive answer in the other
thread from the Microsoft employee who maintains
the Standard Library and iostreams.

The problem Wayne is that MS own docs contradict what Mr. Lavavej said. But I have no more doubts in my mind that cout is unbuffered ! Thanks.