Question

How can you get unbuffered output from cout, so that it instantly writes to the console without the need to flush (similar to cerr)?

I thought it could be done through rdbuf()->pubsetbuf, but this doesn’t seem to work. The following code snippet below is supposed to immediately output to the console, and then wait a few seconds. But instead, it just waits, and only outputs when the program exits and the buffer is flushed.

#include <iostream>

int main()
{
        std::cout.rdbuf()->pubsetbuf(0, 0);
        std::cout << "A";
        sleep(5);
}

Answer 1

You can set the std::ios_base::unitbuf flag to flush output after each output operation either by calling std::ios_base::setf:

std::cout.setf(std::ios::unitbuf);

or using the std::unitbuf manipulator:

std::cout << std::unitbuf;