windows - Disable buffering on redirected stdout Pipe (Win32 API, C++)

Question

I'm spawning a process from Win32 using CreateProcess, setting the hStdOutput and hStdError properties of STARTUPINFO to pipe handles created with CreatePipe. I've got two threads reading the pipes, waiting for data to become available (or the process to complete, at which point it checks that there is no data left before terminating the thread).
As data becomes available, I write the output out to effectively a big textbox.

What's happening is the output is being buffered, so a slow running process just gets chunks of data thrown at the text box, but not "as it happens".

I'm not sure if it's the pipe that's doing the buffering, or something to do with the redirection.

Is there any way to either set the pipe to be unbuffered, or start the process in such a way that the stdout is sent as soon as possible?

I'm testing with a test app that prints lines one second apart

Here is line one
(waits one second)
Here is line two
(waits one second)
... etc

Answer 1

The buffering is probably in the C runtime (printf etc) and there is not much you can do about it (IIRC it does a isatty() check to determine a buffering strategy)