[erpicci]

Sorry, I didn't see your point before.

If it didn't work then you're doing something wrong, because stderr is WRONG. stdout is proper... Did you test this through a debugger or actually run the program?

First I run it, using stdout; I saw it didn't work, so I tried through a debugger (gdb). Then I repeated using stderr.
Even through the debugger, the string is printed only at the end of the execution (when stdout is used).

I haven't tested how the carriage return works on a Unix system, I'd imagine it would be fine as long as the developers define the beginning of a line the same as in Windows or at least close enough to the same...

I think this is the case... otherwise the version using stderr wouldn't work at all, would it?

The issue is the Sleep() function; being a Windows only function in this case.[...]

I'm not sure: I tried to implement a CPU-eating function, without using "sleep" or any other thread/time function. Once again, it works using stderr but not with stdout.
That function is "compute the matrix product between A and B for 100 times, where A and B are both 100x100" (naive algorithm, no optimization, takes some milliseconds).

Now, I'm really curious to understand why this happens...