When to use fflush()?

[Doug Gwyn]

In article <143 at sherpa.uucp> rac at sherpa.uucp (Roger A. Cornelius) writes:
>When should you use fflush()? OR are there any guarantees of
>when output buffers are flushed?

Use fflush() whenever you want to make sure that the buffers are forced out.

>I have a program that uses fputs() to print a prompt, then waits for a
>return to be typed.  The prompt is always displayed, but am I guaranteed
>of this?

Recent versions of stdio attempt to force out all output possibly associated
with a "terminal" whenever input is requested from a "terminal".  It is not
always possible to tell what is really a terminal, though.  Modern stdio
also defaults to line-buffered output on "terminals", although that wouldn't
help for a prompt on the same line as the input.

>Should I use fflush() anyway?  What's the rule for when to use
>fflush(), and when it's not needed?

See my first sentence.