Date: Tue, 22 Jul 1997 22:09:10 -0700 From: Paul Traina <pst@shockwave.com> To: hackers@freebsd.org Subject: how to tell if getchar() will block -- select doesn't cut it Message-ID: <199707230509.WAA13342@precipice.shockwave.com>
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I had some fun this week -- I'd added some asynchronous event code to a
little line editor so that I could deal with some events while waiting
from user input...
The code looked something like:
<select cruft to wait on several sockets>
if (read data available on stdin) {
c = getchar();
go do more processing;
}
This worked fine and dandy except that pasting into a window running this
program didn't work properly -- characters seemed to get lost.
The obvious problem is that the paste was sending down many characters,
stdio read more than one character and stored it in a local buffer, so
there was data available for getchar(), but of course, the low level buffer
had already been slurped in, so the select wasn't returning true.
I worked around this by checking, in a non-portable fashion, if stdio had
any data available for it (if (fp->_r >= 0 || fp->_ur >= 0)) but quite
frankly, non-portable code sucks.
I did a reasonable perusal of the source code in stdio and I can't seem
to find any portable way to ask the general question:
Is getchar() going to block if I call it?
Ideas?
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