Checking for waiting characters

[Doug Gwyn]

In article <1364 at ihuxy.UUCP> ejbjr at ihuxy.UUCP (Branagon) writes:
>> In article <470 at brl-smoke.ARPA> KEN%NJITCCCC.BITNET at wiscvm.wisc.edu (Kenneth Ng) writes:
>> >On Unix System V version 2 on an AT&T 3b5, has anyone been able to
>> >successfully test if characters are pending?  I've got an application
>> >that needs to time out after a certain amount of time if no characters
>> >come through.
>
>The easiest way I've found to do this is to set an alarm, and use a signal
>trapping function (see alarm(2) and signal(2)).  The alarm can be set once
>at the beginning, or reset after each character.  I'm not sure if alarm()
>is sysV specific or not.

No, alarm() has been in all UNIXes since 6th Edition.
However, the alarm signal can mangle I/O involving "slow"
devices (typically terminal ports), so it is not suitable
for some applications like this.  Other approaches such
as using MIN,TIME are preferable.