question on select.

question on select.

[Lejanson C. Go]

hello good day.
i have a question about the select()
function.

when should we set timeout parameter
into NULL? what is the difference of
putting timeout (0, 0) OR putting NULL
as parameter?

--
while(1) {
   tv.sec = 0;
   tv.usec = 0;
   sel = select(fd+1, &rdfd, NULL, NULL, &tv);
}
--
--
while(1) {
   sel = select(fd+1, &rdfd, NULL, NULL, NULL);
}
--

thanks a lot.


lejanson

Re: question on select.

[Glynn Clements]

Lejanson C. Go wrote:

> i have a question about the select()
> function.
> 
> when should we set timeout parameter
> into NULL? what is the difference of
> putting timeout (0, 0) OR putting NULL
> as parameter?

Passing NULL for the timeout parameter will cause select() to wait
indefinitely. It won't return until either one of the descriptors is
ready or it's interrupted by a signal. The return value will never be
zero (it will return a positive value if a descriptor is ready or -1
if it is interrupted).

Passing a pointer to a zero interval (tv_sec == tv_usec == 0) will
cause select() to return immediately, even if no descriptors are ready
(in which case, the return value will be zero and all of the
descriptor sets will be empty).

-- 
Glynn Clements <glynn.clements@virgin.net>