How To Implement Timer in C

[UG]

I just wanted to know whether any timer facility exists in C, as it is
not mentioned in K&R 2, or in the ISO Draft. By timer function i mean
that when we use standard input function like scanf() or getch() or
any other function, the interface stops to take input from user but
what if user doesn't give input for hours, the program will still be
waiting. Is there any way to circumvent the scanf() (or any other
input function for that matter) so that it takes some default input or
no input and just proceeds to the next line of the execution assuming
input from user as nothing and acts accordingly.

[Ian Collins]

UG wrote:

I just wanted to know whether any timer facility exists in C, as it is
not mentioned in K&R 2, or in the ISO Draft. By timer function i mean
that when we use standard input function like scanf() or getch() or
any other function, the interface stops to take input from user but
what if user doesn't give input for hours, the program will still be
waiting. Is there any way to circumvent the scanf() (or any other
input function for that matter) so that it takes some default input or
no input and just proceeds to the next line of the execution assuming
input from user as nothing and acts accordingly.

Not in standard C, but it may be possible on your target platform, so
try asking on a group for that environment.

--
Ian Collins.

[Nelu]

UG wrote:

I just wanted to know whether any timer facility exists in C, as it is
not mentioned in K&R 2, or in the ISO Draft.

No.

<snip>

Is there any way to circumvent the scanf() (or any other
input function for that matter) so that it takes some default input or
no input and just proceeds to the next line of the execution assuming
input from user as nothing and acts accordingly.

I assume it uses the default value on time out. Still, the answer
is no.

You may want to look into either threads or processes but none of
them is topical here.

--
Ioan - Ciprian Tandau
tandau _at_ freeshell _dot_ org (hope it's not too late)
(... and that it still works...)

[user923005]

On Feb 27, 9:15 pm, "UG" <unmeshgh...@gm ail.comwrote:

I just wanted to know whether any timer facility exists in C, as it is
not mentioned in K&R 2, or in the ISO Draft. By timer function i mean
that when we use standard input function like scanf() or getch() or
any other function, the interface stops to take input from user but
what if user doesn't give input for hours, the program will still be
waiting. Is there any way to circumvent the scanf() (or any other
input function for that matter) so that it takes some default input or
no input and just proceeds to the next line of the execution assuming
input from user as nothing and acts accordingly.

>From the C-FAQ:

19.37: How can I implement a delay, or time a user's response, with
sub-
second resolution?

A: Unfortunately, there is no portable way. V7 Unix, and derived
systems, provided a fairly useful ftime() function with
resolution up to a millisecond, but it has disappeared from
System V and POSIX. Other routines you might look for on your
system include clock(), delay(), gettimeofday(), msleep(),
nap(), napms(), nanosleep(), setitimer(), sleep(), times(), and
usleep(). (A function called wait(), however, is at least under
Unix *not* what you want.) The select() and poll() calls (if
available) can be pressed into service to implement simple
delays. On MS-DOS machines, it is possible to reprogram the
system timer and timer interrupts.

Of these, only clock() is part of the ANSI Standard. The
difference between two calls to clock() gives elapsed execution
time, and may even have subsecond resolution, if CLOCKS_PER_SEC
is greater than 1. However, clock() gives elapsed processor time
used by the current program, which on a multitasking system may
differ considerably from real time.

If you're trying to implement a delay and all you have available
is a time-reporting function, you can implement a CPU-intensive
busy-wait, but this is only an option on a single-user, single-
tasking machine as it is terribly antisocial to any other
processes. Under a multitasking operating system, be sure to
use a call which puts your process to sleep for the duration,
such as sleep() or select(), or pause() in conjunction with
alarm() or setitimer().

For really brief delays, it's tempting to use a do-nothing loop
like

long int i;
for(i = 0; i < 1000000; i++)
;

but resist this temptation if at all possible! For one thing,
your carefully-calculated delay loops will stop working properly
next month when a faster processor comes out. Perhaps worse, a
clever compiler may notice that the loop does nothing and
optimize it away completely.

References: H&S Sec. 18.1 pp. 398-9; PCS Sec. 12 pp. 197-8,215-
6; POSIX Sec. 4.5.2.

[yunyuaner]

On 2ÔÂ28ÈÕ, ÏÂÎç1ʱ15·Ö, "UG" <unmeshgh...@gm ail.comwrote:

I just wanted to know whether any timer facility exists in C, as it is
not mentioned in K&R 2, or in the ISO Draft. By timer function i mean
that when we use standard input function like scanf() or getch() or
any other function, the interface stops to take input from user but
what if user doesn't give input for hours, the program will still be
waiting. Is there any way to circumvent the scanf() (or any other
input function for that matter) so that it takes some default input or
no input and just proceeds to the next line of the execution assuming
input from user as nothing and acts accordingly.

The above description is clear.
Many platforms provide timer, such as win32, in which you can use func
settimer
Anyway, there is a poor implementation of timer in linux
void sig_alrm(int signo)
{
return;
}

int main()
{
signal(SIGARLM, sig_alrm);
alarm(1);
scanf(...);
/* time up, your can capture the signal by checking errno */
return 0;
}

[mark_bluemel]

On Feb 28, 9:33 am, "yunyua...@gmai l.com" <yunyua...@gmai l.comwrote:

On 2月28日, 下�1时15分 , "UG" <unmeshgh...@gm ail.comwrote:

I just wanted to know whether any timer facility exists in C, as it is
not mentioned in K&R 2, or in the ISO Draft. By timer function i mean
that when we use standard input function like scanf() or getch() or
any other function, the interface stops to take input from user but
what if user doesn't give input for hours, the program will still be
waiting. Is there any way to circumvent the scanf() (or any other
input function for that matter) so that it takes some default input or
no input and just proceeds to the next line of the execution assuming
input from user as nothing and acts accordingly.

The above description is clear.
Many platforms provide timer, such as win32, in which you can use func
settimer
Anyway, there is a poor implementation of timer in linux
void sig_alrm(int signo)
{
return;

}

int main()
{
signal(SIGARLM, sig_alrm);
alarm(1);
scanf(...);
/* time up, your can capture the signal by checking errno */
return 0;

}

<OffTopic>

The usual method I've seen for this sort of thing is to use either
select() or poll(), neither of which are part of the C standard, but
are common on Unix-like platforms.

Much better than the alarm-based approach, IMHO.

</Offtopic>

[Kenny McCormack]

In article <54************ *@mid.individua l.net>,
Ian Collins <ia******@hotma il.comwrote:

>UG wrote:

>I just wanted to know whether any timer facility exists in C, as it is
not mentioned in K&R 2, or in the ISO Draft. By timer function i mean
that when we use standard input function like scanf() or getch() or
any other function, the interface stops to take input from user but
what if user doesn't give input for hours, the program will still be
waiting. Is there any way to circumvent the scanf() (or any other
input function for that matter) so that it takes some default input or
no input and just proceeds to the next line of the execution assuming
input from user as nothing and acts accordingly.

Not in standard C, but it may be possible on your target platform, so
try asking on a group for that environment.

IOW:

Off topic. Not portable. Cant discuss it here. Blah, blah, blah.

Useful clc-related links:

http://en.wikipedia.org/wiki/Aspergers
http://en.wikipedia.org/wiki/Clique
http://en.wikipedia.org/wiki/C_programming_language

[achiever]

On Feb 27, 9:15 pm, "UG" <unmeshgh...@gm ail.comwrote:

I just wanted to know whether any timer facility exists in C, as it is
not mentioned in K&R 2, or in the ISO Draft. By timer function i mean
that when we use standard input function like scanf() or getch() or
any other function, the interface stops to take input from user but
what if user doesn't give input for hours, the program will still be
waiting. Is there any way to circumvent the scanf() (or any other
input function for that matter) so that it takes some default input or
no input and just proceeds to the next line of the execution assuming
input from user as nothing and acts accordingly.

yes their exists a time delaying facility under c
the
*delay()* function which delay the output on the the screen
by
the time of declared in side bracesthis function is defined in dos.h
header file

[mark_bluemel]

On Feb 28, 4:08 pm, "achiever" <friends.vik... @gmail.comwrote :

On Feb 27, 9:15 pm, "UG" <unmeshgh...@gm ail.comwrote:

I just wanted to know whether any timer facility exists in C, as it is
not mentioned in K&R 2, or in the ISO Draft. By timer function i mean
that when we use standard input function like scanf() or getch() or
any other function, the interface stops to take input from user but
what if user doesn't give input for hours, the program will still be
waiting. Is there any way to circumvent the scanf() (or any other
input function for that matter) so that it takes some default input or
no input and just proceeds to the next line of the execution assuming
input from user as nothing and acts accordingly.

yes their exists a time delaying facility under c
the
*delay()* function which delay the output on the the screen
by
the time of declared in side bracesthis function is defined in dos.h
header file

Which on my conforming C implementations is sadly missing. Should I
complain to the suppliers?

[Richard Bos]

"achiever" <fr************ @gmail.comwrote :

On Feb 27, 9:15 pm, "UG" <unmeshgh...@gm ail.comwrote:

I just wanted to know whether any timer facility exists in C, as it is
not mentioned in K&R 2, or in the ISO Draft. By timer function i mean
that when we use standard input function like scanf() or getch() or
any other function, the interface stops to take input from user but
what if user doesn't give input for hours, the program will still be
waiting. Is there any way to circumvent the scanf() (or any other
input function for that matter) so that it takes some default input or
no input and just proceeds to the next line of the execution assuming
input from user as nothing and acts accordingly.

yes their exists a time delaying facility under c

No, there doesn't.

the *delay()* function which delay the output on the the screen

....does not exist in C.

the time of declared in side bracesthis function is defined in dos.h

....which also does not exist in C.

Your toy compiler may include it, but that doesn't mean it will work on
a real computer. Especially when it's called "dos.h".

Richard