Hi everybody,
I am awfully new to programming in C and all I have had to work with
so far have been tutorials that I've found online. In my searching,
however, I have not found a solution to a problem I have been facing.
Ideally, I would like the program to wait 5 minutes before executing
the rest of the code. Is there some way that I can use time.h and just
run a for loop that waits until 5 minutes has passed to continue down
the program?
Any help that you experts could give would be greatly appreciated.
Also, I apologize in advance if there is an obvious solution I have
overlooked.
The obvious solution that you overlooked was to read 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. Routines you might
look for on your system include clock(), delay(), ftime(),
gettimeofday(), msleep(), nap(), napms(), nanosleep(),
setitimer(), sleep(), 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.
