How do I delay a function in C?

Question

I can't find a viable guide so I am asking how do I delay a function in C, in other words, how do I make a program wait a certain number of seconds before continuing to execute other functions?

For example:

printf("First Function.\n");

//program waits a certain number of seconds before executing next command

printf("Second function executed after certain amount of seconds");

I want to know, what is the command I use to make this happen?

delay();

for me doesn't work by the way.

I must add, sleep() doesn't work either.

There is no such capability in standard C. Solutions are specific to operating systems (or families of operating systems). For example, `sleep()` under unix, `Sleep()` under windows. You'll need to read the documentation for your target system and associated APIs. — Peter, Apr 29 '17 at 14:21
"*`sleep()` doesn't work either.*" does not work in which sense? Please be more specific! On which platform are you experiencing these issues? — alk, Apr 29 '17 at 15:39
This question is related to this question http://stackoverflow.com/q/14812233/694576 if not a duplicate to it. — alk, Apr 29 '17 at 16:59
@alk: Despite your 'not a duplicate' comment, I think it is covering exactly the same territory, and so I've made it a duplicate. Whole-second vs sub-second sleeping is still sleeping. — Jonathan Leffler, Jun 11 '17 at 00:54

score 7 · Answer 1 · answered Apr 29 '17 at 14:15

7

sleep is what you’re looking for.

printf("First Function.\n");

sleep(20);  // Replace 20 with the "certain amount"

printf("Second function executed after certain amount of seconds")

answered Apr 29 '17 at 14:15

idmean

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The latest documentation is here; http://pubs.opengroup.org/onlinepubs/9699919799/utilities/sleep.html – alk Apr 30 '17 at 04:58

Pras · Answer 2 · 2017-04-29T14:23:54.457

1

You can use Sleep() or select to add delay.

edited Apr 29 '17 at 14:23

answered Apr 29 '17 at 14:15

Pras

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I am curious why `sleep()` wouldn't be thread-safe. – Dolda2000 Apr 29 '17 at 14:17
I edited my answer, I dont know why but I am just used to call select for delays in threads, documentation for sleep clearly says only calling thread sleeps – Pras Apr 29 '17 at 14:24
Perhaps you were thinking of `pselect()`, which has nothing with thread-safety to do, but is async-signal safe. – Dolda2000 Apr 29 '17 at 14:25

ad absurdum · Answer 3 · 2017-04-30T09:22:52.023

1

The sleep() function is POSIX. There is also the POSIX function nanosleep() if more precision is needed.

There is the thrd_sleep() function in C11 (from threads.h), but AFAIK this function is still not supported by glibc.

A simple sleep function could be implemented portably using the functions from time.h:

#include <stdio.h>
#include <time.h>

void my_sleep(unsigned);
void delay_print(char *);

int main(void)
{
    delay_print("What is taking so long?");
    delay_print("Glad that's over!");
}

void my_sleep(unsigned duration)
{
    time_t start = time(NULL);
    double end = duration;
    time_t now;
    do {
        now = time(NULL);
    } while (difftime(now, start) < end);
}

void delay_print(char *msg)
{
    my_sleep(5);
    puts(msg);
}

edited Apr 30 '17 at 09:22

answered Apr 29 '17 at 16:49

ad absurdum

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this sucks all the available CPU cycles due to the 'polling', so probably not the best approach. – user3629249 Apr 30 '17 at 18:03
@user3629249-- I did write "simple sleep function," and I think that it was implicit in my answer that this could be used in the _absence_ of any appropriate library functions. I think that most OS will detect the load and make adjustments. I am not sure that there is a portable way to do this and avoid CPU overhead, but I would be happy to see an alternative :) – ad absurdum Apr 30 '17 at 18:39
Conflictingly. I have minGW on windows 11 and eclipse findng `Sleep(10);` on `synchapi.h` and `sleep(10);` on `unistd.h`, why? – mohammadsdtmnd Nov 15 '22 at 18:51
@mohammadsdtmnd -- I don't understand "_conflictingly_". `synchapi.h` is a Windows-only header which declares a `Sleep` function; `unistd.h` is the Posix header that declares `sleep`. You can have both on the same system. – ad absurdum Nov 15 '22 at 19:56

score 0 · Answer 4 · edited Apr 30 '17 at 09:50

0

You can easily use:

sleep(unsigned int seconds);   //   from the unistid.h
Sleep(int milliseconds);       //   from the Windows.h

edited Apr 30 '17 at 09:50

phuclv

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answered Apr 29 '17 at 21:30

Fabio La Greca

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POSIX's `sleep()` takes an `unsigned int`. – alk Apr 30 '17 at 04:56

How do I delay a function in C?

4 Answers4