Result of time() not updated after sleep()

March 18, 2022

I’m trying to pause my program for 1 second, and check the system time after that (I’m on Linux)

This is my testing program:

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

int main() {

    time_t now = time(NULL);
    struct tm *time_now = localtime(&now);
    printf("now: %d-%d\n", time_now->tm_min, time_now->tm_sec);

    int i = 0;
    for (; i < 5; i++) {
        sleep(1);
    }
    // This printf result is not as expected
    printf("now: %d-%d\n", time_now->tm_min, time_now->tm_sec);

    return 0;
}

The expected result is that the second printf would print +5 seconds. Instead, it prints the same time/seconds as the first printf.

I’ve found (maybe) the same problem posted here, but it doesn’t seem to work:
sleep() and time() not functioning as expected inside for loop.

Sorry for my bad english, and thank you for your time.

>Solution :

Code is printing the original *time_now values – as expected.

Simply read time again to use new values.

time_t now = time(NULL);
struct tm *time_now = localtime(&now);
printf("now: %d-%d\n", time_now->tm_min, time_now->tm_sec);

int i = 0;
for (; i < 5; i++) {
    sleep(1);
}

// Add
time_t now = time(NULL);
struct tm *time_now = localtime(&now);

printf("now: %d-%d\n", time_now->tm_min, time_now->tm_sec);