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

int main() {
    struct timespec ts = {0};
    struct tm tm = {0};

    for (;;) {
        // print time
        clock_gettime(CLOCK_REALTIME, &ts);
        localtime_r(&ts.tv_sec, &tm);
        printf("%s", asctime(&tm));
        fflush(stdout);

        // delay until next second
        struct timespec td = {
            .tv_sec = 0,
            .tv_nsec = 1000000000 - ts.tv_nsec,
        };

        nanosleep(&td, NULL);
    }

    return 0;
}