clock_ gettime

function "clock_gettime" Is based on Linux C Time function of language , It can be used to calculate accuracy and nanoseconds .

externintclock_gettime (clockid_t __clock_id, structtimespec *__tp) __THROW;

__clock_id : Clock type ,posix The standard defines the following four basic types ,Linux The system has other extensions

1. CLOCK_REALTIME: System real time , It changes with the real time of the system , From UTC1970-1-1 0:0:0 Start timing , In the middle time, if the system time is changed by the user to other , The corresponding time will change accordingly .

2. CLOCK_MONOTONIC: Start timing from the moment the system starts , Not affected by the change of system time by users

3. CLOCK_PROCESS_CPUTIME_ID: This process to the current code system CPU Time spent . You need to pay attention to whether the time from the beginning of the process to the current code .

4. CLOCK_THREAD_CPUTIME_ID: This thread to the current code system CPU Time spent . You need to pay attention to whether the time from the beginning of the thread to the current code .

/* POSIX.1b structure for a time value.  This is like a `struct timeval' but
   has nanoseconds instead of microseconds.  */
struct timespec
{
    __time_t tv_sec;            /* Seconds.  */
    __syscall_s long_t tv_nsec;  /* Nanoseconds.  */
};

Sample code ：

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
 
int main(int argc,char *argv[])
{
    struct timespec time1 = {0};
 
    clock_gettime(CLOCK_REALTIME, &time1);
    printf("CLOCK_REALTIME: (%lu, %lu)\n", time1.tv_sec, time1.tv_nsec);
 
    clock_gettime(CLOCK_MONOTONIC, &time1);
    printf("CLOCK_MONOTONIC: (%lu, %lu)\n", time1.tv_sec, time1.tv_nsec);
 
    sleep(5);
    clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &time1);
    printf("CLOCK_PROCESS_CPUTIME_ID: (%lu, %lu)\n", time1.tv_sec, time1.tv_nsec);
 
    sleep(5);
    clock_gettime(CLOCK_THREAD_CPUTIME_ID, &time1);
    printf("CLOCK_THREAD_CPUTIME_ID: (%lu, %lu)\n", time1.tv_sec, time1.tv_nsec);
 
    printf("now time :%lu\n", time(NULL));
    return 0;
}

Running results ：

CLOCK_REALTIME: (1641541302, 670392667)
CLOCK_MONOTONIC: (280331, 989262689)
CLOCK_PROCESS_CPUTIME_ID: (0, 416834)
CLOCK_THREAD_CPUTIME_ID: (0, 436414)
now time :1641541312