Time acquisition function

The basic time provided by the Linux kernel since this particular time 1970-01-01 00:00:00 +0000 (UTC) after a number of seconds, this description is based on data type time_t representation, which we call the calendar time.
Function to get the calendar time there are three: time, clock_gettime and gettimeofday.

time function

#include <time.h>

//成功返回日历时间，出错返回-1；若time非NULL，则也通过其返回时间值
time_t time(time_t *time);

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

void print_time()
{
    time_t seconds = time(NULL);

    printf("seconds = %ld\n", seconds);
}

int main()
{
    print_time();

    return 0;
}

clock_gettime function

clock_gettime function obtains a specified clock time, return time saved by struct timespec structure, the structure and the time is expressed in seconds nanoseconds.

#include <time.h>

struct timespec
{
    time_t   tv_sec;        /* seconds */
    long     tv_nsec;       /* nanoseconds */
};

//Link with -lrt.
int clock_gettime(clockid_t clock_id, struct timespec *tsp);

clock_id generally set CLOCK_REALTIMEto obtain a high precision calendar time.

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

void print_time()
{
    time_t seconds;
    struct timespec tsp;

    seconds = time(NULL);
    printf("seconds = %ld\n", seconds);

    clock_gettime(CLOCK_REALTIME, &tsp);
    printf("tsp.tv_sec = %ld, tsp.tv_nsec = %ld\n", tsp.tv_sec, tsp.tv_nsec);
}

int main()
{
    print_time();

    return 0;
}

gettimeofday function

Clock_gettime functions and the like, by the gettimeofday returns calendar time struct timeval structure that the time is expressed in seconds and subtle.

#include <sys/time.h>

struct timeval
{
    time_t      tv_sec;     /* seconds */
    suseconds_t tv_usec;    /* microseconds */
};

int gettimeofday(struct timeval *tv, struct timezone *tz);

It should be noted that the only legitimate tz parameter value is NULL.

#include <stdio.h>
#include <string.h>
#include <time.h>
#include <sys/time.h>

void print_time()
{
    time_t seconds;
    struct timespec tsp;
    struct timeval tv;

    seconds = time(NULL);
    printf("seconds = %ld\n", seconds);

    clock_gettime(CLOCK_REALTIME, &tsp);
    printf("tsp.tv_sec = %ld, tsp.tv_nsec = %ld\n", tsp.tv_sec, tsp.tv_nsec);

    gettimeofday(&tv, NULL);
    printf("tv.tv_sec = %ld, tv.tv_usec = %ld\n", tv.tv_sec, tv.tv_usec);
}

int main()
{
    print_time();

    return 0;
}