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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_REALTIME
to 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;
}