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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; }

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; }