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

typedef long     time_t;    /* 时间值time_t 为长整型的别名*/

#include <time.h>
time_t time(time_t *calptr);
                                    Returns: value of time if OK,?1 on error

 #include <time.h>
       int clock_getres(clockid_t clk_id, struct timespec *res);
       int clock_gettime(clockid_t clk_id, struct timespec *tp);
       int clock_settime(clockid_t clk_id, const struct timespec *tp);
       
                                  Link with -lrt.编译时使用链接库lrt

CLOCK_REALTIME:系统实时时间，使用此选项时功能相当于time(),如果系统时间被用户修改过,则对应的时间相应改变
CLOCK_MONOTONIC:从系统启动这一刻起开始计时,不受系统时间被用户改变的影响
CLOCK_PROCESS_CPUTIME_ID:本进程运行的CPU时间
CLOCK_THREAD_CPUTIME_ID:本线程运行的CPU时间

       #include <sys/time.h>
       int gettimeofday(struct timeval *tv, struct timezone *tz);
       int settimeofday(const struct timeval *tv, const struct timezone *tz);

struct tm { /* a broken-down time */
    int  tm_sec;     // 秒 【0~60】 60存在的原因是闰秒的存在
    int  tm_min;     //分
    int  tm_hour;    //时
    int  tm_mday;    //日
    int  tm_mon;     //月
    int  tm_year;    //年   结构中记录的是从1900至今的年数
    int  tm_wday;    //星期几  【0~6】
    int  tm_yday;    // 一年中第几天
    int  tm_isdst;   // 夏时制标志
};

#include <time.h>
struct tm *gmtime(const time_t *calptr);
struct tm *localtime(const time_t *calptr);
                               Both return: pointer to broken-down time,NULLon error

#include <time.h>
time_t mktime(struct tm *tmptr);
                   Returns: calendar time if OK,?1 on error

#include<stdio.h>
#include <time.h>
#include<sys/time.h>
int main(void)
{
        time_t calptr;
        if (time(&calptr) == -1)
        {
                printf("Error: time() failed!\n");
                exit(0);
        }
        printf("Time(time_t) now is: %d\n",(long) calptr);
        /*
         *      转换成可读到时间
         */
        struct tm *gmptr;               //国际标准时间
        struct tm *localptr;            //本地时间
 
/*      转换成国际标准时间      */
        printf("\n\n ----------gm time--------------\n");
        if (NULL == (gmptr = gmtime(&calptr)))
        {
                printf("Error: can‘t convert time_t to struct tm by gmtime()!\n");
                exit(0);
        }
        printf("year:%d,\tMonth:%d,\tDay:%d,\tWeek:%d\n", gmptr->tm_year, gmptr->tm_mon, gmptr->tm_mday, gmptr->tm_wday);
        printf("Hour:%d,\tMin:%d,\t,sec:%d\n", gmptr->tm_hour, gmptr->tm_min, gmptr->tm_sec);
        /*      转换成本地标准时间      */
        printf("\n\n ----------local time--------------\n");
        if (NULL == (localptr = localtime(&calptr)))
        {
                printf("Error: can‘t convert time_t to struct tm by localtime()!\n");
                exit(0);
        }
        printf("year:%d,\tMonth:%d,\tDay:%d,\tWeek:%d\n", localptr->tm_year, localptr->tm_mon, localptr->tm_mday, localptr->tm_wday);
        printf("Hour:%d,\tMin:%d,\t,sec:%d\n", localptr->tm_hour, localptr->tm_min, localptr->tm_sec);
        return 0;
}

windeal@ubuntu:~/Windeal/apue$ ./exe 
Time(time_t) now is: 1409207607
 ----------gm time--------------
year:114,	Month:7,	Day:28,	Week:4
Hour:6,	Min:33,	,sec:27
 ----------local time--------------
year:114,	Month:7,	Day:28,	Week:4
Hour:14,	Min:33,	,sec:27

#include <time.h>
size_t strftime(char *restrict buf,size_t maxsize,
                 const char *restrict format,
                 const struct tm *restrict tmptr);
size_t strftime_l(char *restrict buf,size_t maxsize,
                  const char *restrict format,
                  const struct tm *restrict tmptr,locale_t locale);
                ——Both return: number of characters stored in array if room, 0 otherwise

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int
main(void)
{
        time_t t;
        struct tm *tmp;
        char buf1[16];
        char buf2[64];
        time(&t);
        tmp = localtime(&t);
        if (strftime(buf1, 16, "time and date: %r, %a %b %d, %Y", tmp) == 0)
                printf("buffer length 16 is too small\n");
        else
                printf("%s\n", buf1);
        
        if (strftime(buf2, 64, "time and date: %r, %a %b %d, %Y", tmp) == 0)
                printf("buffer length 64 is too small\n");
        else
                printf("%s\n", buf2);
        exit(0);
}
~          

windeal@ubuntu:~/Windeal/apue$ ./exe 
buffer length 16 is too small
time and date: 02:43:55 PM, Thu Aug 28, 2014

#include <time.h>
char *strptime(const char *restrictbuf,const char *restrictformat,struct tm *restricttmptr);
                Returns: pointer to one character past last character parsed,NULLotherwise