Linux学习笔记（05-25）时间接口

(1)
time_t time( time_t * t );
此函数会返回从公元1970年1月1日的UTC时间从0时0分0秒算起到现在所经过的秒数。如果t 并非空指针的话，此函数也会将返回值存到t指针所指的内存。

(2)
struct tm *localtime( const time_t *timer );
struct tm* localtime_r( const time_t* timer, struct tm* result );
将time_t*所指的秒数转换得到当前时间的tm结构

(3)
time_t mktime( struct tm* timeptr );
用来将参数timeptr所指的tm结构数据转换成从公元1970年1月1日0时0分0 秒算起至今的UTC时间所经过的秒数。与localtime_r互为相反过程。

(4)
char* ctime( const time_t* timer );
char* ctime_r( const time_t* timer,  char* buf );
    将time_t*所指的秒数格式化输出。

(5) 

size_t strftime(char *s, size_t max, const char *format, const struct tm *tm);
    将参数tm的时间结构依照参数format所指定的字符串格式做转换，转换后的字符串将复制到参数s所指的字符串数组中，该字符串的最大长度为参数max所控制。可实现与ctime相反的操作。

 

(6)

int clock_gettime( clockid_t clock_id, struct timespec * tp );
int gettimeofday( struct timeval * when,  void * not_used ); 
    获取当前时间。前者使用的数据结构中有一个纳秒级的参数，而后者是微秒，所以可以认为前者的精度比较高。

(7)

int clock_settime( clockid_t id, const struct timespec * tp );

int settimeofday( const struct timeval *when,  void *not_used );
设置当前时间

对应结构体定义：
struct tm
{
 int  tm_sec;   //seconds after the minute -- [0,61]
 int  tm_min;   //minutes after the hour   -- [0,59]
 int  tm_hour;  //hours after midnight     -- [0,23]
 int  tm_mday;  //day of the month         -- [1,31]
 int  tm_mon;   //months since January     -- [0,11]
 int  tm_year;  //years since 1900
 int  tm_wday;  //days since Sunday        -- [0,6]
 int  tm_yday;  //days since January 1     -- [0,365]
 int  tm_isdst; //Daylight Savings Time flag
 long int tm_gmtoff; //Offset from gmt
 const char *tm_zone; //String for zone name
};
 
struct timespec
{
 time_t   tv_sec;//The number of seconds since 1970
 long     tv_nsec;//The number of nanoseconds
}
 
struct   timeval
{  
 int tv_sec;   //seconds        
 int tv_usec;  //microseconds               
};
 
struct itimerspec
{  
 struct     timespec   it_interval;  //timer   period   
 struct     timespec   it_value;     //timer   expiration     
};
 
struct itimerval
{  
 struct timeval   it_interval;  //timer   interval          
 struct timeval   it_value;     //current   value          
}; 

举例：

(1)

typedef struct
{
    unsigned short Year;    //year;
    unsigned char Month;   //month;
unsigned char Day;     //day;
    unsigned char Hour;    //hour;
    unsigned char Minute;  //minute;
    unsigned char Sec;     //second;
    unsigned char Week;
}TS;


//获取日期
void TSGet(TS *ts) {
    struct tm tmp_tm;
    time_t time_of_day;
    time_of_day = time(NULL);
    localtime_r(&time_of_day, &tmp_tm);
    ts->Year = tmp_tm.tm_year + 1900;
    ts->Month = tmp_tm.tm_mon + 1;
    ts->Day = tmp_tm.tm_mday;
    ts->Hour = tmp_tm.tm_hour;
    ts->Minute = tmp_tm.tm_min;
    ts->Sec = tmp_tm.tm_sec;
    ts->Week = tmp_tm.tm_wday;
}


//设置时间
void TSSet(TS ts) {
    struct tm tmpsec;
    struct timespec rtime;
    struct timespec cur_time;
    tmpsec.tm_sec = ts.Sec;
    tmpsec.tm_min = ts.Minute;
    tmpsec.tm_hour = ts.Hour;
    tmpsec.tm_mday = ts.Day;
    tmpsec.tm_mon = ts.Month - 1;
    tmpsec.tm_year = ts.Year - 1900;
    rtime.tv_sec = mktime(&tmpsec);
    clock_gettime(CLOCK_REALTIME, &cur_time);
    rtime.tv_nsec = cur_time.tv_nsec;
    clock_settime(CLOCK_REALTIME, &rtime);
}


 
(2)：
int main(int argc, char *argv[])
{
    struct tm tmp_tm;
    time_t time_of_day;//1970/1/1 0:0:0至今的秒数
    struct timespec spec;
    char buf[30];
    time_of_day = time(NULL);
    printf("time_of_day = %ld\n", time_of_day);
    localtime_r(&time_of_day, &tmp_tm);
    printf("%d-%d-%d, %d:%d:%d\n", tmp_tm.tm_year,tmp_tm.tm_mon,tmp_tm.tm_mday,
                                    tmp_tm.tm_hour,tmp_tm.tm_min,tmp_tm.tm_sec);
    spec.tv_sec = mktime(&tmp_tm);
    printf("spec = %ld\n", spec.tv_sec);


    ctime_r(&spec.tv_sec, buf);
    printf("%s\n",buf);
}
结果：
time_of_day = 1276169161
110-5-10, 11:26:1
spec = 1276169161
Thu Jun 10 11:26:01 2010
 
(3)：
void function()
{
 unsigned int i;
 sleep(3);
 for(i=0;i<100;i++ )
  printf("i = %d\n",i);
}
 
int main(int argc, char *argv[])
{
 struct timeval tpstart,tpend;
 float timeuse=0;
 gettimeofday(&tpstart,NULL);
 function();
 gettimeofday(&tpend,NULL);
 timeuse=1000000*(tpend.tv_sec-tpstart.tv_sec);
 timeuse=timeuse+tpend.tv_usec-tpstart.tv_usec;
 timeuse/=1000000;
 printf("Used Time:%f\n",timeuse);
}