linux_time_functions.c

Linux 环境下 C 开发的初始练习代码

// file linux_time_functions.c
//



#include <stdlib.h>
#include <time.h>
#include <sys/time.h>
#include <sys/timeb.h>

//------------------------------------------------------------------------------------

int isleap(int year) {

// every fourth year is a leap year 
// except for century years 
// that are not divisible by 400

  return (!(year % 4) && ((year % 100) || !(year % 400)));
}

//------------------------------------------------------------------------------------

struct tm* localtime(const time_t* gmt) {

#define SPD (24*60*60)    // seconds per day

  const unsigned int spm[12] = {
  0,
  31,
  31+28,
  31+28+31,
  31+28+31+30,
  31+28+31+30+31,
  31+28+31+30+31+30,
  31+28+31+30+31+30+31,
  31+28+31+30+31+30+31+31,
  31+28+31+30+31+30+31+31+30,
  31+28+31+30+31+30+31+31+30+31,
  31+28+31+30+31+30+31+31+30+31+30};

  static struct tm r;
  time_t t;
  struct timezone tz;
  long timezone;
  int i;
  time_t tmp;
  
  gettimeofday(0, &tz);
  
  timezone = tz.tz_minuteswest * 60L;
  t = *gmt - timezone;

  tmp = t % SPD;
  r.tm_sec = tmp % 60;
  tmp /= 60;
  r.tm_min = tmp % 60;
  r.tm_hour = tmp / 60;

  tmp = t / SPD;
  r.tm_wday = (4 + tmp) % 7;
  for (i=1970; ; ++i) {
    time_t k = isleap(i) ? 366 : 365;
    if (tmp >= k) tmp -= k;
    else         break;
  }
  r.tm_year = i - 1900;
  r.tm_yday = tmp;

  r.tm_mday = 1;
  if (isleap(i) && (tmp > 58)) {
    if (tmp == 59) r.tm_mday = 2;      // Feb 29
    tmp -= 1;
  }

  for (i=11; i && (spm[i]>tmp); --i) ;
  r.tm_mon = i;
  r.tm_mday += tmp - spm[i];
  
  return &r;
}

//------------------------------------------------------------------------------------

int main(void) {

  struct timeb timebuffer;
  struct tm *newtime;
  struct timeval tv;
  
  ftime(&timebuffer);
  printf("timebuffer.time   = %08X timebuffer.millitm = %3d \n",
          timebuffer.time,       timebuffer.millitm);

  gettimeofday(&tv, 0);
  printf("        tv.tv_sec = %08X         tv.tv_msec = %3d \n",
                  tv.tv_sec,               tv.tv_usec/1000);

//  newtime = localtime(&timebuffer.time);
  newtime = localtime(&tv.tv_sec);

  printf("%d  ", newtime->tm_year);
  printf("%d  ", newtime->tm_mon);
  printf("%d  ", newtime->tm_mday);
  printf("%d  ", newtime->tm_hour);
  printf("%d  ", newtime->tm_min);
  printf("%d\n", newtime->tm_sec);
}

//------------------------------------------------------------------------------------