Setup system datetime by local time zone name which is encoded according to IEEE 1003.1 (POSIX) in C－藍色情懷

Setup system datetime by local time zone name which is encoded according to IEEE 1003.1 (POSIX) in C

prerequisite：int matchStrPosAt()、char *strmhead()、char *strcutail()、int getTZ(char **tz)、int SetTZ(char *timezone)

/*
 * ctzset.c
 *
 * Created by Jackie Xie on 2011-08-20.
 * Copyright 2011 Jackie Xie. All rights reserved.
 *
 */

#include <ctype.h>
#include <errno.h>
#include <getopt.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <time.h>
#include <sys/time.h>

typedef enum {Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday} Days;
typedef enum {First, Second, Third, Fourth, Fifth} Weeks;
typedef enum {January = 1, February, March, April, May, June, July, August, September, October, November, December} Months; 	

typedef struct {
	int hour;
	int minute;
	int second;
} Time;

typedef struct {
	Time time;
	Days day;
	Weeks week;
	Months month;
	int year;
	time_t ptime;
} datetime;

int years[13] = {-1, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

/* ======================(function header)========================
Function Name:char* itos (){}
Description:to convert integer to string
Arguments:unsigned n
Return:a string
written by jackiexie
Date: 2007/07/10
================================================================*/
char tmpbuf[17];
char* itos (int n)
{
  int i=0,j;
  //char* s;
  //char* u;
  char s[17];
  //s= (char*) malloc(17);
  //u= (char*) malloc(17);
  
  do{
    s[i++]=(char)( n%10+48 );
    n-=n%10;
  }
  while((n/=10)>0);
  for (j=0;j<i;j++)
  tmpbuf[i-1-j]=s[j];

  tmpbuf[j]='\0';
  return tmpbuf;
}


/* ======================(function header)========================
Function Name: char *GetStrBetweenStr(char *,
 char *,char *)
Description: retrieve a string from between left position
 and right position string.
Arguments:char *s,char *lstr,char *rstr
Return: string
written by jackie xie
Date: 2007/07/10
================================================================*/
char *GetStrBetweenStr(char *s,char *lstr,char *rstr)
{
   char *p=s,*lp=s,*rp;
   do
   {
      /*trim(lstr);
 trim(rstr);*/
      lp=strstr(lp,lstr);
      if(lp)
      {
         rp=lstr;
         do lp++; while(*rp++);
         lp--;
         rp=strstr(lp,rstr);
         if(rp)
         {
            if(lp!=rp)
            {
               do *p++=*lp++; while(lp<rp);
               lp--;
            }
            rp=rstr;
            do lp++; while(*rp++);
            lp--;
         }
      }
   } while(lp);
   *p=0;
   return s;
}

/* ======================(function header)========================
Function Name: int matchStrPosAt (const char *, const char *)
Description: find the sub-string from the source string.
Arguments: const char *, const char *
Return: Returns "the array element number"(or "position") where 
 "sub-string" matches before in "original string", or return 
 "-1" if substr is not present in "original string".
written by jackie xie
Date : 2007/07/10
================================================================*/
/* 
 * delimiters <= n：return position before n-th matched substr.
 * delimiters = 0：do nothing.
 * delimiters >= n：return position after n-th matched substr.
 */
int matchStrPosAt (char * substr, char * str, int delimiters)
{
	int i = -1, k, str_index, total = 0;
	int substr_len = strlen(substr), str_len = strlen(str);
	int matchpos = -1;
	int delimiter[str_len], ind_delim = 0;
	//int n = abs(delimiters);

	for(k=0; k<=str_len ; k++)
		delimiter[k] = -1;

	if (str == NULL || substr == NULL) return -1;

	/* substr has to be smaller than str */
	if (substr_len > str_len) return -1;

	/* look through str for substr, stopping at end of string or when the length
 * of substr exceeds the remaining number of characters to be searched */ 
	while (str[++i] != '\0' && (str_len - i + 1) > substr_len) 
	{
		for (str_index = 0; str_index < substr_len; ++str_index)
		{
			/* definitely not at location i */
			if (str[i + str_index] != substr[str_index])
				break;
			/* if last letter matches, then we know the whole thing matched */
			else if (str_index == substr_len - 1)
			{
				if(delimiters >= 1)
				{
					i += substr_len -1;
					delimiter[++ind_delim] = i;
					//printf("delimiter[%d] = %d\n", ind_delim, delimiter[ind_delim]);
				}
				else if(delimiters == 0)
					return i;
				else if(delimiters == -1)
					total++;
			}
		}
	}

	if(delimiters == 0)
		return -1;						/* substr not present in str */
	else if(delimiters == -1)
		return total;					/* the total numbers of substr */
	else if(delimiters < ind_delim)
		matchpos = delimiter[delimiters];
	else
		matchpos = delimiter[ind_delim];

	return matchpos;
}

/* ======================(function header)========================
Function Name: int strcutail (char *str, const char *n, int pos)
Description: To remove the sub-string which is starting at 
 n-th delimiter(or include it) to the end of input string.
Arguments: char *, const char *
Return: Returns the string which was cut the tailed sub-string off.
written by Jackie Xie
Date : 2011/07/15
================================================================*/
char *strcutail (char *str, const char *n, int pos)
{
	int i, _newStrLen = matchStrPosAt(n, str, abs(pos));
	char* _new;
	
	if(_newStrLen > 0){
		if (pos >= 0)
			++_newStrLen;			
		if ((_new = (char *)malloc(_newStrLen)) == NULL)
			return "NULL";

		(_new)[_newStrLen] = '\0';		

		/* copy sub-string from the head of the string to the specified delimiter */
		for (i = 0; i < _newStrLen; ++i)
			(_new)[i] = str[i];

		strcpy(str, _new);
		free (_new);
	}
	return str;
}

/* ======================(function header)========================
Function Name: int strmhead (char *str, const char *n, int pos)
Description: To cut the front of sub-string which is starting at the
 matched delimiter and ending of the input string.
Arguments: char *, const char *
Return: The string which was cut the front of input string till the 
 specified delimiter.
written by Jackie Xie
Date : 2011/08/12
================================================================*/
char *strmhead (char *str, const char *n, int pos)
{
	int i, _matchedStrLen = matchStrPosAt(n, str, abs(pos));
	int str_len = strlen(str);
	int _newStrLen = 0;
	
	char* _new;
	
	if(_matchedStrLen > 0){
		if (pos >= 0)
			_matchedStrLen -= strlen(n);
			
		_newStrLen = str_len - _matchedStrLen;

		if ((_new = (char *)malloc(_newStrLen)) == NULL)
			return "NULL";

		(_new)[_newStrLen+1] = '\0';		

		/* copy sub-string from specified delimiter */
		for (i = 0; i < _newStrLen; ++i)
			(_new)[i] = str[_matchedStrLen +1 + i];
		strcpy(str, _new);
		free (_new);
	}
	
	return str;
}

bool isLeapYear (int year)
{
	if(((year % 4==0) && (year%100 != 0)) || (year % 400 == 0))
	   return true;
	else
		return false;	
}

bool IsLeapYear(int year)	
{					
	if(year%4==0) //必須能被4整除 
	{	
		 if(year%100==0)	
		 {	
				if(year%400==0)
					return	true;//如果以00結尾,還要能被400整除 
				else
					return false;		
		 }
		 else
		 	return true;		
	}
	else
		return false;	
}	

/* ======================(function header)========================
Function Name : Days get_day_code (int year){}
Description : The codes are: day_code (0 = Sun, 1 = Mon, etc.).
Arguments : a year as a decimal number with century.
Return : an user defined type 'Days' value.
written by Jackie Xie
Date : 2011/08/28
================================================================*/
Days get_day_code (int year)
{
	int day_code;
	int x1, x2, x3;
	x1 = (year - 1.)/ 4.0;
	x2 = (year - 1.)/ 100.;
	x3 = (year - 1.)/ 400.;
	day_code = (year + x1 - x2 + x3) %7;
	return day_code;
}

/* ======================(function header)========================
Function Name : int dayOfMonth(datetime dt){}
Description : To convert the day(Sun...Sat) of week(1~5) of 
 month(1~12) into the day of the month as a decimal 
 number(01-31).
Arguments : a user defined type 'datetime' dt.
Return : an interger value which range is from 1 to 31.
written by Jackie Xie
Date : 2011/08/28
================================================================*/
int dayOfMonth(datetime dt)
{
	int days, month;
	Days day_code;

	if(isLeapYear(dt.year))
		years[February] = 29;
	
	//printf("February have %d days in %d\n", years[February], dt.year);
	
	day_code = get_day_code(dt.year);
	for ( month = 1; month < dt.month; month++ )
	{
		/* set day_code for next month to begin */
		day_code = ( day_code + years[month] ) % 7;	
	}
	
	days = (dt.day >= day_code)?(dt.day - day_code + 1)+7*(dt.week-1): (7 - day_code + 1) + dt.day + 7*(dt.week-1);
	
	while(days > years[dt.month])
		days -= 7;
	
	return days;
}

/* ======================(function header)========================
Function Name :t ime_t str2datetime(char *datetime){}
Description : To Convert the string of datetime format into an interger 
 which unit is a time 'second'.
Arguments : char * tz
Return : an integer of type 'time_t '
written by Jackie Xie
Date : 2011/08/29
================================================================*/
time_t str2datetime(char *datetime)
{
	int year, month, day, hour, min, sec;
	struct tm *when;
	time_t tme;
	char tmp_time[32];
	strcpy(tmp_time, datetime);

	sscanf(tmp_time, "%4d-%02d-%02dT%02d:%02d:%02dZ", &year, &month, &day, &hour, &min, &sec);

	time(&tme);
	when = localtime(&tme);
	when->tm_year = year - 1900;
	when->tm_mon = month-1;
	when->tm_mday = day;
	when->tm_hour = hour;
	when->tm_min = min;
	when->tm_sec = sec;

	return(mktime(when));
}

/* ======================(function header)========================
Function Name:int getTZ(char **tz){}
Description : To find the time difference[Coordinated Universal Time
 (UTC)] between GMT and Local time zone.
Arguments : char ** tz
Return : a string with format "[+|-]hh:mm"
written by jackiexie
Date : 2011/06/02
Example :
 int main(int argc, char** argv)
 {
 char *tz;

 getTZ(&tz);
 printf("UTC%s", tz);

 return 0;
 }
================================================================*/
int getTZ(char **tz)
{
	struct tm *tptr;
	char UTC[20];
	time_t secs,l_secs,gmt_secs;
	float utc;
	char *min, *sign;
	int tmp;
	
	time(&secs);
	tptr = localtime(&secs);
	l_secs = mktime(tptr);
	tptr = gmtime(&secs);
	gmt_secs = mktime(tptr);
	utc = l_secs - gmt_secs;
	
	utc = utc/3600.0;
	//utc = -9.9;//-2.5;-3.5;-4.5;-9.5;-12;-10;5.75;8.75;12.75;13.75;14

	if(utc < 0)
		sign = strdup("-");
	else if(utc > 0)
		sign = strdup("+");

	tmp = utc * 60;
	tmp = abs(tmp) % 60;
	
	if(tmp == 30)
		min = strdup("30");
	else if(tmp == 45)
		min = strdup("45");
	else if(tmp != 0)
		min = strdup(itos(tmp));
	else
		min = strdup("00");

	tmp = (int)abs(utc);
	if(tmp <= 14 && tmp >= 10)
		sprintf(UTC, "%s%d:%s", sign, tmp, min);
	else if(tmp < 10 && tmp > 0)
		sprintf(UTC, "%s0%d:%s", sign, tmp, min);
	else
		sprintf(UTC, "00:00");

	*tz = strdup(UTC);
	//printf("%s(%s)\n", UTC, *tz);
	if(*tz == NULL)
		return -1;
	
	free(min);
	free(sign);
	
	return 0;
}

/* ======================(function header)========================
Function Name:int setTZ(char **tz){}
Description : To Setup the system date、time by timezone information.
Arguments : char * tz
Return : a string with format "[+|-]hh:mm"
written by Jackie Xie
Date : 2011/08/18
================================================================*/
int setTZ(char *timezone)
{
	struct tm *tptr;
	struct timeval tv;
	struct timezone tz;
	time_t secs;
	int utc = 0;
	int hsecs, msecs;
	int rc;
	char *sHour = strdup(timezone);
	char *sMin = strdup(timezone);

	(void) time(&secs);
	tptr = localtime(&secs);
	printf("The timezone is 'UTC%s'\n", timezone);
	printf("The current date/time :\n");
	printf(" Date : %02d-%02d-%02d\n", 1900+tptr->tm_year, tptr->tm_mon+1, tptr->tm_mday);
	printf(" Time : %02d:%02d:%02d\n\n", tptr->tm_hour, tptr->tm_min, tptr->tm_sec);

	if(strstr(timezone,":")){
		hsecs = atoi(strcutail(sHour, ":", -100)) * 3600;
		msecs = atoi(strmhead(sMin, ":", -100)) * 60;
	}
	else{
		hsecs = atoi(sHour) * 3600;
		msecs = 0;
	}	
	
	utc = hsecs + msecs;
	 (void) time(&secs);
	
	if(utc==0)
		tptr = localtime(&secs);
	else{
		secs += utc;
		tptr = gmtime(&secs);
	}

	// Make new system time.
	if ((tv.tv_sec = mktime(tptr)) == (time_t)-1)
	{
		printf("Cannot convert system time\n");
	}

	tz.tz_minuteswest = -(secs / 60);	
	tv.tv_usec = 0;
	rc = settimeofday(&tv, &tz);
	if ( rc != 0)
	{
		printf("Cannot set system time\n");
		printf("settimeofday() failed, " "errno = %d\n",errno);
		return -1;
	}
	else
		printf("settimeofday() successful.\n");

	printf("Update timezone:'UTC%s'\n", timezone);
	printf("The new date/time is :\n");
	printf(" Date: %02d-%02d-%02d\n", 1900+tptr->tm_year, tptr->tm_mon+1, tptr->tm_mday);
	printf(" Time: %02d:%02d:%02d\n\n", tptr->tm_hour, tptr->tm_min, tptr->tm_sec);

	free(sMin);
	free(sHour);
	
	return 0;
}

/* ======================(function header)===========================
Function Name:int setTZName(char *tzname){}
Description : To Setup the system date、time by a specified local timezone name which 
 is encoded according to IEEE 1003.1 (POSIX).

 Specifying the Time Zone with TZ

 In POSIX systems, a user can specify the time zone by means of the TZ environment variable. For information about how to set environment variables, see section Environment Variables. The functions for accessing the time zone are declared in `time.h'.

 You should not normally need to set TZ. If the system is configured properly, the default time zone will be correct. You might set TZ if you are using a computer over a network from a different time zone, and would like times reported to you in the time zone local to you, rather than what is local to the computer.

 In POSIX.1 systems the value of the TZ variable can be in one of three formats. With the GNU C library, the most common format is the last one, which can specify a selection from a large database of time zone information for many regions of the world. The first two formats are used to describe the time zone information directly, which is both more cumbersome and less precise. But the POSIX.1 standard only specifies the details of the first two formats, so it is good to be familiar with them in case you come across a POSIX.1 system that doesn't support a time zone information database.

 The first format is used when there is no Daylight Saving Time (or summer time) in the local time zone:

 std offset
 The std string specifies the name of the time zone. It must be three or more characters long and must not contain a leading colon, embedded digits, commas, nor plus and minus signs. There is no space character separating the time zone name from the offset, so these restrictions are necessary to parse the specification correctly.

 The offset specifies the time value you must add to the local time to get a Coordinated Universal Time value. It has syntax like [+|-]hh[:mm[:ss]]. This is positive if the local time zone is west of the Prime Meridian and negative if it is east. The hour must be between 0 and 23, and the minute and seconds between 0 and 59.

 The minutes ( mm) and seconds ( ss) are optional. The hour ( hh) shall be required and may be a single digit. The offset following std shall be required. If no offset follows dst, the alternative time is assumed to be one hour ahead of standard time. One or more digits may be used; the value is always interpreted as a decimal number. The hour shall be between zero and 24, and the minutes (and seconds)-if present-between zero and 59. The result of using values outside of this range is unspecified. If preceded by a '-', the timezone shall be east of the Prime Meridian; otherwise, it shall be west (which may be indicated by an optional preceding '+' ).

 For example, here is how we would specify Eastern Standard Time, but without any Daylight Saving Time alternative:

 EST+5
 The second format is used when there is Daylight Saving Time:

 std offset dst [offset],start[/time],end[/time]
 The initial std and offset specify the standard time zone, as described above. The dst string and offset specify the name and offset for the corresponding Daylight Saving Time zone; if the offset is omitted, it defaults to one hour ahead of standard time.

 The remainder of the specification describes when Daylight Saving Time is in effect. The start field is when Daylight Saving Time goes into effect and the end field is when the change is made back to standard time. The following formats are recognized for these fields:

 Jn
 This specifies the Julian day, with n between 1 and 365. February 29 is never counted, even in leap years.
 n
 This specifies the Julian day, with n between 0 and 365. February 29 is counted in leap years.

 Mm.w.d
 This specifies day d of week w of month m. The day d must be between 0 (Sunday) and 6. The week w must be between 1 and 5; week 1 is the first week in which day d occurs, and week 5 specifies the last d day in the month. The month m should be between 1 and 12.
 The time fields specify when, in the local time currently in effect, the change to the other time occurs. If omitted, the default is 02:00:00.

 For example, here is how you would specify the Eastern time zone in the United States, including the appropriate Daylight Saving Time and its dates of applicability. The normal offset from UTC is 5 hours; since this is west of the prime meridian, the sign is positive. Summer time begins on the first Sunday in April at 2:00am, and ends on the last Sunday in October at 2:00am.

 EST+5EDT,M4.1.0/2,M10.5.0/2

Arguments : char * tz
Return : a string with format "std offset dst [offset],start[/time],end[/time]"
written by Jackie Xie
Date : 2011/08/28
===================================================================*/
int setTZName(char *tzname)
{
	char *offsets = strdup(tzname);
	char stz[10]={0};
	char dtz[10]={0};
	char stz_offset[10]={0};
	char dtz_offset[10]={0};
	char *start_dst = NULL;
	char *end_dst = NULL;
	int len, i = -1, chstr = 0, chnum = 0;
	int stdlen = 0, dstlen = 0, sofflen = 0, dofflen = 0;
	char *times, *day, *week, *month, *year, *tmp;
	datetime sdst, edst;
	time_t ptime = 0;
	char data[32];
	
	sdst.ptime = edst.ptime = 0;

	if(strstr(tzname, ","))
	{
		datetime currtime;
		time_t currTime;
		struct tm* pLocalTime=NULL;
	
		times = strdup("00:00:00");
		day = strdup("00");
		week = strdup("0");
		month = strdup("00");
		year = strdup("0000");

		currTime = time(NULL);
		pLocalTime = localtime(&currTime);
		strftime(times, 10 ,"%H:%M:%S", pLocalTime);
		strftime(day, 3 ,"%d", pLocalTime);
		strftime(week, 2 ,"%w", pLocalTime);
		strftime(month, 3 ,"%m", pLocalTime);
		strftime(year, 5, "%Y", pLocalTime);
		
		tmp = strdup(times); currtime.time.hour = atoi(strcutail(tmp, ":", -1));
		tmp = strdup(times); currtime.time.minute = atoi(GetStrBetweenStr(tmp, ":", ":"));
		tmp = strdup(times); currtime.time.second = atoi(strmhead(tmp, ":", -2));
		currtime.day = atoi(day);
		currtime.week = atoi(week);
		currtime.month = atoi(month);
		currtime.year = atoi(year);
		printf("current time is '%4d-%02d-%02dT%02d:%02d:%02dZ'\n", currtime.year, currtime.month, currtime.day, currtime.time.hour, currtime.time.minute, currtime.time.second);

		start_dst = strdup(tzname);
		end_dst = strdup(tzname);
		tmp = strdup(tzname);
		strcutail(offsets, ",", -1);
		//printf("offsets = %s\n", offsets);
		start_dst = strdup(GetStrBetweenStr(tmp, ",", ","));
		if(!strstr(start_dst, "/"))
			sprintf(start_dst, "%s/2", start_dst);
		
		times = strdup(start_dst);
		day = strdup(start_dst);
		week = strdup(start_dst);
		month = strdup(start_dst);
		
		//sdst.time = atoi(strmhead(times, "/", -1));
		tmp = strdup(strmhead(times, "/", -1));
		if(strstr(tmp, ":"))
		{
			times = strdup(tmp); sdst.time.hour = atoi(strcutail(times, ":", -1));
			times = strdup(tmp); printf("times : %s\n", times);
			if(strstr(strmhead(times, ":", -1), ":")) sdst.time.minute = atoi(strcutail(times, ":", -1));
			else sdst.time.minute = atoi(times);
			times = strdup(tmp);
			if(strstr(strmhead(times, ":", -1), ":")) sdst.time.second = atoi(strmhead(times, ":", -1));
			else sdst.time.second = 0;
		}
		else
		{
			sdst.time.hour = atoi(tmp);
			sdst.time.minute = 0;
			sdst.time.second = 0;
		}
			
		sdst.day = atoi(strcutail(strmhead(day, ".", -2), "/", -1));
		sdst.week = atoi(GetStrBetweenStr(week, ".", "."));
		sdst.month = atoi(GetStrBetweenStr(month, "M", "."));

		strmhead(end_dst, ",", -2);
		if(!strstr(end_dst, "/"))
			sprintf(end_dst, "%s/2", end_dst);
		
		times = strdup(end_dst);
		day = strdup(end_dst);
		week = strdup(end_dst);
		month = strdup(end_dst);
		
		//edst.time = atoi(strmhead(times, "/", -1));
		tmp = strdup(strmhead(times, "/", -1));
		if(strstr(tmp, ":"))
		{
			times = strdup(tmp); edst.time.hour = atoi(strcutail(times, ":", -1));
			times = strdup(tmp);
			if(strstr(strmhead(times, ":", -1), ":")) edst.time.minute = atoi(strcutail(times, ":", -1));
			else edst.time.minute = atoi(times);
			times = strdup(tmp);
			if(strstr(strmhead(times, ":", -1), ":")) edst.time.second = atoi(strmhead(times, ":", -1));
			else edst.time.second = 0;
		}
		else
		{
			edst.time.hour = atoi(tmp);
			edst.time.minute = 0;
			edst.time.second = 0;
		}

		edst.day = atoi(strcutail(strmhead(day, ".", -2), "/", -1));
		edst.week = atoi(GetStrBetweenStr(week, ".", "."));
		edst.month = atoi(GetStrBetweenStr(month, "M", "."));
		
		if(sdst.month > edst.month)
		{
			sdst.year = currtime.year;
			edst.year = currtime.year + 1;
		}
		else
			sdst.year = edst.year = currtime.year;

		printf("start daylight saving time is '%4d-%02d-%02dT%02d:%02d:%02dZ'\n", sdst.year, sdst.month, dayOfMonth(sdst), sdst.time.hour, sdst.time.minute, sdst.time.second);
		printf("end daylight saving time is '%4d-%02d-%02dT%02d:%02d:%02dZ'\n", edst.year, edst.month, dayOfMonth(edst), edst.time.hour, edst.time.minute, edst.time.second);
		
		sprintf(data, "%4d-%02d-%02dT%02d:%02d:%02dZ\n", currtime.year, currtime.month,  currtime.day, currtime.time.hour, currtime.time.minute, currtime.time.second);
		currtime.ptime = str2datetime(data);
		//printf("%d\n", (int)currtime.ptime);
		ptime = currtime.ptime;

		sprintf(data, "%4d-%02d-%02dT%02d:%02d:%02dZ\n", sdst.year, sdst.month,  sdst.day, sdst.time.hour, sdst.time.minute, sdst.time.second);
		sdst.ptime = str2datetime(data);
		//printf("%d\n", (int)sdst.ptime);

		sprintf(data, "%4d-%02d-%02dT%02d:%02d:%02dZ\n", edst.year, edst.month,  edst.day, edst.time.hour, edst.time.minute, edst.time.second);
		edst.ptime = str2datetime(data);
		//printf("%d\n", (int)edst.ptime);
		
		free(times); free(tmp);
	}

	len = strlen(offsets);
	
	chstr = 0; chnum = 0;
	while (offsets[++i] != '\0')
	{
		if(isalpha(offsets[i]))
		{
			if(!chstr)
			{
				stz[stdlen] = offsets[i];
				stdlen++ ;
			}
			else
			{
				chnum = 1;
				dtz[dstlen] = offsets[i];
				dstlen++ ;
			}
		}
		else if(isdigit(offsets[i]) || offsets[i] == '+' || offsets[i] == '-' || offsets[i] == ':')
		{
			/* If preceded by a '-', the timezone shall be east of the Prime Meridian; 
 * otherwise, it shall be west (which may be indicated by an optional preceding '+' ).
 * Note: The +,- definition specifies east and west and not addition or subtraction, 
 * so be careful. (UTC+1 translates to <Timezone name>-1) 
 */
			chstr = 1;
			if(!chnum)
			{
				stz_offset[sofflen] = offsets[i];
				sofflen++ ;
			}
			else
			{
				dtz_offset[dofflen] = offsets[i];
				dofflen++ ;
			}
		}
	}
	
	
	{	
		char *shour = strdup(stz_offset);
		char *sminute = strdup(stz_offset);
		int doffset = 0, stzhour = atoi(shour) * (-1);

                stzhour = (strstr(tzname, "GMT") || strstr(tzname, "UTC"))?atoi(shour):atoi(shour) * (-1);

		if(dstlen && !dofflen) doffset = stzhour + 1; else doffset = stzhour;

		
		if(strstr(stz_offset, ":"))
		{
			strcutail(shour, ":", -1);
			strmhead(sminute, ":", -1);
			if(doffset > 0)
				sprintf(dtz_offset, "+%d:%s", doffset, sminute);
			else
				sprintf(dtz_offset, "%d:%s", doffset, sminute);
			if(stzhour > 0)
				sprintf(stz_offset, "+%d:%s", stzhour, sminute);
			else
				sprintf(stz_offset, "%d:%s", stzhour, sminute);
		}
		else
		{
			if(doffset > 0)
				sprintf(dtz_offset, "+%d", doffset);
			else
				sprintf(dtz_offset, "%d", doffset);
			if(stzhour > 0)
				sprintf(stz_offset, "+%d", stzhour);
			else
				sprintf(stz_offset, "%d", stzhour);
		}
		free(shour); free(sminute);
	}

	printf("Standard time zone is '%s%s'.\n", stz, stz_offset);
	if(dstlen) printf("Daylight Saving Time zone is '%s%s'.\n\n", dtz, dtz_offset);
	
	if(ptime >= sdst.ptime && ptime <= edst.ptime)
		setTZ(dtz_offset);
	else
		setTZ(stz_offset);

	free(offsets); free(start_dst); free(end_dst);
	return 0;
}

int main(int argc, char *argv[])
{
	//struct timeval tv;
	char help_msg[1024] = "Usage: tznset [-s <timezone>] [-x <timezone name is encoded according to IEEE 1003.1 (POSIX)>] [-i] [-h]\n\n";
	char *tz, *tzname;
	int c;
	
	strcat(help_msg, "tznset command summary\n");
	strcat(help_msg, "\tznset is a function to setup/get timezone infomation.\n");
	strcat(help_msg, "\t-s：setup datetime for specified timezone.\n");
	strcat(help_msg, "\t\t<timezone>：input format：'<+ | ->xx:xx' (x=[0~9]).\n");
	strcat(help_msg, "\t-x：setup datetime for specified timezone name.\n");
	strcat(help_msg, "\t\t<timezone name>：input format：'std offset dst [offset],start[/time],end[/time]' .\n");
	strcat(help_msg, "\t-i：To get te local timezone information.\n");
	strcat(help_msg, "\t-h：To show this help message.\n");

	while ((c = getopt(argc, argv, "s:x:i0:h0:?0")) != -1)
		switch (c) {
			case 's':
				tz = optarg;
				setTZ(tz);
				break;
			case 'x':
				tzname = optarg;
				setTZName(tzname);
				break;
			case 'i':
				getTZ(&tz);
				printf("本地時區是：UTC%s\n", tz);
				break;
			case 'h':
			case '?':
				fprintf(stderr, "%s", help_msg);
				exit(0);
				break;
			default:
				break;
		}
	return 0;
}

To run this program：

For example, we could choice the 'Europe／Lisbon' to setup the system datetime.

The execution result was shown as below：

[ jackie ~/test/opensource/datetime/tz ]# ./tznset -x WET0WEST,M3.5.0/1,M10.5.0
current time is '2011-08-31T11:30:28Z'
start daylight saving time is '2011-03-27T01:00:00Z'
end daylight saving time is '2011-10-30T02:00:00Z'
Standard time zone is 'WET0'.
Daylight Saving Time zone is 'WEST+1'.

The timezone is 'UTC+1'
The current date/time :
        Date : 2011-08-31
        Time : 11:30:28

Cannot set system time
settimeofday() failed, errno = 1
[ jackie ~/test/opensource/datetime/tz ]# sudo ./tznset -x WET0WEST,M3.5.0/1,M10.5.0
Password:
current time is '2011-08-31T11:30:34Z'
start daylight saving time is '2011-03-27T01:00:00Z'
end daylight saving time is '2011-10-30T02:00:00Z'
Standard time zone is 'WET0'.
Daylight Saving Time zone is 'WEST+1'.

The timezone is 'UTC+1'
The current date/time :
        Date : 2011-08-31
        Time : 11:30:34

settimeofday() successful.
Update timezone:'UTC+1'
The new date/time is :
        Date: 2011-08-31
        Time: 04:30:34

[ jackie ~/test/opensource/datetime/tz ]#

To setup the system date / time by Pacific/Chatham time zone：

Execution result was shown as following beown:

[ jackie ~/test/opensource/datetime/tz ]# sudo ./tznset -x CHAST-12:45CHADT,M10.1.0/2:45,M3.3.0/3:45
current time is '2011-08-31T13:50:52Z'
times : 2:45
start daylight saving time is '2011-10-02T02:45:00Z'
end daylight saving time is '2012-03-18T03:45:00Z'
Standard time zone is 'CHAST+12:45'.
Daylight Saving Time zone is 'CHADT+13:45'.

current ptime = 1314769852
start dst ptime = 1317321900
eended dst ptime = 1330458300

The timezone is 'UTC+12:45'
The current date/time :
        Date : 2011-08-31
        Time : 13:50:52

settimeofday() successful.
Update timezone:'UTC+12:45'
The new date/time is :
        Date: 2011-08-31
        Time: 18:35:52

[ jackie ~/test/opensource/datetime/tz ]#

To setup datetime by 'America/Sao Paulo' timezone：

After running tnzset：

[ jackie ~/test/opensource/datetime/tz ]# sudo ./tznset -x BRT3BRST,M10.3.0/0,M2.3.0/0
Password:
current time is '2011-08-31T14:05:28Z'
start daylight saving time is '2011-10-16T00:00:00Z'
end daylight saving time is '2012-02-19T00:00:00Z'
Standard time zone is 'BRT-3'.
Daylight Saving Time zone is 'BRST-2'.

The timezone is 'UTC-3'
The current date/time :
        Date : 2011-08-31
        Time : 14:05:28

settimeofday() successful.
Update timezone:'UTC-3'
The new date/time is :
        Date: 2011-08-31
        Time: 03:05:28

[ jackie ~/test/opensource/datetime/tz ]#

To setup datetime by 'Pacific／Marquesas' timezone：

[ jackie MacBook-Pro ~/tznconfig ]$ sudo ./tznconfig -x `xnvram get Pacific/Marquesas`
Password:
Standard time zone is 'MART9:30'.
The timezone is 'UTC-9:30:00'
The current date/time :
        Date : 2012-04-20
        Time : 16:49:50

hrsec = -32400
minsec = -1800
settimeofday() successful.
Update timezone:'UTC-9:30:00'
The new date/time is :
        Date: 2012-04-19
        Time: 23:19:50

[ jackie MacBook-Pro ~/tznconfig ]$

Time zone abbreviations

Abbreviation	Full name	Location	Time zone
A	Alpha Time Zone	Military	UTC + 1 hour
ADT	Atlantic Daylight Time	Atlantic	UTC - 3 hours
ADT	Atlantic Daylight Time	North America	UTC - 3 hours
AFT	Afghanistan Time	Asia	UTC + 4:30 hours
AKDT	Alaska Daylight Time	North America	UTC - 8 hours
AKST	Alaska Standard Time	North America	UTC - 9 hours
ALMT	Alma-Ata Time	Asia	UTC + 6 hours
AMST	Armenia Summer Time	Asia	UTC + 5 hours
AMST	Amazon Summer Time	South America	UTC - 3 hours
AMT	Armenia Time	Asia	UTC + 4 hours
AMT	Amazon Time	South America	UTC - 4 hours
ANAST	Anadyr Summer Time	Asia	UTC + 12 hours
ANAT	Anadyr Time	Asia	UTC + 12 hours
AQTT	Aqtobe Time	Asia	UTC + 5 hours
ART	Argentina Time	South America	UTC - 3 hours
AST	Arabia Standard Time	Asia	UTC + 3 hours
AST	Atlantic Standard Time	Atlantic	UTC - 4 hours
AST	Atlantic Standard Time	Caribbean	UTC - 4 hours
AST	Atlantic Standard Time	North America	UTC - 4 hours
AZOST	Azores Summer Time	Atlantic	UTC
AZOT	Azores Time	Atlantic	UTC - 1 hour
AZST	Azerbaijan Summer Time	Asia	UTC + 5 hours
AZT	Azerbaijan Time	Asia	UTC + 4 hours
B	Bravo Time Zone	Military	UTC + 2 hours
BNT	Brunei Darussalam Time	Asia	UTC + 8 hours
BOT	Bolivia Time	South America	UTC - 4 hours
BRST	Brasilia Summer Time	South America	UTC - 2 hours
BRT	Brasília time	South America	UTC - 3 hours
BST	Bangladesh Standard Time	Asia	UTC + 6 hours
BST	British Summer Time	Europe	UTC + 1 hour
BTT	Bhutan Time	Asia	UTC + 6 hours
C	Charlie Time Zone	Military	UTC + 3 hours
CAST	Casey Time	Antarctica	UTC + 8 hours
CAT	Central Africa Time	Africa	UTC + 2 hours
CCT	Cocos Islands Time	Indian Ocean	UTC + 6:30 hours
CDT	Central Daylight Time	Australia	UTC + 10:30 hours
CDT	Cuba Daylight Time	Caribbean	UTC - 4 hours
CDT	Central Daylight Time	North America	UTC - 5 hours
CEST	Central European Summer Time	Europe	UTC + 2 hours
CET	Central European Time	Africa	UTC + 1 hour
CET	Central European Time	Europe	UTC + 1 hour
CHADT	Chatham Island Daylight Time	Pacific	UTC + 13:45 hours
CHAST	Chatham Island Standard Time	Pacific	UTC + 12:45 hours
CKT	Cook Island Time	Pacific	UTC - 10 hours
CLST	Chile Summer Time	South America	UTC - 3 hours
CLT	Chile Standard Time	South America	UTC - 4 hours
COT	Colombia Time	South America	UTC - 5 hours
CST	China Standard Time	Asia	UTC + 8 hours
CST	Central Standard Time	Australia	UTC + 9:30 hours
CST	Central Standard Time	Central America	UTC - 6 hours
CST	Cuba Standard Time	Caribbean	UTC - 5 hours
CST	Central Standard Time	North America	UTC - 6 hours
CVT	Cape Verde Time	Africa	UTC - 1 hour
CXT	Christmas Island Time	Australia	UTC + 7 hours
ChST	Chamorro Standard Time	Pacific	UTC + 10 hours
D	Delta Time Zone	Military	UTC + 4 hours
DAVT	Davis Time	Antarctica	UTC + 7 hours
E	Echo Time Zone	Military	UTC + 5 hours
EASST	Easter Island Summer Time	Pacific	UTC - 5 hours
EAST	Easter Island Standard Time	Pacific	UTC - 6 hours
EAT	Eastern Africa Time	Africa	UTC + 3 hours
EAT	East Africa Time	Indian Ocean	UTC + 3 hours
ECT	Ecuador Time	South America	UTC - 5 hours
EDT	Eastern Daylight Time	Australia	UTC + 11 hours
EDT	Eastern Daylight Time	Caribbean	UTC - 4 hours
EDT	Eastern Daylight Time	North America	UTC - 4 hours
EDT	Eastern Daylight Time	Pacific	UTC + 11 hours
EEST	Eastern European Summer Time	Africa	UTC + 3 hours
EEST	Eastern European Summer Time	Asia	UTC + 3 hours
EEST	Eastern European Summer Time	Europe	UTC + 3 hours
EET	Eastern European Time	Africa	UTC + 2 hours
EET	Eastern European Time	Asia	UTC + 2 hours
EET	Eastern European Time	Europe	UTC + 2 hours
EGST	Eastern Greenland Summer Time	North America	UTC
EGT	East Greenland Time	North America	UTC - 1 hour
EST	Eastern Standard Time	Australia	UTC + 10 hours
EST	Eastern Standard Time	Central America	UTC - 5 hours
EST	Eastern Standard Time	Caribbean	UTC - 5 hours
EST	Eastern Standard Time	North America	UTC - 5 hours
ET	Tiempo del Este	Central America	UTC - 5 hours
ET	Tiempo del Este	Caribbean	UTC - 5 hours
ET	Tiempo Del Este	North America	UTC - 5 hours
F	Foxtrot Time Zone	Military	UTC + 6 hours
FJST	Fiji Summer Time	Pacific	UTC + 13 hours
FJT	Fiji Time	Pacific	UTC + 12 hours
FKST	Falkland Islands Summer Time	South America	UTC - 3 hours
FKT	Falkland Island Time	South America	UTC - 4 hours
FNT	Fernando de Noronha Time	South America	UTC - 2 hours
G	Golf Time Zone	Military	UTC + 7 hours
GALT	Galapagos Time	Pacific	UTC - 6 hours
GAMT	Gambier Time	Pacific	UTC - 9 hours
GET	Georgia Standard Time	Asia	UTC + 4 hours
GFT	French Guiana Time	South America	UTC - 3 hours
GILT	Gilbert Island Time	Pacific	UTC + 12 hours
GMT	Greenwich Mean Time	Africa	UTC
GMT	Greenwich Mean Time	Europe	UTC
GST	Gulf Standard Time	Asia	UTC + 4 hours
GYT	Guyana Time	South America	UTC - 4 hours
H	Hotel Time Zone	Military	UTC + 8 hours
HAA	Heure Avancée de l'Atlantique	Atlantic	UTC - 3 hours
HAA	Heure Avancée de l'Atlantique	North America	UTC - 3 hours
HAC	Heure Avancée du Centre	North America	UTC - 5 hours
HADT	Hawaii-Aleutian Daylight Time	North America	UTC - 9 hours
HAE	Heure Avancée de l'Est	Caribbean	UTC - 4 hours
HAE	Heure Avancée de l'Est	North America	UTC - 4 hours
HAP	Heure Avancée du Pacifique	North America	UTC - 7 hours
HAR	Heure Avancée des Rocheuses	North America	UTC - 6 hours
HAST	Hawaii-Aleutian Standard Time	North America	UTC - 10 hours
HAT	Heure Avancée de Terre-Neuve	North America	UTC - 2:30 hours
HAY	Heure Avancée du Yukon	North America	UTC - 8 hours
HKT	Hong Kong Time	Asia	UTC + 8 hours
HLV	Hora Legal de Venezuela	South America	UTC - 4:30 hours
HNA	Heure Normale de l'Atlantique	Atlantic	UTC - 4 hours
HNA	Heure Normale de l'Atlantique	Caribbean	UTC - 4 hours
HNA	Heure Normale de l'Atlantique	North America	UTC - 4 hours
HNC	Heure Normale du Centre	Central America	UTC - 6 hours
HNC	Heure Normale du Centre	North America	UTC - 6 hours
HNE	Heure Normale de l'Est	Central America	UTC - 5 hours
HNE	Heure Normale de l'Est	Caribbean	UTC - 5 hours
HNE	Heure Normale de l'Est	North America	UTC - 5 hours
HNP	Heure Normale du Pacifique	North America	UTC - 8 hours
HNR	Heure Normale des Rocheuses	North America	UTC - 7 hours
HNT	Heure Normale de Terre-Neuve	North America	UTC - 3:30 hours
HNY	Heure Normale du Yukon	North America	UTC - 9 hours
HOVT	Hovd Time	Asia	UTC + 7 hours
I	India Time Zone	Military	UTC + 9 hours
ICT	Indochina Time	Asia	UTC + 7 hours
IDT	Israel Daylight Time	Asia	UTC + 3 hours
IOT	Indian Chagos Time	Indian Ocean	UTC + 6 hours
IRDT	Iran Daylight Time	Asia	UTC + 4:30 hours
IRKST	Irkutsk Summer Time	Asia	UTC + 9 hours
IRKT	Irkutsk Time	Asia	UTC + 8 hours
IRST	Iran Standard Time	Asia	UTC + 3:30 hours
IST	Israel Standard Time	Asia	UTC + 2 hours
IST	India Standard Time	Asia	UTC + 5:30 hours
IST	Irish Standard Time	Europe	UTC + 1 hour
JST	Japan Standard Time	Asia	UTC + 9 hours
K	Kilo Time Zone	Military	UTC + 10 hours
KGT	Kyrgyzstan Time	Asia	UTC + 6 hours
KRAST	Krasnoyarsk Summer Time	Asia	UTC + 8 hours
KRAT	Krasnoyarsk Time	Asia	UTC + 7 hours
KST	Korea Standard Time	Asia	UTC + 9 hours
KUYT	Kuybyshev Time	Europe	UTC + 4 hours
L	Lima Time Zone	Military	UTC + 11 hours
LHDT	Lord Howe Daylight Time	Australia	UTC + 11 hours
LHST	Lord Howe Standard Time	Australia	UTC + 10:30 hours
LINT	Line Islands Time	Pacific	UTC + 14 hours
M	Mike Time Zone	Military	UTC + 12 hours
MAGST	Magadan Summer Time	Asia	UTC + 12 hours
MAGT	Magadan Time	Asia	UTC + 11 hours
MART	Marquesas Time	Pacific	UTC - 9:30 hours
MAWT	Mawson Time	Antarctica	UTC + 5 hours
MDT	Mountain Daylight Time	North America	UTC - 6 hours
MHT	Marshall Islands Time	Pacific	UTC + 12 hours
MMT	Myanmar Time	Asia	UTC + 6:30 hours
MSD	Moscow Daylight Time	Europe	UTC + 4 hours
MSK	Moscow Standard Time	Europe	UTC + 3 hours
MST	Mountain Standard Time	North America	UTC - 7 hours
MUT	Mauritius Time	Africa	UTC + 4 hours
MVT	Maldives Time	Asia	UTC + 5 hours
MYT	Malaysia Time	Asia	UTC + 8 hours
N	November Time Zone	Military	UTC - 1 hour
NCT	New Caledonia Time	Pacific	UTC + 11 hours
NDT	Newfoundland Daylight Time	North America	UTC - 2:30 hours
NFT	Norfolk Time	Australia	UTC + 11:30 hours
NOVST	Novosibirsk Summer Time	Asia	UTC + 7 hours
NOVT	Novosibirsk Time	Asia	UTC + 6 hours
NPT	Nepal Time	Asia	UTC + 5:45 hours
NST	Newfoundland Standard Time	North America	UTC - 3:30 hours
NUT	Niue Time	Pacific	UTC - 11 hours
NZDT	New Zealand Daylight Time	Antarctica	UTC + 13 hours
NZDT	New Zealand Daylight Time	Pacific	UTC + 13 hours
NZST	New Zealand Standard Time	Antarctica	UTC + 12 hours
NZST	New Zealand Standard Time	Pacific	UTC + 12 hours
O	Oscar Time Zone	Military	UTC - 2 hours
OMSST	Omsk Summer Time	Asia	UTC + 7 hours
OMST	Omsk Standard Time	Asia	UTC + 6 hours
P	Papa Time Zone	Military	UTC - 3 hours
PDT	Pacific Daylight Time	North America	UTC - 7 hours
PET	Peru Time	South America	UTC - 5 hours
PETST	Kamchatka Summer Time	Asia	UTC + 12 hours
PETT	Kamchatka Time	Asia	UTC + 12 hours
PGT	Papua New Guinea Time	Pacific	UTC + 10 hours
PHOT	Phoenix Island Time	Pacific	UTC + 13 hours
PHT	Philippine Time	Asia	UTC + 8 hours
PKT	Pakistan Standard Time	Asia	UTC + 5 hours
PMDT	Pierre & Miquelon Daylight Time	North America	UTC - 2 hours
PMST	Pierre & Miquelon Standard Time	North America	UTC - 3 hours
PONT	Pohnpei Standard Time	Pacific	UTC + 11 hours
PST	Pacific Standard Time	North America	UTC - 8 hours
PST	Pitcairn Standard Time	Pacific	UTC - 8 hours
PT	Tiempo del Pacífico	North America	UTC - 8 hours
PWT	Palau Time	Pacific	UTC + 9 hours
PYST	Paraguay Summer Time	South America	UTC - 3 hours
PYT	Paraguay Time	South America	UTC - 4 hours
Q	Quebec Time Zone	Military	UTC - 4 hours
R	Romeo Time Zone	Military	UTC - 5 hours
RET	Reunion Time	Africa	UTC + 4 hours
S	Sierra Time Zone	Military	UTC - 6 hours
SAMT	Samara Time	Europe	UTC + 4 hours
SAST	South Africa Standard Time	Africa	UTC + 2 hours
SBT	Solomon IslandsTime	Pacific	UTC + 11 hours
SCT	Seychelles Time	Africa	UTC + 4 hours
SGT	Singapore Time	Asia	UTC + 8 hours
SRT	Suriname Time	South America	UTC - 3 hours
SST	Samoa Standard Time	Pacific	UTC - 11 hours
T	Tango Time Zone	Military	UTC - 7 hours
TAHT	Tahiti Time	Pacific	UTC - 10 hours
TFT	French Southern and Antarctic Time	Indian Ocean	UTC + 5 hours
TJT	Tajikistan Time	Asia	UTC + 5 hours
TKT	Tokelau Time	Pacific	UTC - 10 hours
TLT	East Timor Time	Asia	UTC + 9 hours
TMT	Turkmenistan Time	Asia	UTC + 5 hours
TVT	Tuvalu Time	Pacific	UTC + 12 hours
U	Uniform Time Zone	Military	UTC - 8 hours
ULAT	Ulaanbaatar Time	Asia	UTC + 8 hours
UYST	Uruguay Summer Time	South America	UTC - 2 hours
UYT	Uruguay Time	South America	UTC - 3 hours
UZT	Uzbekistan Time	Asia	UTC + 5 hours
V	Victor Time Zone	Military	UTC - 9 hours
VET	Venezuelan Standard Time	South America	UTC - 4:30 hours
VLAST	Vladivostok Summer Time	Asia	UTC + 11 hours
VLAT	Vladivostok Time	Asia	UTC + 10 hours
VUT	Vanuatu Time	Pacific	UTC + 11 hours
W	Whiskey Time Zone	Military	UTC - 10 hours
WAST	West Africa Summer Time	Africa	UTC + 2 hours
WAT	West Africa Time	Africa	UTC + 1 hour
WDT	Western Daylight Time	Australia	UTC + 9 hours
WEST	Western European Summer Time	Africa	UTC + 1 hour
WEST	Western European Summer Time	Europe	UTC + 1 hour
WET	Western European Time	Africa	UTC
WET	Western European Time	Europe	UTC
WFT	Wallis and Futuna Time	Pacific	UTC + 12 hours
WGST	Western Greenland Summer Time	North America	UTC - 2 hours
WGT	West Greenland Time	North America	UTC - 3 hours
WIB	Western Indonesian Time	Asia	UTC + 7 hours
WIT	Eastern Indonesian Time	Asia	UTC + 9 hours
WITA	Central Indonesian Time	Asia	UTC + 8 hours
WST	Western Sahara Summer Time	Africa	UTC + 1 hour
WST	Western Standard Time	Australia	UTC + 8 hours
WST	West Samoa Time	Pacific	UTC - 11 hours
WT	Western Sahara Standard Time	Africa	UTC
X	X-ray Time Zone	Military	UTC - 11 hours
Y	Yankee Time Zone	Military	UTC - 12 hours
YAKST	Yakutsk Summer Time	Asia	UTC + 10 hours
YAKT	Yakutsk Time	Asia	UTC + 9 hours
YAPT	Yap Time	Pacific	UTC + 10 hours
YEKST	Yekaterinburg Summer Time	Asia	UTC + 6 hours
YEKT	Yekaterinburg Time	Asia	UTC + 5 hours
Z	Zulu Time Zone	Military	UTC