C语言如何实现Unix时间戳与本地时间转化

#include <stdio.h>
#include <stdbool.h>

#define UTC_BASE_YEAR 1970
#define MONTH_PER_YEAR 12
#define DAY_PER_YEAR 365
#define SEC_PER_DAY 86400
#define SEC_PER_HOUR 3600
#define SEC_PER_MIN 60

/* 每个月的天数 */
const unsigned char g_day_per_mon[MONTH_PER_YEAR] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

/* 自定义的时间结构体 */
typedef struct
{
 unsigned short nYear;
 unsigned char nMonth;
 unsigned char nDay;
 unsigned char nHour;
 unsigned char nMin;
 unsigned char nSec;
 unsigned char DayIndex; /* 0 = Sunday */
} mytime_struct;

/*
 * 功能：
 * 判断是否是闰年
 * 参数：
 * year：需要判断的年份数
 *
 * 返回值：
 * 闰年返回1，否则返回0
 */
unsigned char applib_dt_is_leap_year(unsigned short year)
{
 /*----------------------------------------------------------------*/
 /* Local Variables      */
 /*----------------------------------------------------------------*/

 /*----------------------------------------------------------------*/
 /* Code Body       */
 /*----------------------------------------------------------------*/
 if ((year % 400) == 0) {
 return 1;
 } else if ((year % 100) == 0) {
 return 0;
 } else if ((year % 4) == 0) {
 return 1;
 } else {
 return 0;
 }
}

/*
 * 功能：
 * 得到每个月有多少天
 * 参数：
 * month：需要得到天数的月份数
 * year：该月所对应的年份数
 *
 * 返回值：
 * 该月有多少天
 *
 */
unsigned char applib_dt_last_day_of_mon(unsigned char month, unsigned short year)
{
 /*----------------------------------------------------------------*/
 /* Local Variables      */
 /*----------------------------------------------------------------*/

 /*----------------------------------------------------------------*/
 /* Code Body       */
 /*----------------------------------------------------------------*/
 if ((month == 0) || (month > 12)) {
 return g_day_per_mon[1] + applib_dt_is_leap_year(year);
 }

 if (month != 2) {
 return g_day_per_mon[month - 1];
 } else {
 return g_day_per_mon[1] + applib_dt_is_leap_year(year);
 }
}

/*
 * 功能：
 * 根据给定的日期得到对应的星期
 * 参数：
 * year：给定的年份
 * month：给定的月份
 * day：给定的天数
 *
 * 返回值：
 * 对应的星期数，0 - 星期天 ... 6 - 星期六
 */
unsigned char applib_dt_dayindex(unsigned short year, unsigned char month, unsigned char day)
{
 char century_code, year_code, month_code, day_code;
 int week = 0;

 century_code = year_code = month_code = day_code = 0;

 if (month == 1 || month == 2) {
 century_code = (year - 1) / 100;
 year_code = (year - 1) % 100;
 month_code = month + 12;
 day_code = day;
 } else {
 century_code = year / 100;
 year_code = year % 100;
 month_code = month;
 day_code = day;
 }

 /* 根据蔡勒公式计算星期 */
 week = year_code + year_code / 4 + century_code / 4 - 2 * century_code + 26 * ( month_code + 1 ) / 10 + day_code - 1;
 week = week > 0 ? (week % 7) : ((week % 7) + 7);

 return week;
}

/*
 * 功能：
 * 根据UTC时间戳得到对应的日期
 * 参数：
 * utc_sec：给定的UTC时间戳
 * result：计算出的结果
 * daylightSaving：是否是夏令时
 *
 * 返回值：
 * 无
 */
void utc_sec_2_mytime(unsigned int utc_sec, mytime_struct *result, bool daylightSaving)
{
 /*----------------------------------------------------------------*/
 /* Local Variables      */
 /*----------------------------------------------------------------*/
 int sec, day;
 unsigned short y;
 unsigned char m;
 unsigned short d;
 unsigned char dst;

 /*----------------------------------------------------------------*/
 /* Code Body       */
 /*----------------------------------------------------------------*/

 if (daylightSaving) {
 utc_sec += SEC_PER_HOUR;
 }

 /* hour, min, sec */
 /* hour */
 sec = utc_sec % SEC_PER_DAY;
 result->nHour = sec / SEC_PER_HOUR;

 /* min */
 sec %= SEC_PER_HOUR;
 result->nMin = sec / SEC_PER_MIN;

 /* sec */
 result->nSec = sec % SEC_PER_MIN;

 /* year, month, day */
 /* year */
 /* year */
 day = utc_sec / SEC_PER_DAY;
 for (y = UTC_BASE_YEAR; day > 0; y++) {
 d = (DAY_PER_YEAR + applib_dt_is_leap_year(y));
 if (day >= d)
 {
  day -= d;
 }
 else
 {
  break;
 }
 }

 result->nYear = y;

 for (m = 1; m < MONTH_PER_YEAR; m++) {
 d = applib_dt_last_day_of_mon(m, y);
 if (day >= d) {
  day -= d;
 } else {
  break;
 }
 }

 result->nMonth = m;
 result->nDay = (unsigned char) (day + 1);
 /* 根据给定的日期得到对应的星期 */
 result->DayIndex = applib_dt_dayindex(result->nYear, result->nMonth, result->nDay);
}

/*
 * 功能：
 * 根据时间计算出UTC时间戳
 * 参数：
 * currTime：给定的时间
 * daylightSaving：是否是夏令时
 *
 * 返回值：
 * UTC时间戳
 */
unsigned int mytime_2_utc_sec(mytime_struct *currTime, bool daylightSaving)
{
 /*----------------------------------------------------------------*/
 /* Local Variables      */
 /*----------------------------------------------------------------*/
 unsigned short i;
 unsigned int no_of_days = 0;
 int utc_time;
 unsigned char dst;

 /*----------------------------------------------------------------*/
 /* Code Body       */
 /*----------------------------------------------------------------*/
 if (currTime->nYear < UTC_BASE_YEAR) {
 return 0;
 }

 /* year */
 for (i = UTC_BASE_YEAR; i < currTime->nYear; i++) {
 no_of_days += (DAY_PER_YEAR + applib_dt_is_leap_year(i));
 }

 /* month */
 for (i = 1; i < currTime->nMonth; i++) {
 no_of_days += applib_dt_last_day_of_mon((unsigned char) i, currTime->nYear);
 }

 /* day */
 no_of_days += (currTime->nDay - 1);

 /* sec */
 utc_time = (unsigned int) no_of_days * SEC_PER_DAY + (unsigned int) (currTime->nHour * SEC_PER_HOUR +
        currTime->nMin * SEC_PER_MIN + currTime->nSec);

 if (dst && daylightSaving) {
 utc_time -= SEC_PER_HOUR;
 }

 return utc_time;
}

int main(int argc, char *argv[])
{
 mytime_struct my_time;
 unsigned int sec;
 char *DayIndex[] = {"Sun.", "Mon.", "Tues.", "Wed.", "Thur.", "Fri.", "Sat."};

 /* 这里根据UTC时间戳计算出来的时间是零时区的时间，所以如果要转化成北京时间就需要多加8小时 */
 utc_sec_2_mytime(1484537668 + 8 * SEC_PER_HOUR, &my_time, false);


 printf("%d-%d-%d %d:%d:%d %s\n", my_time.nYear, my_time.nMonth, my_time.nDay,
  my_time.nHour, my_time.nMin, my_time.nSec, DayIndex[my_time.DayIndex]);

 sec = mytime_2_utc_sec(&my_time, false);
 printf("sec = %d\n", sec);

 return 0;
}