#include <stdio.h>#include <string.h>#include <stdlib.h>#include <ctype.h>#include <stdint.h>struct tm {    /*     * the number of seconds after the minute, normally in the range     * 0 to 59, but can be up to 60 to allow for leap seconds     */    int tm_sec;    /* the number of minutes after the hour, in the range 0 to 59*/    int tm_min;    /* the number of hours past midnight, in the range 0 to 23 */    int tm_hour;    /* the day of the month, in the range 1 to 31 */    int tm_mday;    /* the number of months since January, in the range 0 to 11 */    int tm_mon;    /* the number of years since 1900 */    long tm_year;    /* the number of days since Sunday, in the range 0 to 6 */    int tm_wday;    /* the number of days since January 1, in the range 0 to 365 */    int tm_yday;    int tm_isdst;};static unsigned long mktime(const unsigned int year0, const unsigned int mon0,        const unsigned int day, const unsigned int hour,        const unsigned int min, const unsigned int sec){    unsigned int mon = mon0, year = year0;    /* 1..12 -> 11,12,1..10 */    if (0 >= (int) (mon -= 2)) {        mon += 12;    /* Puts Feb last since it has leap day */        year -= 1;    }    return ((((unsigned long)          (year/4 - year/100 + year/400 + 367*mon/12 + day) +          year*365 - 719499        )*24 + hour /* now have hours */      )*60 + min /* now have minutes */    )*60 + sec; /* finally seconds */}static struct tm * localtime_r(time_t *srctime,struct tm *tm_time){    long int n32_Pass4year,n32_hpery;    const static char Days[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};    const static int ONE_YEAR_HOURS = 8760;    time_t time = *srctime;    time=time+28800;    tm_time->tm_isdst=0;    if(time < 0)    {    time = 0;    }    tm_time->tm_sec=(int)(time % 60);    time /= 60;    tm_time->tm_min=(int)(time % 60);    time /= 60;    tm_time->tm_wday=(time/24+4)%7;    n32_Pass4year=((unsigned int)time / (1461L * 24L));    tm_time->tm_year=(n32_Pass4year << 2)+70;    time %= 1461L * 24L;    tm_time->tm_yday=(time/24)%365;    for (;;)    {        n32_hpery = ONE_YEAR_HOURS;        if ((tm_time->tm_year & 3) == 0)        {            n32_hpery += 24;        }        if (time < n32_hpery)        {            break;        }        tm_time->tm_year++;        time -= n32_hpery;    }    tm_time->tm_hour=(int)(time % 24);    time /= 24;    time++;    if ((tm_time->tm_year & 3) == 0)    {        if (time > 60)        {            time--;        }        else        {            if (time == 60)            {                tm_time->tm_mon = 1;                tm_time->tm_mday = 29;                return tm_time;            }        }    }    for (tm_time->tm_mon = 0;Days[tm_time->tm_mon] < time;tm_time->tm_mon++)    {        time -= Days[tm_time->tm_mon];    }    tm_time->tm_mday = (int)(time);    return tm_time;}int main(void){    uint32_t now = 1451577600; /*2016/01/01 00:00:00*/    struct tm tm = {0};    char *wday[] = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};    localtime_r(&now, &tm);    printf("%d/%d/%d \n", 1900 + tm.tm_year, 1 + tm.tm_mon, tm.tm_mday);    printf("%s %d:%d:%d \n", wday[tm.tm_wday], tm.tm_hour, tm.tm_min, tm.tm_sec);    now = mktime(1900 + tm.tm_year, 1 + tm.tm_mon, tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec);    printf("rtc value : %d\n", now);    return 0;}