tm

struct tm {
    int tm_sec;        seconds after the minute (from 0)
    int tm_min;        minutes after the hour (from 0)
    int tm_hour;       hour of the day (from 0)
    int tm_mday;       day of the month (from 1)
    int tm_mon;        month of the year (from 0)
    int tm_year;       years since 1900 (from 0)
    int tm_wday;       days since Sunday (from 0)
    int tm_yday;       day of the year (from 0)
    int tm_isdst;      Daylight Saving Time flag
    };

struct tm contains members that describe various properties of the calendar time. The members shown above can occur in any order,
interspersed with additional members. The comment following each member briefly describes its meaning.

The member tm_isdst contains:

a positive value if Daylight Saving Time is in effect
zero if Daylight Saving Time is not in effect
a negative value if the status of Daylight Saving Time is not known (so the target environment should attempt to determine its status)