时间结构体tm中 成员 tm_yday和成员tm_isdst 是什么意思？

[teal]

struct tm{
tm_sec
tm_min
tm_hour
tm_mday
tm_mon
tm_year
tm_wday
tm_yday
tm_isdst
}

最后两个变量是什么意思？

[fireseed]

#ifndef _TM_DEFINED
struct tm {
int tm_sec; /* seconds after the minute - [0,59] */
int tm_min; /* minutes after the hour - [0,59] */
int tm_hour; /* hours since midnight - [0,23] */
int tm_mday; /* day of the month - [1,31] */
int tm_mon; /* months since January - [0,11] */
int tm_year; /* years since 1900 */
int tm_wday; /* days since Sunday - [0,6] */
int tm_yday; /* days since January 1 - [0,365] */
int tm_isdst; /* daylight savings time flag */
};
#define _TM_DEFINED
#endif