time_t和tm互换

time_t mktime(struct tm *tm);
struct tm *gmtime(const time_t *timep);
struct tm *gmtime_r(const time_t *timep, struct tm *result);
struct tm *localtime(const time_t *timep);
struct tm *localtime_r(const time_t *timep, struct tm *result);
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Other:
time_t timelocal(struct tm *tm);
time_t timegm(struct tm *tm);