How to convert a time into epoch time?

Question

Say I have a specific instant in time where I know the hour, minute, day, second, month, year, etc; how can I convert this epoch time (seconds since 1970)?

I can\'t

Answer 1

mktime and memset is most portable for me:

struct tm t;
memset(&t, 0, sizeof(tm)); // Initalize to all 0's
t.tm_year = 112; // This is year-1900, so 112 = 2012
t.tm_mon = 8;
t.tm_mday = 15;
t.tm_hour = 21;
t.tm_min = 54;
t.tm_sec = 13;
time_t time_since_epoch = mktime(&t);