转换毫秒到time_t

Question

I have the number of milliseconds starting from 2004 to a specific date. I want to convert this to time_t to display it with ctime()?

Perhaps there is another method to visualize the date by this milliseconds timestamp, does anyone have one?

Answer 1

Assuming that by “starting from 2004” you mean “starting from 2004 at 00:00 UTC”, then

time_t time = 1072915200 + millis / 1000;

Beware that ctime() will display the result in local time instead of UTC.

Answer 2

time_t only has an accuracy of one second. If this is ok for you, you can calculate the time_t value for 2004-01-01 using mktime() and add it to your time-value in seconds.

struct tm tp;
memset(&tp, 0, sizeof(tp));
tp.tm_mday = 1;
tp.tm_mon = 0;
tp.tm_year = 2004 - 1900;
time_t offset = mktime(&tp);

time_t realtime = offset + yourtime / 1000;

printf("%s", ctime(&realtime));