From Erlang Community

Revision as of 12:51, 24 September 2006

Problem

You have a date and time in Erlang Epoch seconds (i.e., Gregorian calendar year 0 seconds), and you want to calculate the individual DMYHMS values from it.

Solution

In recipe TimeToday we did exactly this but only for the current date. How about if we wanted to get the date, and time (DMYHMS) associated to a particular number of seconds? Once more we would use gre.

1> Seconds = 1083022458.
1083022458
2> DateTime = calendar:gregorian_seconds_to_datetime(Seconds).
{{34,4,26},{23,34,18}}
3> {{Year, Month, Day}, {Hour, Min, Sec}} = DateTime.
{{34,4,26},{23,34,18}}
4> io:fwrite("Today's Date is ~2B/~2B/~4B ~2B:~2.10.0B:~2.10.0B\n",
4> [Month, Day, Year, Hour, Min, Sec]).
Today's Date is  4/26/  34 23:34:18
ok                       

In recipe TimeToday we discussed how to convert a date structure to a string. Convert in the opposite direction is also possible, and useful. Unfortunately, there is not a lot of built-in Erlang plumbing to do so. However, if we are very sure of the format we can easily extract the data we need using Erlang's ever-helpful io and io_lib modules:

5> Some_Date_String = "2004-04-26T18:26:18-0500".
"2004-04-26T18:26:18-0500".
6> {ok, [YYY,MMM,DD,HH,MM,SS,ZZ],_} = 
6> io_lib:fread("~4d-~2d-~2dT~2d:~2d:~2d-~4d", Some_Date_String).
{ok,[2004,4,26,18,26,18,500],[]}