Question

I would like to return the local time as string but with leading zeros. I tried this:

{{Year, Month, Day}, {Hour, Minute, Second}} = erlang:localtime().
DateAsString = io_lib:format("~2.10.0B~2.10.0B~4.10.0B~2.10.0B~2.10.0B~2.10.0B", 
           [Month, Day, Year, Hour, Minute, Second]).

But if some of the components is one digit, the returned string is:

[["0",57],"29","2011","17","33","34"]

The current month 9 is printed as ["0",57].

Please, help.

Thank you.

Answer 1

Try:

1> lists:flatten([["0",57],"29","2011","17","33","34"]).
"09292011173334"

io_lib:format/2 (and it’s companion io:format/2) actually returns a deep IO list. Such a list is printable and can be sent on a socket or written to a file just as a flat string, but is more efficient to produce. Flattening is often useless, because in all cases where the string will be printed or output to a file/socket it will automatically be flattened by Erlang.