Convert GMT datetime to local

Question

I have a datetime value in GMT timezone. How can I convert it to my local timezone? I would expect there to be a function for this. Please note that I can not just add or subtra

Answer 1

I made a function that would return the GMT offset, but when I compiled it, I got this error:

ERROR: Built-in SAS FUNCTION or SUBROUTINE already exists with name 'GMToff'.

It turns out, there is an undocumented function in SAS that returns the GMT offset and by luck I chose the same name! Here are some examples of usage. Anyways, it will not return the offset on a specific time, as I wanted, only for the current time. Here is a function that will convert the datetime to "local" time, given a timezone (only supports GMT, but adding additional timezones as needed should be trivial):

proc fcmp outlib = Apfmtlib.funksjoner.localtime;
function localtime(datetime,tz$);
    if upcase(tz)="GMT" then do;
      offset_normal=3600;
      offset_summer=7200;
    end;
    localtime=datetime+offset_normal;
    /*If datetime is between 1 AM the last Sunday of March and 1 AM the last Sunday of October it is "summertime" in central Europe:*/
    if intnx('week',mdy(3,31,year(datepart(datetime))),0)*86400 + 3600 le datetime le intnx('week',mdy(10,31,year(datepart(datetime))),0)*86400 + 3600 then localtime=datetime+offset_summer;;
    return(localtime);
endsub;
quit;
options cmplib = Apfmtlib.funksjoner;
/*Usage examples:*/
data _null_;
    gmtdatetime="17SEP14:09:42:10"dt;
    localdatetime=localtime(gmtdatetime,"GMT");
    put localdatetime datetime.;
    gmtdatetime="17DEC14:09:42:10"dt;
    localdatetime=localtime(gmtdatetime,"GMT");
    put localdatetime datetime.;
run;