Convert date format to character string - sas

Question

I have a column of format DATETIME23. like this:
14.02.2017 13:00:25
I want to conver it to a string, so later, i would be able to modern it, so, for example, the final version would look like:
2017-02-14 13:00:25.000
Problem occures, when i try to convert date to char format: in result i have a string of smth like 1802700293 - which is the number of seconds.
I tried:
format date $23.0
or
date = put(date, $23.0)
P.S This is nother try:
data a;
format d date9.;
d = '12jan2016'd;
dtms = cat(day(d),'-',month(d),'-',year(d),' 00:00:00.000');
/* если нужно обязательно двухзначные день и месяц, то такой колхоз: */
if day(d) < 10 then dd=cat('0',put(day(d),$1.));
else ddday=put(day(d),$2.);
if month(d) < 10 then mm=cat('0',put(month(d),$1.));
else mm=put(month(d),$2.);
yyyy=put(year(d),$4.);
/*dtms2 = cat(dd,'-',mm,'-',yyyy,' 00:00:00.000');*/
dtms2 = cat(dd,'-',mm,'-',yyyy,' 00:00:00.000');
dtms = cat(day(d),'-',month(d),'-',year(d),' 00:00:00.000');
run;
BUT, abnormally, the dtms2 concat destroys the zero in the month element

Answer 1

If your datetime is stored as a SAS datetime, just use the appropriate format :
data test ;
dt = '09feb2017:13:53:26'dt ; /* specify a datetime constant */
new_dt = put(dt,E8601DT23.3) ; /* ISO datetime format */
run ;
Output
dt new_dt
1802267606 2017-02-09T13:53:26.000
If you need to replace the 'T' with a space, simply add a translate function around the put().

Answer 2

For your dtms solution you can use put and the Z2. format to keep the leading zero when you concatenate:
dtms = cat(day(d),'-', put(month(d),z2.),'-',year(d),' 00:00:00.000');
You should be able to just use put(date, datetime23.) for your problem though instead of $23, which is converting the number of seconds to a string with length 23. However, as a comment has mentioned datetime23. is not the format from your example.