How to Convert from String to Date and from Date to String in Dynamics AX

We will read dates from  a table we will check if the date is null for that we will convert it to String using 'date2str'  to compare it with "".
Then we will declare a date and insert it into this table3. In that case we have to convert a String to date we use ' str2date'. And you can of course personnalize the Separators and Date Format when converting from date to string