Creating fixed field length records

[Len Morgan]

I'm trying to create some records to exchange data with another vendor's 
equipment.  The records have fixed field widths.  I'm sure that I saw 
somewhere that I could do something like:

put "20030501" into character 20 to 27 of myRecord

and if the string wasn't that long (yet), it would pad the string up to 
where I was inserting (i.e., char 20).  Just playing with this in the 
message box (using a global variable to build up the record), it gives 
me an error if I try to add characters that are beyond the current end 
of the string.

Did I misread something?  Do I need to create a string of 396 spaces 
(the length of this particular record) first and THEN put the characters in?

Thanks!

Len Morgan