SQL & PL/SQL

I am trying to get the maximum length a variable can be in a PL/SQL procedure.

I do not hard code my datatypes, I am using database columns to do this for me. My columns do not change often but it is possible and can be done without warning. What I want to do is take a substring of the source column dynamically.

Source Column 32
Target Column 30
Variable_Name Targetcolumn%TYPE

Variable_Name := substr(Source Column, 1, MaxLengthOfTargetColumn);

I repeat that I do not want to hard code in the length of the target column into the substring. Is there any way to do this?

Thanks in Advance.