Need help in converting the clob to varchar in oracle, I have to use the varchar in case function of oracle

Need help in converting the clob to varchar in oracle, I have to use the
varchar in case function of oracle

I have a requirement where i have to fetch the data from the clob datatype
, convert to the varchar2, to make a pivot for oracle 10g.
i am using the following
select max(case when key='abc' then dbms_lob.substr(value) end ) as
data_abc from table.
if the value is less than 4000 the above query works fine but if it is
more than 4000 it shows and error of buffer limit. On reading few blogs i
came to know that dbms_lob.substr can handle only 4000 characters in sql
but can handle upto 32k in a pl/sql statement.
if I write a procedure and run it, it works fine. but i want to use it in
a function. below is my function : >
create or replace FUNCTION CLOBTOVARCHAR
RETURN varchar2 is out_attribute_var varchar2(32767) ;
BEGIN
FOR i IN (select attribute_Value from car_course_attribute where id=1547156)
LOOP
out_attribute_var := dbms_lob.substr(i.attribute_Value, 32000, 1);
END LOOP;
RETURN out_attribute_var;
EXCEPTION
WHEN OTHERS THEN
raise_application_error(-20001,'An error was encountered - '||SQLCODE||'
-ERROR- '||SQLERRM);
END CLOBTOVARCHAR;
If the data is small it works fine but if the data is bigger than 4k, it
gives same error back.
now I have two questions: 1) Am I doing right by converting the clob to
varchar2 as I want to get pivot 2) Is my function correct?