Varchar2 size as return code or output parameter ?

Question

Hi everybody,
As far as i know , the limit size of a varchar2 is (4000) but it seems to be limited in my stored procedure to under then 255 caracteres. Does anyone have an ideas of what happen ?
When i execute the proc below, i get the first 200 caracteres when i change the value in the select SUBSTR(extract(msg_text,'/').getStringVal(),1,200) into chaine to select SUBSTR(extract(msg_text,'/').getStringVal(),1,255) into chaine , in my proc, i get an error message :
The following error has occurred:
ORA-06502: PL/SQL: numeric or value error: character string buffer too small
ORA-06512: at line 5
the msg_text colonne is a XMLTYPE column.
CREATE OR REPLACE function read_message(p_id_message IN NUMBER) RETURN VARCHAR2 AS
BEGIN
declare
chaine varchar2(4000);
begin
chaine := '';
dbms_output.enable(1000000);
select SUBSTR(extract(msg_text,'/').getStringVal(),1,200) into chaine
     from message
     where id_message= p_id_message ;
return chaine;
end;
END;
/

Answer 1

I think it doesn't have anything to do with the size.
From the docs
datatype Specify the datatype of the argument. An argument can have any
datatype supported by PL/SQL.
Datatypes cannot specify length, precision, or scale. For example, VARCHAR2(10) is
not valid, but VARCHAR2 is valid. Oracle derives the length, precision, and scale of
an argument from the environment from which the procedure is called.Cheers
Sarma.