Diff char in variable and procedure call

Question

I understand the difference between Char en Varchar. What I don't understand is the different behaviour of Char when assigning a plain variable and when assigning a procedure call variable. I've created this sample code:
declare
  v char;
  procedure t (i char) as
  begin
    if i = ' ' then
      dbms_output.put_line('ok');
    else
      dbms_output.put_line('else');
    end if;
  end;
begin
  v := '';
  t('');
  t(' ');
  t(null);
  t(v);
end;
else
ok
else
ok
PL/SQL-procedure is geslaagd.The first (t('')) call and last (t(v)) call I think should result in the same answer, but apearantly, when v is assigned, a space is passed into the variable (sounds correct according to documentation), but when i is directly assigned, a null is assigned, rather than a space.
Does anyone know what the explanation is for this behaviour?
Thanx,
Lennert
ps, I'm not looking for a solution or a work around, I'm just interested in the background.
pps, I'm running O8174 on HPUX

Answer 1

x CHAR;
It's default length is one but if you don't assign a value, it's value is null and its length is null. The empty string ('') is not null, so the assignment x := '' will assign a value of space, since PL/SQL pads with spaces to fill the length.
PROCEDURE test is
x char;
BEGIN
dbms_output.put_line('x = >' || x || '< , the length of x is: ' || to_char(length(x)));
x := null;
dbms_output.put_line('x = >' || x || '< , the length of x is: ' || to_char(length(x)));
x := '';
dbms_output.put_line('x = >' || x || '< , the length of x is: ' || to_char(length(x)));
dbms_output.put_line(to_char(ascii(x)));
x := ' ';
dbms_output.put_line('x = >' || x || '< , the length of x is: ' || to_char(length(x)));
END test;
SQL> execute test.proc1
x = >< , the length of x is:
x = >< , the length of x is:
x = > < , the length of x is: 1
32
x = > < , the length of x is: 1