Utl_file.fseek

Question

Hi all,
I want to know about the procedure fseek in utl_file
I know that we can use this procedure to move back or forward in a file without closing and opening it
but what i cant get is how this works
say this is the example
declare
name varchar2(30);
f1 utl_file.file_type;
pos number;
begin
   f1 := utl_file.fopen('VIR','SEARCH.TXT','R');
   utl_file.fseek(f1,10);
       pos := utl_file.fgetpos(f1);
dbms_output.put_line ('SUCCESS Seek to abs offset 10, currect position is '||to_char(pos));          
   utl_file.fseek(f1,NULL,5);
       pos := utl_file.fgetpos(f1);
dbms_output.put_line ('SUCCESS Seek to relative offset 5, currect position is'||to_char(pos));
   utl_file.fseek(f1,10,5);
       pos := utl_file.fgetpos(f1);
dbms_output.put_line ('SUCCESS Seek to absolute 10 relative offset 5, currect position is'||to_char(pos));
   utl_file.fseek(f1,NULL,-5);
       pos := utl_file.fgetpos(f1);
dbms_output.put_line ('SUCCESS Seek to rel offset -5, currect position is '||to_char(pos));
   utl_file.fclose(f1);
end;
o/p is
SQL> /
SUCCESS Seek to abs offset 10, currect position is 10
SUCCESS Seek to relative offset 5, currect position is15
SUCCESS Seek to absolute 10 relative offset 5, currect position is10
SUCCESS Seek to rel offset -5, currect position is 5
PL/SQL procedure successfully completed.What i dont understand is when i am using both absolute and relative offset i.e abs = 10 and rel = 5
then why its current position is 10 when i thought it would be 15?
please correct me if i am wrong.
or does it not consider the relative offset when the absolute is given
What i am thinking is when absolute and relative offset in fseek is present then the position should be
absolute + relative.
when absolute is null and relative is present the position would be
current position +/- relative offset
and if relative offset is null and absolute is present the current position is
absolute offset
thanks

Answer 1

Although it is not explicitly stated in the documentation, I beleieve that fseek is an either or proposition. That is, you supply either absolute or relative position. If you supply both, then only the first parameter (absolute) is evaluated.
My guess would be that somewhere in the internals, the utl_file.fseek procedure calls the c function fseek which is defined as:
int fseek(FILE *stream, long offset, int whence);where whence is a constant defined in stdio.h as:
SEEK_SET  Set position equal to offset bytes.
SEEK_CUR  Set  position  to  current   location   plus
SEEK_END  Set position to EOF plus offset.So, in psuedo code
IF absolute_offset is not null then
   call c.fseek (filepointer, absolute_offset, SEEK_SET);
elsif relative_offset is not null then
      call c.fseek (filepointer, relative_offset, SEEK_CUR);
else
   do nothing
end if;John