They are a Variable Construct That 'Points To' or Stores the Memory Address of Another Object.
Particularly Useful When Modelling Space Requirements Vary
STD TEXTIO Implimetation is an Example.
Example:
Example:
L Initially Contains the Value null Indicating It's Not Pointing to A Valid Location
begin
--if L /= NULL then
-- Deallocate(L);
--end if;
if not Endfile(f) then
READ(f, buf, len);
assert len <= MAX_LINE
report "Textio: Truncated input line greater than "
& Int_to_string(MAX_LINE)
& " characters."
severity ERROR;
end if;
if (len > 0) and (buf(len) = LF) then
len := len - 1;
end if;
L := new string'(buf(1 to len));
end;
type cell_ptr is access cell ;
type cell is record