Hi folks,

here is something for the pros:

var p:^byte;

...

p^:=99;  {or any other byte}
writeln(mem[seg(p):ofs(p)]);  {Does not write 99!!}

Compiler TP 6, Real Mode, This occurs no mater if data word aligment is
switched on or off.

So, why???? And, of course, where stands my number?

Tomy

var p:^byte;
begin
  GetMem(p, sizeof(byte));
  p^:=99;  {or any other byte}
  Writeln(p^);
  FreeMem(p, sizeof(byte));
end.

 Remco de Korte wrote in article <3364B58C.3...@xs4all.nl>...

p^ := 99; {or any other byte}
writeln(Mem[seg(p^):ofs(p^)]); {Does write 99!!}

It's because Mem[seg(p):ofs(p)] will read the first byte of the variable p,
which is the pointer to the value 99.  So you're reading the value of p,
not the value that p is pointing to.

var p: ^byte

Begin
 New(p);
 p^ := 99;
 Writeln(mem[seg(p^):ofs(p^)]);
 Dispose(p);
End.

But try the following writeln, writeln(mem[seg(p^):ofs(p^)])
That makes pascal show the value AT that memory address (99)
--

On Mon, 28 Apr 1997 16:34:52 +0200, Remco de Korte

Let's take it from the top. (Most of what I'm going to write now you
already know. Just humor me, if you will.)

        var p: ^byte;

means P is a pointer to a byte somewhere in memory. Therefore, P
itself is a variable that contains an address pointing to whatever is
in P^.

        seg(p)

returns the segment of the variable P, NOT the segment of the byte
pointed to by the contents of P.

In a sense, you code should read:

        writeln(mem[seg(p^):ofs(p^)]);

except I don't think TP will be happy with that. Try it, if it works,
fine, if it doesn't, do it this way:

        var p: ^byte;
              a: array[0..1] of word;
        begin
                getmem(p,1);
                p^:=99;
                move(p,a,4);
                writeln(mem[a[1]:a[0]]);
                freemem(p,1)
        end.

Please let me know if this works out.

But, in answer to your question - you asked to display the byte at
"p".  I say again, you asked to display the low byte of the offset
of the memory location where the pointer "p" is located.  If you
want to use mem to access the 99 you stored, then you have to tell
seg and ofs that they are to use the location of the dereferenced
pointer and not the location of the pointer.

Try using  Mem[Seg(p^),Ofs(p^)]

Of course, as also mentioned, "writeln (p^);" will output "99".  Even
then, it's still a useful exercise to help explain how pointers work.
:-)

On 26 Apr 1997 07:38:47 GMT, Tomy_Neum...@t-online.de (Thomas Neumann)
wrote:

What you need is: WriteLn(mem[seg(p^):ofs(p^)]). Ofs(p^) returns the
offset of the memory-location "pointed" by the adress stored in p.

(I can explain it in german if you don't understand my very bad
english)

On 26 Apr 1997 07:38:47 GMT, Tomy_Neum...@t-online.de (Thomas Neumann)
wrote:

seg(p^):ofs(p^) should work (not sure !).

And : no, you're *not* stupid. This pointer {*word*99} can be very
irritating ...

On 26 Apr 1997, Thomas Neumann wrote:

var p:byte; { NOT pointer }
...
p:=99;
writeln (mem[seg(p):ofs(p)]);

Your code will give one byte of ADDRESS where number 99 is stored

writeln(mem[seg(p^):ofs(p^)]);

--

In article <3364BD8C.4...@bcoll.demon.co.uk> of Mon, 28 Apr 1997
16:09:00 in comp.lang.pascal.borland, Robert Smith <i94robertsmith@bcoll