So you're allowed add an integer to an untyped pointer?!

Wow!

Usually if you add 1 to a pointer of type t, then sizeof(t) gets added to the value of the pointer. So if p points at an array of byte, p+1 would point at the next element of the array, 1 byte after p. But if p points at an array of LongInt, then the next element is 4 bytes on from p, so adding 1 to p increases p by 4. So what would sizeof(pointer^) be?

To me, adding an integer to an untyped pointer feels undefined (i.e. I haven't studied the spec for it but I wouldn't have expected the compiler to do anything sensible with it) because what pointer points to is undefined and sizeof(something undefined) is not defined. So I haven't tried that myself.

From your code, I'm guessing that adding 1 to an untyped pointer adds 1 to the address. So ppp + http.header_anz would be http.header_anz bytes after ppp.

But http.pdata + http.header_anz means to add http.header_anz to a variable of type pointer to tchararr. That means, imagine http.pdata is pointing to an array[0..lots] of tcharrarr, find the address of element http.header_anz of that array. Now, tcharrarr is 1000 bytes long, so I would expect http.pdata + http.header_anz to be 1000*http.header_anz bytes after http.pdata.

Is that what you are seeing?

FP


On 11/02/2010 15:38, Rainer Stratmann wrote:
What is the difference between A* and B*?
regards, Rainer


type
 tchararr = array[ 0..999 ] of char;
 pchararr = ^tchararr;
http_obj = object pdata : pchararr; header_anz : longint;
  content_anz       : longint;
 end;

var
 http : http_obj;
 ppp : pointer;


 // This works for me A*
 ppp := http.pdata;
 ppp := ppp + http.header_anz;
 // This is not working B*
 ppp := http.pdata + http.header_anz;


 write( 'IP-Adress = ' + parse_ip( ppp , http.content_anz ) );
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