I thought that adding something to a pointer always adds 1 sizeof(byte) to it. So if something is added to a pointer the compiler looks the sizeof the (typed) pointer points to? Ok, that makes some sense, but I did not know it before. In the past with the turbopascal compiler and other always sizeof byte was added. Thank you and regards, Rainer
Am Thursday 11 February 2010 17:36:04 schrieb Frank Peelo: > 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? I did not test it, but I think you are right. > 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 ) ); > > _______________________________________________ > > fpc-pascal maillist - fpc-pascal@lists.freepascal.org > > http://lists.freepascal.org/mailman/listinfo/fpc-pascal > > _______________________________________________ > fpc-pascal maillist - fpc-pascal@lists.freepascal.org > http://lists.freepascal.org/mailman/listinfo/fpc-pascal _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
