# 23 nothing is so as it seems, but why - Thread: https://externals.io/message/21578 - Original archive: https://news-web.php.net/php.internals/21578 - Started by Marco Kaiser on 2006-01-19T16:41:17+00:00 - Messages: 10 - Reply by email to internals@lists.php.net - More for agents: search with https://externals.io/search.md?q={query} · JSON API at https://externals.io/api · documentation at https://externals.io/llms.txt --- ## #21578 — Marco Kaiser — 2006-01-19T16:41:17+00:00 URL: https://externals.io/message/21578#21578 Today during a session i had a strange "magic" feature found in php. this works perfect as expected. it returns 22. but if i assign $a as a ref. to another variable it will be return 23. this will gave me to 23 (used the $b to the pre post stuff) this just happens if i have a ref. count to my var. WHY? :) http://en.wikipedia.org/wiki/23_%28film%29 -- Marco Kaiser --- ## #21579 — Hartmut Holzgraefe — 2006-01-19T16:48:11+00:00 URL: https://externals.io/message/21578#21579 · In reply to: #21578 Marco Kaiser wrote: > Today during a session i had a strange "magic" feature found in php. > > $a = 10; > echo ++$a + $a++; > ?> there is a very simple rule that PHP inherited from C: never use pre- and postfix increment operators in the same expression as the results are undefined -- Hartmut Holzgraefe, Senior Support Engineer . MySQL AB, www.mysql.com --- ## #21581 — Christian Schneider — 2006-01-19T17:04:03+00:00 URL: https://externals.io/message/21578#21581 Etienne Kneuss wrote: > Notice that this behavior can be reproduced using only prefix increment > operators. > > Is that also expected to give undefined results ? Yes, see - Chris --- ## #21582 — Marcus Boerger — 2006-01-19T19:53:58+00:00 URL: https://externals.io/message/21578#21582 · In reply to: #21578 Hello Marco, though Hartmut is perfectly correct in his statement here's what happens: $a = 10; // 10 ++$a // 11 $a + $a // 22 $a++ // 23 Thursday, January 19, 2006, 5:41:17 PM, you wrote: > Today during a session i had a strange "magic" feature found in php. > $a = 10; > echo ++$a + $a++; ?>> just to verfiy echo $a after your echo line, it will show 12 > this works perfect as expected. it returns 22. > but if i assign $a as a ref. to another variable it will be return 23. > $a = 10; > $b = &$a; > echo ++$a + $a++; ?>> > this will gave me to 23 > (used the $b to the pre post stuff) > $a = 10; > $b = &$a; > echo ++$b + $b++; ?>> > this just happens if i have a ref. count to my var. WHY? :) > http://en.wikipedia.org/wiki/23_%28film%29 > -- > Marco Kaiser Best regards, Marcus --- ## #21583 — Marco Kaiser — 2006-01-19T20:09:45+00:00 URL: https://externals.io/message/21578#21583 · In reply to: #21582 Hmm yes i know this, but its very interesting for me to see how php internaly handles ++$a with a pointer. Now i understand it :) -- Marco 2006/1/19, Marcus Boerger : > > Hello Marco, > > though Hartmut is perfectly correct in his statement here's what > happens: > > $a = 10; // 10 > ++$a // 11 > $a + $a // 22 > $a++ // 23 > > Thursday, January 19, 2006, 5:41:17 PM, you wrote: > > > […] > > > […] > ?>> > > just to verfiy echo $a after your echo line, it will show 12 > > > […] > > > […] > ?>> > > > […] > > > […] > ?>> > > > […] > > > […] > > > […] > > > > Best regards, > Marcus > > -- Marco Kaiser --- ## #21584 — Jani Taskinen — 2006-01-19T20:42:54+00:00 URL: https://externals.io/message/21578#21584 · In reply to: #21583 For the 2nd time: references ARE NOT POINTERS! :-p --Jani > Hmm yes i know this, > but its very interesting for me to see how php internaly handles ++$a with a > pointer. > Now i understand it :) > > -- Marco > > 2006/1/19, Marcus Boerger : > > […] > > > -- > Marco Kaiser > -- Give me your money at @ Donating money may make me happier and friendlier for a limited period! Death to all 4 letter abbreviations starting with P! --- ## #21585 — Marco Kaiser — 2006-01-19T20:45:26+00:00 URL: https://externals.io/message/21578#21585 · In reply to: #21584 Sorry Jani, i mean a reference (alias) :) -- Marco 2006/1/19, Jani Taskinen : > > > For the 2nd time: references ARE NOT POINTERS! :-p > > --Jani > > > > > > […] > with a > > […] > > -- > Give me your money at @ > Donating money may make me happier and friendlier for a limited period! > Death to all 4 letter abbreviations starting with P! > -- Marco Kaiser --- ## #21587 — Jon Dowland — 2006-01-20T11:36:01+00:00 URL: https://externals.io/message/21578#21587 · In reply to: #21578 > Today during a session i had a strange "magic" feature found in php. > > $a = 10; > echo ++$a + $a++; > ?> > > this works perfect as expected. it returns 22. Odd, I expected 21: echo (11 + 10) a = a + 1 -- Jon Dowland http://alcopop.org/ --- ## #21588 — Carl P. Corliss — 2006-01-20T15:14:16+00:00 URL: https://externals.io/message/21578#21588 · In reply to: #21587 Jon Dowland wrote: > > > > […] > > > Odd, I expected 21: > echo (11 + 10) > a = a + 1 > nope - discounting the 'undefined behavior' of using pre/post increment operators, 22 would be the correct assumption - remember, broken into seperate statements, it's effectively: $a = 10; $a = $a + 1; // $a == 11 $a + $a; // $a == 22 echo $a; $a = $a + 1; // $a == 23 Cheers, -- Carl --- ## #21590 — Andi Gutmans — 2006-01-20T16:47:28+00:00 URL: https://externals.io/message/21578#21590 · In reply to: #21588 Guys, please take this offlist. Undefined means undefined. There's no assumed way of it working. Andi At 07:14 AM 1/20/2006, Carl P. Corliss wrote: >Jon Dowland wrote: > > […] > >nope - discounting the 'undefined behavior' of using pre/post >increment operators, 22 would be the correct assumption - remember, >broken into seperate statements, it's effectively: > >$a = 10; >$a = $a + 1; // $a == 11 >$a + $a; // $a == 22 > >echo $a; > >$a = $a + 1; // $a == 23 > > >Cheers, > >-- >Carl