# Use of "empty character constant?" - Thread: https://externals.io/message/24291 - Original archive: https://news-web.php.net/php.internals/24291 - Started by Matt W on 2006-07-08T09:12:26+00:00 - Messages: 12 - 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 --- ## #24291 — Matt W — 2006-07-08T09:12:26+00:00 URL: https://externals.io/message/24291#24291 Hi all, I'm a C newbie and just started experimenting with the PHP internals a couple weeks ago... A few days ago I noticed assignment/comparison of char variables to '' (nothing between single quotes) in, for example, the is_numeric_string function (zend_operators.h), snprintf.c, spprintf.c, etc. I don't understand what it's doing. :-/ The only references I can find are about "empty character constant" compiler errors, which is what happens if I try to use '' in the same way (VC++ Express). Though PHP compiles fine with these "constructs," so something must be special there? Sorry to bother the list with this if it's a general C thing that should be known and not PHP-code specific. But I've tried to figure it out on my own (which I have with other stuff so far :-)) and can't, so I'd appreciate it if someone can clue me in! Thanks, Matt --- ## #24292 — Pierre — 2006-07-08T09:17:54+00:00 URL: https://externals.io/message/24291#24292 · In reply to: #24291 > Hi all, > > I'm a C newbie and just started experimenting with the PHP internals a > couple weeks ago... A few days ago I noticed assignment/comparison of char > variables to '' (nothing between single quotes) in, for example, the > is_numeric_string function (zend_operators.h), snprintf.c, spprintf.c, etc. > I don't understand what it's doing. :-/ The only references I can find are > about "empty character constant" compiler errors, which is what happens if I > try to use '' in the same way (VC++ Express). Though PHP compiles fine with > these "constructs," so something must be special there? http://publications.gbdirect.co.uk/c_book/chapter5/character_handling.html Cheers, --Pierre --- ## #24293 — Matt W — 2006-07-08T09:50:00+00:00 URL: https://externals.io/message/24291#24293 · In reply to: #24292 Hi Pierre, Thanks for the reply, but where does that page talk about an EMPTY character constant? I pretty much understand character handling otherwise. :-) Thanks, Matt ----- Original Message ----- From: "Pierre" Subject: Re: [PHP-DEV] Use of "empty character constant?" > > > […] char > > […] etc. > > […] are > > […] if I > > […] with > > […] > > http://publications.gbdirect.co.uk/c_book/chapter5/character_handling.html > > Cheers, > --Pierre --- ## #24294 — Pierre — 2006-07-08T10:12:31+00:00 URL: https://externals.io/message/24291#24294 · In reply to: #24293 > Hi Pierre, > > Thanks for the reply, but where does that page talk about an EMPTY character > constant? I pretty much understand character handling otherwise. :-) Then I do not understand your question. Do you have the exact error/warning/notice? And some example code? --Pierre --- ## #24295 — Michael Wallner — 2006-07-08T10:47:19+00:00 URL: https://externals.io/message/24291#24295 · In reply to: #24291 Matt W wrote: > Hi all, > > I'm a C newbie and just started experimenting with the PHP internals > a couple weeks ago... A few days ago I noticed assignment/comparison > of char variables to '' (nothing between single quotes) in, for > example, the is_numeric_string function (zend_operators.h), > snprintf.c, spprintf.c, etc. I don't understand what it's doing. :-/ > I don't see what you're seeing and cannot find a single occurrence of ''. -- Michael --- ## #24296 — Matt W — 2006-07-08T10:48:03+00:00 URL: https://externals.io/message/24291#24296 · In reply to: #24294 Hi Pierre, :-O I was just going to give you an example from zend_operators.h, is_numeric_string() and guess what? It's the "correct" way that I thought it should be! I thought PHP 6 changed something, to where /* handle hex numbers */ if (length>=2 && str[0]=='0' && (str[1]=='x' || str[1]=='X')) { conv_base=16; } which is easy to understand :-) became if (length>=2 && str[0]=='' && (str[1]=='x' || str[1]=='X')) { conv_base=16; } BUT, I recently started looking at http://lxr.php.net so I could cross-reference, etc., instead of searching my local sources, and that's where I first saw this "change." It took you asking for an example for me to realize that LXR is the problem, screwing up the display of '0' ! (Though I *think* I saw it correctly in some places?) LOL, I can't believe it. I kinda thought, "Oh well, I just don't get it," but I'm glad I e-mailed before spending more time than I have trying to figure out what the empty char constant does! http://lxr.php.net/ident?i=is_numeric_string -- check out 12 lines into the function definition. :-/ Well, thanks for helping me get on the right track to "solving" this. The LXR thing needs fixing I guess. Matt ----- Original Message ----- From: "Pierre" Subject: Re: [PHP-DEV] Use of "empty character constant?" > > > […] character > > […] > > Then I do not understand your question. Do you have the exact > error/warning/notice? And some example code? > > --Pierre --- ## #24297 — Antony Dovgal — 2006-07-08T11:02:43+00:00 URL: https://externals.io/message/24291#24297 · In reply to: #24296 > Hi Pierre, > > :-O I was just going to give you an example from zend_operators.h, > is_numeric_string() and guess what? It's the "correct" way that I thought > it should be! I thought PHP 6 changed something, to where > > /* handle hex numbers */ > if (length>=2 && str[0]=='0' && (str[1]=='x' || str[1]=='X')) { > conv_base=16; > } > > which is easy to understand :-) became > > if (length>=2 && str[0]=='' && (str[1]=='x' || str[1]=='X')) { > conv_base=16; > } '0' became '' ? Why would _character_ 0 become nothing? -- Wbr, Antony Dovgal --- ## #24298 — Matt W — 2006-07-08T11:10:31+00:00 URL: https://externals.io/message/24291#24298 · In reply to: #24297 Hi Antony, ----- Original Message ----- From: "Antony Dovgal" > > > […] thought > > […] > > '0' became '' ? > Why would _character_ 0 become nothing? I don't know; was wondering the same thing. :-) But, that is what I saw on http://lxr.php.net :-( Matt --- ## #24300 — Antony Dovgal — 2006-07-08T11:17:38+00:00 URL: https://externals.io/message/24291#24300 · In reply to: #24298 > Hi Antony, > > ----- Original Message ----- > From: "Antony Dovgal" > > > > […] > thought > > […] > > I don't know; was wondering the same thing. :-) But, that is what I saw on > http://lxr.php.net :-( What do you mean "I saw on lxr"? I still don't understand a word.. -- Wbr, Antony Dovgal --- ## #24299 — Matt W — 2006-07-08T11:28:22+00:00 URL: https://externals.io/message/24291#24299 · In reply to: #24300 Hi Antony, ----- Original Message ----- From: "Antony Dovgal" > > > […] on > > […] > > What do you mean "I saw on lxr"? > I still don't understand a word.. Didn't you see my explanation in the e-mail you first replied to? :-) http://lxr.php.net/source/ZendEngine2/zend_operators.h#82 That's where I saw that " '0' became '' " The LXR code-cross-referencing thing wrongly displays '0' , which was the cause of my confusion. Matt --- ## #24306 — Antony Dovgal — 2006-07-10T11:10:54+00:00 URL: https://externals.io/message/24291#24306 · In reply to: #24299 > Didn't you see my explanation in the e-mail you first replied to? :-) > http://lxr.php.net/source/ZendEngine2/zend_operators.h#82 > > That's where I saw that " '0' became '' " The LXR code-cross-referencing > thing wrongly displays '0' , which was the cause of my confusion. Please report it to LXR developers: http://lxr.linux.no/ -- Wbr, Antony Dovgal --- ## #24305 — Mike Dransfield — 2006-07-10T11:16:47+00:00 URL: https://externals.io/message/24291#24305 · In reply to: #24295 Michael Wallner wrote: > Matt W wrote: > > […] > I don't see what you're seeing and cannot find a single occurrence of ''. > http://lxr.php.net/source/ZendEngine2/zend_operators.h#71 I think he is talking about this, it appears as '' on lxr