Use of "empty character constant?"

19 years ago by Matt W — view source

unread

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

19 years ago by Pierre — view source

unread

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

19 years ago by Matt W — view source

unread

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?"

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

19 years ago by Pierre — view source

unread

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

19 years ago by Matt W — view source

unread

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?"

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

19 years ago by Antony Dovgal — view source

unread

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

19 years ago by Matt W — view source

unread

Hi Antony,

----- Original Message -----
From: "Antony Dovgal"

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?

I don't know; was wondering the same thing. :-) But, that is what I saw on
http://lxr.php.net :-(

Matt

19 years ago by Antony Dovgal — view source

unread

Hi Antony,

----- Original Message -----
From: "Antony Dovgal"

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?

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

19 years ago by Matt W — view source

unread

Hi Antony,

----- Original Message -----
From: "Antony Dovgal"

Hi Antony,

----- Original Message -----
From: "Antony Dovgal"

'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 :-(

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

19 years ago by Antony Dovgal — view source

unread

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

19 years ago by Michael Wallner — view source

unread

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

19 years ago by Mike Dransfield — view source

unread

Michael Wallner wrote:

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 ''.

http://lxr.php.net/source/ZendEngine2/zend_operators.h#71

I think he is talking about this, it appears as '' on lxr