Hello everyone,
I am puzzled at PHP's handling of regex. Here's the code:
<?php
$str="aabcc";
$pattern="/((a+)b?(c+))/";
preg_match_all( $pattern,$str,$ matches);
print_r($matche s[0]);
?>
The behaviour I expect from the above would be to match:
a
aa
c
cc
abc
aabc
abcc
aabbcc
The output is ALWAYS the maximum strings :
Array
(
[0] =Array
(
[0] =aabcc
)
[1] =Array
(
[0] =aabcc
)
[2] =Array
(
[0] =aa
)
[3] =Array
(
[0] =cc
)
)
Any idea why the substrings are not picked up?
Thanks
Patrick 10 2107
..oO(Patrick Drouin)
>I am puzzled at PHP's handling of regex. Here's the code:
<?php
$str="aabcc" ; $pattern="/((a+)b?(c+))/";
preg_match_all ($pattern,$str, $matches); print_r($match es[0]);
?>
The behaviour I expect from the above would be to match: a aa c cc abc aabc abcc aabbcc
Nope. What's returned is the entire matched string and all parenthesized
sub strings (if there are any), but not every single matching point from
during the execution.
>The output is ALWAYS the maximum strings :
Correct.
>Array (
[0] =Array
(
[0] =aabcc
)
[1] =Array
(
[0] =aabcc
)
[2] =Array
(
[0] =aa
)
[3] =Array
(
[0] =cc
)
)
Any idea why the substrings are not picked up?
The above is exactly what you told preg_match() to return:
0: the entire matched string
1: the first sub pattern: ((a+)b?(c+)) =the entire string again
2: the second sub pattern: (a+) =aa
3: the third sub pattern: (c+) =cc
Micha
Hello Michael,
Nope. What's returned is the entire matched string and all parenthesized
sub strings (if there are any), but not every single matching point from
during the execution.
The above is exactly what you told preg_match() to return:
Well OK, let me rephrase then, how can I tell PHP to match the
substrings. In my mind, (a+) means a, aa, aaa, ... and not only the
maximum string. I don't see how that behaviour is logical in any way.
Thanks,
Patrick
Patrick Drouin wrote:
$pattern="/((a+)b?(c+))/";
$pattern="/(a+)b?(c+)/";
HTH
--
Toby A Inkster BSc (Hons) ARCS
[Geek of HTML/SQL/Perl/PHP/Python/Apache/Linux]
[OS: Linux 2.6.17.14-mm-desktop-9mdvsmp, up 10 days, 21:10.]
Sharing Music with Apple iTunes http://tobyinkster.co.uk/blog/2007/1...tunes-sharing/
On Mon, 17 Dec 2007 17:03:19 +0100, Patrick Drouin <no**@none.comw rote:
Hello everyone,
I am puzzled at PHP's handling of regex. Here's the code:
<?php
$str="aabcc";
$pattern="/((a+)b?(c+))/";
preg_match_all( $pattern,$str,$ matches);
print_r($matche s[0]);
?>
The behaviour I expect from the above would be to match:
a
aa
c
cc
abc
aabc
abcc
aabbcc
Is this one string or a set of strings you're trying to match? Only the
5th, 6th and 7th line will match this pattern...
>
The output is ALWAYS the maximum strings :
What do you mean by 'maximum'? I see nothing weird here...
--
Rik Wasmus
Hello,
On 18 déc, 05:34, Toby A Inkster <usenet200...@t obyinkster.co.u k>
wrote:
Patrick Drouin wrote:
$pattern="/((a+)b?(c+))/";
$pattern="/(a+)b?(c+)/";
If you try this, you will see that it spit out
[0] =aaabccc
[0] =aaa
[0] =ccc
That's not what I'm looking for...
Thanks,
P
Hello Rick,
On 18 déc, 06:52, "Rik Wasmus" <luiheidsgoe... @hotmail.comwro te:
<?php
$str="aabcc";
$pattern="/((a+)b?(c+))/";
preg_match_all( $pattern,$str,$ matches);
print_r($matche s[0]);
?>
The behaviour I expect from the above would be to match:
a
aa
c
cc
abc
aabc
abcc
aabbcc
The output is ALWAYS the maximum strings :
What do you mean by 'maximum'? I see nothing weird here...
OK,what I don't understand is why "a" is not captured as (a+) means
"a" or repeated "a"...
Thanks,
P
On Tue, 18 Dec 2007 15:31:14 +0100, Moi <pa************ @gmail.comwrote :
Hello Rick,
On 18 déc, 06:52, "Rik Wasmus" <luiheidsgoe... @hotmail.comwro te:
<?php
$str="aabcc";
$pattern="/((a+)b?(c+))/";
preg_match_all( $pattern,$str,$ matches);
print_r($matche s[0]);
?>
The behaviour I expect from the above would be to match:
a
aa
c
cc
abc
aabc
abcc
aabbcc
The output is ALWAYS the maximum strings :
What do you mean by 'maximum'? I see nothing weird here...
OK,what I don't understand is why "a" is not captured as (a+) means
"a" or repeated "a"...
because /(a+)b?(c+)/ means:
At least one or more a
Optionally followed by one b
Followed by at least one or more c
If 'a' is taken as a single string, it will not match because there's no c
after it, if it was part of a total string you gave us above, it will
still not match because both 'a' and 'aa' are not followed by 'c' or ('b'
and some 'c's), they're followed by a newline character (\n).
--
Rik Wasmus
Thanks Rik, I guess that makes sense.
P
..oO(Patrick Drouin)
>Hello Michael,
>Nope. What's returned is the entire matched string and all parenthesized sub strings (if there are any), but not every single matching point from during the execution.
The above is exactly what you told preg_match() to return:
Well OK, let me rephrase then, how can I tell PHP to match the substrings. In my mind, (a+) means a, aa, aaa, ... and not only the maximum string. I don't see how that behaviour is logical in any way.
That's how regular expressions work in general. The only thing that you
can control in many regex engines is whether the engine should stop the
matching process after it has found a minimum match (ungreedy) or if it
should continue until the maximum length (greedy), which is usually the
default.
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-----Original Message-----
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