Help pcre subpattern

[mengo]

hello,you all.

 

there is a problem let me not understand.i have a few codes like this:

         $pattern = "/b©(d)\2efgh/";
         $subject = "abcddefghijk";
         preg_match_all($pattern, $subject, $matches);
         echo "<pre>";
         print_r($matches);
         echo "</pre>";

 

i want to use var $pattern capture str "bcddefgh" in var $subject with "\2" back reference,but the result is not what i want,it ouputs nothing but an empty array. i think i did nothing wrong, in php manual, it says a backslash followed by a non-0 number can represent a back reference.but why it fails?

 

is there something wrong with  my codes or an error in php manual? is there some other problems in php.ini or somewhere else?

 

help, thanks!!

 

 

[web_craftsman]

What is this - ©  in your pattern ?

 

From what i have understood you try write {1,2}\1 instead of \2

Edited July 11, 2013 by web_craftsman

[mengo]

value of $pattern is not important ,it can also be replaced by "/(b)c(d)\2efgh/",i don't know why  an error occurs when i try to edit the first subpattern,maybe this value is better.

why "\2" can't reference the second subpattern "(d)"?

thanks!

Edited July 11, 2013 by mengo

[requinix]

"\2" == chr(2)

Escape the \ or use single quotes.

[mengo]

thank you for your help! I found another weird problem,for example:

$pattern = "/(1)(2)(3)(4)(5)(6)(7)((9)\3fgh/";
$subject = "1234567893fghijk";
preg_match_all($pattern, $subject, $matches);
echo "<pre>";
print_r($matches);
echo "</pre>";
echo chr(2);

form \1 to \7, no matter whick back reference is used, there will always get not correct result! But when changed to \8 or \9, if there is a respondding matching substring in variable $subject,while it will get correct result. Where there is a difference between these two conditions?

[requinix]

"\3" == chr(3)

Are you seeing the pattern?

 

[edit] "\nnn" for n=0-7 is the escape for a character in octal.

Edited July 11, 2013 by requinix

[mengo]

now it is clear! really thanks!

may be i should spend some time studying pattern more carefully!

[requinix]

Strings, actually.

 

http://www.php.net/manual/en/language.types.string.php

Edited July 11, 2013 by requinix

[mengo]

yes,thanks for your advice! both of them!