php.net |  support |  documentation |  report a bug |  advanced search |  search howto |  statistics |  random bug |  login

go to bug id or search bugs for

Bug #29427 preg_match offset not equivalent to substr
Submitted: 2004-07-28 13:29 UTC Modified: 2004-12-06 16:00 UTC
Votes:1
Avg. Score:5.0 ± 0.0
Reproduced:1 of 1 (100.0%)
Same Version:0 (0.0%)
Same OS:0 (0.0%)
From: x-g at monkeyblah dot com Assigned:
Status: Not a bug Package: PCRE related
PHP Version: 4.3.8 OS: Windows XP
Private report: No CVE-ID: None
View Developer Edit
Welcome back! If you're the original bug submitter, here's where you can edit the bug or add additional notes.
If you forgot your password, you can retrieve your password here.
Password:
Status:
Package:
Bug Type:
Summary:
From: x-g at monkeyblah dot com
New email:
PHP Version: OS:

 

 [2004-07-28 13:29 UTC] x-g at monkeyblah dot com 
Description:
------------
According to the manual, passing an offset to preg_match is equivalent to passing substr($string, $offset) to the function. This is not the case, however; regular expressions that match on beginning-of-string will not match if an offset is specified, but work fine if substr() is used in a supposedly equivalent manner.

Either this is a problem with regular expressions giving unexpected behaviour, or perhaps the manual just need to be changed to reflect the difference.


Reproduce code:
---------------
	$string = "abc def";
	if (preg_match("/^[a-zA-Z]+/", $string, $matches, 0, 4))
		echo "Matches\n";
	else
		echo "Does not match\n";
	if (preg_match("/^[a-zA-Z]+/", substr($string, 4), $matches, 0))
		echo "Matches\n";
	else
		echo "Does not match\n";

Expected result:
----------------
Matches
Matches


Actual result:
--------------
Does not match
Matches

Patches

Pull Requests

History

AllCommentsChangesGit/SVN commitsRelated reports
 [2004-08-16 05:35 UTC] skissane at iips dot mq dot edu dot au 
The behaviour the manual implies is far more useful for my application. This is because I need to repeatedly match the beginning of substrings, but using substr(...) results in excessive memory usage, especially when the strings are very large.

I would encourage this bug to be fixed ASAP.
 [2004-08-16 05:36 UTC] skissane at iips dot mq dot edu dot au 
Also, confirmed this bugs existence in PHP 5.0.0.
 [2004-12-06 16:00 UTC] tony2001@php.net 
Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

That's expected behaviour, because you're trying to match from the beginning of the string and using offset in the same time. 
Take a look at the example below.

Following 2 lines work:
preg_match("/[a-zA-Z]+/", $string, $matches, 0, 1)
preg_match("/[a-zA-Z]+/", substr($string, 1), $matches, 0)

and here second line will work:
preg_match("/^[a-zA-Z]+/", $string, $matches, 0, 1)
preg_match("/^[a-zA-Z]+/", substr($string, 1), $matches, 0)
 
PHP Copyright © 2001-2025 The PHP Group
All rights reserved. 		Last updated: Wed Jan 15 10:01:29 2025 UTC