Edit report at http://bugs.php.net/bug.php?id=54454&edit=1
ID: 54454
Updated by: pajoye@php.net
Reported by: zweibieren at yahoo dot com
Summary: substr_compare incorrectly reports equality in some
cases
-Status: Closed
+Status: Re-Opened
Type: Bug
Package: Strings related
Operating System: linux
PHP Version: Irrelevant
Assigned To: pierrick
Block user comment: N
Private report: N
New Comment:
Chris and Scott are seeing issues with this change. Reopening.
Previous Comments:
------------------------------------------------------------------------
[2011-04-03 09:23:04] pierrick@php.net
This bug has been fixed in SVN.
Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
Thank you for the report, and for helping us make PHP better.
------------------------------------------------------------------------
[2011-04-03 09:18:30] pierrick@php.net
Automatic comment from SVN on behalf of pierrick
Revision: http://svn.php.net/viewvc/?view=revision&revision=309910
Log: Fixed bug #54454 (substr_compare incorrectly reports equality in
some cases)
------------------------------------------------------------------------
[2011-04-02 23:52:11] zweibieren at yahoo dot com
Description:
------------
---
From manual page:
http://www.php.net/function.substr-compare#Description
<blockquote>
int substr_compare ( string $main_str , string $str , int $offset , int
$length ... )
substr_compare() compares main_str from position offset with str up to
length characters.
Return Values
Returns < 0 if main_str from position offset is less than str, > 0 if it
is greater than str, and 0 if they are equal. ...
</blockquote>
---
HOWEVER, if main_str is shorter than str, substr_compare checks only up
to the length of main_str. This is NOT how I read the description. I
believe the comparison should extend to length characters and render a
non-zero value if the two strings differ at any character in the first
length characters.
WORKAROUND: Use strncmp.
{Note that substr_compare advertises itself as "binary safe." Since it
is stopping at '\0', it fails to actually BE binary safe.}
Test script:
---------------
<html><head></head><body>
<?php echo 'four comparisons of "/" and "/asd":'
. '<br/> substr_compare("/", "/asd", 0, 4) => '
. substr_compare("/", "/asd", 0, 4)
. ' <b>(SHOULD BE -3)</b>'
. '<br/> substr_compare("/asd", "/", 0, 4) => '
. substr_compare("/asd", "/", 0, 4)
. '<br/> strncmp("/", "/asd", 4) => '
. strncmp("/", "/asd", 4)
. '<br/> strncmp("/asd", "/", 4) => '
. strncmp("/asd", "/", 4); ?>
</body></html>
Expected result:
----------------
four comparisons of "/" and "/asd":
substr_compare("/", "/asd", 0, 4) => -3
substr_compare("/asd", "/", 0, 4) => 3
strncmp("/", "/asd", 4) => -3
strncmp("/asd", "/", 4) => 3
Actual result:
--------------
four comparisons of "/" and "/asd":
substr_compare("/", "/asd", 0, 4) => 0 (SHOULD BE -3)
substr_compare("/asd", "/", 0, 4) => 3
strncmp("/", "/asd", 4) => -3
strncmp("/asd", "/", 4) => 3
As the script says, the first reported value should be -3.
------------------------------------------------------------------------
--
Edit this bug report at http://bugs.php.net/bug.php?id=54454&edit=1