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[2003-09-30 18:23 UTC] cdragon at draconic dot com
Description:
------------
Using extract($GLOBALS, EXTR_REFS); can cause the left hand side of two globals set "by-value" equal to one-another to become corrupted in the $GLOBALS array. Hard to explain in English, but easier to see in the code below.
Reproduce code:
---------------
$sortColumn = "Affinity";
// Using "$lastSortColumn = substr($sortColumn, 0);" fixes the bug
$lastSortColumn = $sortColumn;
print "sort=" . $GLOBALS['sortColumn'] . " lastsort=" . $GLOBALS['lastSortColumn'] . "<p>";
extractGlobs();
print "sort=" . $GLOBALS['sortColumn'] . " lastsort=" . $GLOBALS['lastSortColumn'] . "<p>";
function extractGlobs()
{
// Commenting out the line below fixes the bug. So does not using the EXTR_REFS flag.
extract($GLOBALS, EXTR_REFS);
}
Expected result:
----------------
sort=Affinity lastsort=Affinity
sort=Affinity lastsort=Affinity
Actual result:
--------------
sort=Affinity lastsort=Affinity
sort=Affinity lastsort=
or, randomly, you get an access violation instead:
PHP has encountered an Access Violation at 02CFF32F
(the 02CFF32F is variable)
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Last updated: Sat Oct 25 14:00:01 2025 UTC |
Well, thank you for your quick (but rude) response. It is certainly not useless (or stupid) to extract references to globals. Extracting them without using the REFS flag creates deep copies of every variable (if I understand things correctly), which is very wasteful of resources. More importantly, you can't modify the contents of a global string unless you extract with REFS or use an alternate method. For example: $var = "x"; extrTest(); print "var=$var<p>"; function extrTest() { extract($GLOBALS); //global $var; //extract($GLOBALS, EXTR_REFS); //$GLOBALS["var"] = "y"; $var = "y"; } Will print "var=x" instead of the desired "var=y" (which you can get using any of the commented-out lines). Since there are obviously other syntactic alternatives, I don't _have_ to use the REFS method. However, I would certainly consider it a serious bug that you can cause PHP to access violation and exhibit randomish, hard to diagnose errors by doing something that actually _works most of the time_, serves a valid purpose, seems like it should work (without knowing some things about PHP's inner workings), and is not even cautioned against anywhere in the documentation that I can find.