note 110314 added to function.unset

The combination of "global" and "unset" in functions can lead to some unexpected results. This is because the "global" function creates a reference to a variable at the time it's executed, so a variable can be deleted out from under a "global $my_variable" declaration in a function. Accessing data that's been deleted with an obsolete reference is usually a bad thing; in some languages it can generate a machine address fault. <?php $my_global_var = "old data"; f1(); function f1() // example of invalid variable reference use { global $my_global_var; // creates reference to global variable f2(); // recreates global variable, so reference is now invalid // bad... echo $my_global_var; // outputs "old data" (from invalid memory???) // good... global $my_global_var; // reestablish reference to new global variable echo $my_global_var; // outputs "new data" as expected } function f2() // recreate global variable { unset($GLOBALS['my_global_var']); // this syntax works with all variable types including arrays global $my_global_var; // must do this after unset to access new global variable $my_global_var = "new data"; } ?> ---- Server IP: 69.147.83.199 Probable Submitter: 72.201.124.170 ---- Manual Page -- http://www.php.net/manual/en/function.unset.php Edit -- https://master.php.net/note/edit/110314 Del: integrated -- https://master.php.net/note/delete/110314/integrated Del: useless -- https://master.php.net/note/delete/110314/useless Del: bad code -- https://master.php.net/note/delete/110314/bad+code Del: spam -- https://master.php.net/note/delete/110314/spam Del: non-english -- https://master.php.net/note/delete/110314/non-english Del: in docs -- https://master.php.net/note/delete/110314/in+docs Del: other reasons-- https://master.php.net/note/delete/110314 Reject -- https://master.php.net/note/reject/110314 Search -- https://master.php.net/manage/user-notes.php