note 72203 added to language.references.spot

Hi, If you want to check if two variables are referencing each other (i.e. point to the same memory) you can use a function like this: <?php function same_type(&$var1, &$var2){ return gettype($var1) === gettype($var2); } function is_ref(&$var1, &$var2) { //If a reference exists, the type IS the same if(!same_type($var1, $var2)) { return false; } $same = false; //We now only need to ask for var1 to be an array ;-) if(is_array($var1)) { //Look for an unused index in $var1 do { $key = uniqid("is_ref_", true); } while(array_key_exists($key, $var1)); //The two variables differ in content ... They can't be the same if(array_key_exists($key, $var2)) { return false; } //The arrays point to the same data if changes are reflected in $var2 $data = uniqid("is_ref_data_", true); $var1[$key] =& $data; //There seems to be a modification ... if(array_key_exists($key, $var2)) { if($var2[$key] === $data) { $same = true; } } //Undo our changes ... unset($var1[$key]); } elseif(is_object($var1)) { //The same objects are required to have equal class names ;-) if(get_class($var1) !== get_class($var2)) { return false; } $obj1 = array_keys(get_object_vars($var1)); $obj2 = array_keys(get_object_vars($var2)); //Look for an unused index in $var1 do { $key = uniqid("is_ref_", true); } while(in_array($key, $obj1)); //The two variables differ in content ... They can't be the same if(in_array($key, $obj2)) { return false; } //The arrays point to the same data if changes are reflected in $var2 $data = uniqid("is_ref_data_", true); $var1->$key =& $data; //There seems to be a modification ... if(isset($var2->$key)) { if($var2[$key] === $data) { $same = true; } } //Undo our changes ... unset($var1->$key); } elseif (is_resource($var1)) { if(get_resource_type($var1) !== get_resource_type($var2)) { return false; } return ((string) $var1) === ((string) $var2); } else { //Simple variables ... if($var1!==$var2) { //Data mismatch ... They can't be the same ... return false; } //To check for a reference of a variable with simple type //simply store its old value and check against modifications of the second variable ;-) do { $key = uniqid("is_ref_", true); } while($key === $var1); $tmp = $var1; //WE NEED A COPY HERE!!! $var1 = $key; //Set var1 to the value of $key (copy) $same = $var1 === $var2; //Check if $var2 was modified too ... $var1 = $tmp; //Undo our changes ... } return $same; } ?> Although this implementation is quite complete, it can't handle function references and some other minor stuff ATM. This function is especially useful if you want to serialize a recursive array by hand. The usage is something like: <?php $a = 5; $b = 5; var_dump(is_ref($a, $b)); //false $a = 5; $b = $a; var_dump(is_ref($a, $b)); //false $a = 5; $b =& $a; var_dump(is_ref($a, $b)); //true echo "---\n"; $a = array(); var_dump(is_ref($a, $a)); //true $a[] =& $a; var_dump(is_ref($a, $a[0])); // true echo "---\n"; $b = array(array()); var_dump(is_ref($b, $b)); //true var_dump(is_ref($b, $b[0])); //false echo "---\n"; $b = array(); $b[] = $b; var_dump(is_ref($b, $b)); //true var_dump(is_ref($b, $b[0])); //false var_dump(is_ref($b[0], $b[0][0])); //true* echo "---\n"; var_dump($a); var_dump($b); ?> * Please note the internal behaviour of PHP that seems to do the reference assignment BEFORE actually copying the variable!!! Thus you get an array containing a (different) recursive array for the last testcase, instead of an array containing an empty array as you could expect. BenBE. ---- Server IP: 217.160.72.57 Probable Submitter: 217.93.216.166 ---- Manual Page -- http://www.php.net/manual/en/language.references.spot.php Edit -- https://master.php.net/note/edit/72203 Del: integrated -- https://master.php.net/note/delete/72203/integrated Del: useless -- https://master.php.net/note/delete/72203/useless Del: bad code -- https://master.php.net/note/delete/72203/bad+code Del: spam -- https://master.php.net/note/delete/72203/spam Del: non-english -- https://master.php.net/note/delete/72203/non-english Del: in docs -- https://master.php.net/note/delete/72203/in+docs Del: other reasons-- https://master.php.net/note/delete/72203 Reject -- https://master.php.net/note/reject/72203 Search -- https://master.php.net/manage/user-notes.php