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<?php function is_cyclic(array &$array) { $lastKey = array_key_last($array); if ($lastKey === null) { // Array is empty return false; } static $marker; if ($marker === null) { $marker = new stdClass(); } if ($array[$lastKey] === $marker) { return true; } $array[] = $marker; foreach ($array as &$item) { if (is_array($item) && is_cyclic($item)) { array_pop($array); return true; } } array_pop($array); return false; } // Contains reference to itself $v = [1, 2, 3]; $v[1] = &$v; // Contains nested array with reference to $x $x = [1, [2, 3]]; $x[1][1] = &$x; // Contains nested array with reference to an ancestor $y = [1, [2, [3, 4]]]; $y[1][1][1] = &$y[1]; // Nested array contains reference to itself $z = [1, [2, 3]]; $z[1][1] = &$z[1]; // This array is not recursive $p = [1, 2, [3, 4, [5, 6, 7]]]; foreach (['v', 'x', 'y', 'z', 'p'] as $var) { $arr = &${$var}; echo "Array \$$var | Cyclic: "; var_export(is_cyclic($arr)); echo "\n"; echo "----------------\n"; var_dump($arr); echo "\n\n"; }
Output for 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.4, 8.3.6
Array $v | Cyclic: true ---------------- array(3) { [0]=> int(1) [1]=> *RECURSION* [2]=> int(3) } Array $x | Cyclic: true ---------------- array(2) { [0]=> int(1) [1]=> array(2) { [0]=> int(2) [1]=> *RECURSION* } } Array $y | Cyclic: true ---------------- array(2) { [0]=> int(1) [1]=> &array(2) { [0]=> int(2) [1]=> array(2) { [0]=> int(3) [1]=> *RECURSION* } } } Array $z | Cyclic: true ---------------- array(2) { [0]=> int(1) [1]=> &array(2) { [0]=> int(2) [1]=> *RECURSION* } } Array $p | Cyclic: false ---------------- array(3) { [0]=> int(1) [1]=> int(2) [2]=> array(3) { [0]=> int(3) [1]=> int(4) [2]=> array(3) { [0]=> int(5) [1]=> int(6) [2]=> int(7) } } }
Output for 8.3.5
Warning: PHP Startup: Unable to load dynamic library 'sodium.so' (tried: /usr/lib/php/8.3.5/modules/sodium.so (libsodium.so.23: cannot open shared object file: No such file or directory), /usr/lib/php/8.3.5/modules/sodium.so.so (/usr/lib/php/8.3.5/modules/sodium.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0 Array $v | Cyclic: true ---------------- array(3) { [0]=> int(1) [1]=> *RECURSION* [2]=> int(3) } Array $x | Cyclic: true ---------------- array(2) { [0]=> int(1) [1]=> array(2) { [0]=> int(2) [1]=> *RECURSION* } } Array $y | Cyclic: true ---------------- array(2) { [0]=> int(1) [1]=> &array(2) { [0]=> int(2) [1]=> array(2) { [0]=> int(3) [1]=> *RECURSION* } } } Array $z | Cyclic: true ---------------- array(2) { [0]=> int(1) [1]=> &array(2) { [0]=> int(2) [1]=> *RECURSION* } } Array $p | Cyclic: false ---------------- array(3) { [0]=> int(1) [1]=> int(2) [2]=> array(3) { [0]=> int(3) [1]=> int(4) [2]=> array(3) { [0]=> int(5) [1]=> int(6) [2]=> int(7) } } }
Output for 7.3.0 - 7.3.33, 7.4.0 - 7.4.33
Array $v | Cyclic: true ---------------- array(3) { [0]=> int(1) [1]=> &array(3) { [0]=> int(1) [1]=> *RECURSION* [2]=> int(3) } [2]=> int(3) } Array $x | Cyclic: true ---------------- array(2) { [0]=> int(1) [1]=> array(2) { [0]=> int(2) [1]=> &array(2) { [0]=> int(1) [1]=> *RECURSION* } } } Array $y | Cyclic: true ---------------- array(2) { [0]=> int(1) [1]=> &array(2) { [0]=> int(2) [1]=> array(2) { [0]=> int(3) [1]=> *RECURSION* } } } Array $z | Cyclic: true ---------------- array(2) { [0]=> int(1) [1]=> &array(2) { [0]=> int(2) [1]=> *RECURSION* } } Array $p | Cyclic: false ---------------- array(3) { [0]=> int(1) [1]=> int(2) [2]=> array(3) { [0]=> int(3) [1]=> int(4) [2]=> array(3) { [0]=> int(5) [1]=> int(6) [2]=> int(7) } } }
preferences:
131.33 ms | 403 KiB | 150 Q