3v4l.org

run code in 150+ php & hhvm versions
Bugs & Features
<?php preg_match('/b(?<a>a)?/', 'xxxxbxaxxx', $matches); var_dump($matches); var_dump(array_key_exists('a', $matches));
Output for 4.4.6 - 4.4.9, 5.2.2 - 5.6.28, hhvm-3.12.0, 7.0.0 - 7.1.0
array(1) { [0]=> string(1) "b" } bool(false)
Output for hhvm-3.10.0

Process exited with code 153.
Output for 5.2.0 - 5.2.1
Warning: preg_match(): Compilation failed: unrecognized character after (?< at offset 4 in /in/tr5a0 on line 3 NULL Warning: array_key_exists(): The second argument should be either an array or an object in /in/tr5a0 on line 7 bool(false)
Output for 4.3.11 - 4.4.5, 5.0.0 - 5.1.6
Warning: preg_match(): Compilation failed: unrecognized character after (?< at offset 4 in /in/tr5a0 on line 3 array(0) { } bool(false)
Output for 4.3.0 - 4.3.10
Warning: Compilation failed: unrecognized character after (?< at offset 4 in /in/tr5a0 on line 3 array(0) { } bool(false)