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<?php $pattern="/\(((?>[^()]+)|(?R))*/\)"; //$str="(def a (x) (+ 1 x))(print (a 1))"; $str="(aaa)"; preg_match_all($pattern,$str,$out); var_dump($out);
Output for 5.2.3 - 5.6.28, 7.0.0 - 7.1.0
Warning: preg_match_all(): Unknown modifier '\' in /in/f5ZYH on line 9 NULL
Output for hhvm-3.10.0 - 3.12.0
Warning: Unknown modifier '\': [/\(((?>[^()]+)|(?R))*/\)] in /in/f5ZYH on line 9 NULL
Output for 5.2.0 - 5.2.2
<br /> <b>Warning</b>: preg_match_all() [<a href='function.preg-match-all'>function.preg-match-all</a>]: Unknown modifier '\' in <b>/in/f5ZYH</b> on line <b>9</b><br /> NULL
Output for 4.4.3 - 5.1.6
<br /> <b>Warning</b>: preg_match_all() [<a href='function.preg-match-all'>function.preg-match-all</a>]: Unknown modifier '\' in <b>/in/f5ZYH</b> on line <b>9</b><br /> array(0) { }
Output for 4.3.11 - 4.4.2
<br /> <b>Warning</b>: preg_match_all(): Unknown modifier '\' in <b>/in/f5ZYH</b> on line <b>9</b><br /> array(0) { }
Output for 4.3.0 - 4.3.10
<br /> <b>Warning</b>: Unknown modifier '\' in <b>/in/f5ZYH</b> on line <b>9</b><br /> array(0) { }