Bug #75181 [Com]: PHP's PCRE API doesn't differentiate empty matches from non-matches

Edit report at https://bugs.php.net/bug.php?id=75181&edit=1 ID: 75181 Comment by: jocrutrisi at ibsats dot com Reported by: jocrutrisi at ibsats dot com Summary: PHP's PCRE API doesn't differentiate empty matches from non-matches Status: Not a bug Type: Bug Package: PCRE related Operating System: All PHP Version: 7.2.0RC1 Block user comment: N Private report: N New Comment: kelunik@php.net This flag is EXACTLY what was needed, excellent! But it's not documented on php.net yet, hence the report. Sorry for the noise :) Previous Comments: ------------------------------------------------------------------------ [2017-09-11 06:56:14] kelunik@php.net PREG_UNMATCHED_AS_NULL has been introduced in PHP 7.2 as a flag. See https://3v4l.org/bu1Sf#v720alpha1. ------------------------------------------------------------------------ [2017-09-11 06:28:44] spam2 at rhsoft dot net read the manual again and just check the return vlue2 ------------------------------------------------------------------------ [2017-09-11 05:23:28] jocrutrisi at ibsats dot com Description: ------------ PCRE differentiates "a sub-pattern that matched and is empty" from "a sub-pattern that didn't match". But in PHP's exposed APIs both of these cases produce a sub-pattern key with an empty match. Probably this can be a flag, for unfortunate B.C. reasons, but the current behavior is certainly not correct. Test script: --------------- $re = '%^ ((?=x))? ((?=y))? (\w) $%mx'; $str = 'x y z'; preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0); // Print the entire match result var_dump($matches); Expected result: ---------------- Observe the identical PCRE regex and input on Regex101, notice the flag "isParticipating" clearly points out which pattern matched (even if empty) or didn't match: [ [ { "content": "x", "isParticipating": true, "groupNum": 0, }, { "content": "", "isParticipating": true, "groupNum": 1, }, { "content": "", "isParticipating": false, "groupNum": 2, }, { "content": "x", "isParticipating": true, "groupNum": 3, } ], [ { "content": "y", "isParticipating": true, "groupNum": 0, }, { "content": "", "isParticipating": false, "groupNum": 1, }, { "content": "", "isParticipating": true, "groupNum": 2, }, { "content": "y", "isParticipating": true, "groupNum": 3, } ], [ { "content": "z", "isParticipating": true, "groupNum": 0, }, { "content": "", "isParticipating": false, "groupNum": 1, }, { "content": "", "isParticipating": false, "groupNum": 2, }, { "content": "z", "isParticipating": true, "groupNum": 3, } ] ] Source: https://regex101.com/r/N90TJE/1 Actual result: -------------- Both matching-and-empty and non-matching are just empty strings, we can't tell them apart: array(3) { [0]=> array(4) { [0]=> string(1) "x" [1]=> string(0) "" [2]=> string(0) "" [3]=> string(1) "x" } [1]=> array(4) { [0]=> string(1) "y" [1]=> string(0) "" [2]=> string(0) "" [3]=> string(1) "y" } [2]=> array(4) { [0]=> string(1) "z" [1]=> string(0) "" [2]=> string(0) "" [3]=> string(1) "z" } } ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=75181&edit=1