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<?php var_dump( substr_count ('haystack', 'tack', 0, 0), substr('haystack', 0, 0) );
based on 3B2Ct
Output for 7.1.5 - 7.1.20, 7.2.0 - 7.2.33, 7.3.16 - 7.3.24, 7.4.0 - 7.4.13, 8.0.0
int(0) string(0) ""
Output for 7.1.0
int(1) string(0) ""
Output for 5.6.0 - 5.6.28, 7.0.0 - 7.0.20
Warning: substr_count(): Length should be greater than 0 in /in/bAu27 on line 4 bool(false) string(0) ""