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<?php $a = "1234567890"; var_dump($a["10"], isset($a["10"])); // false; 10進数の10として認識されている $a .= "a"; var_dump($a["10"], isset($a["10"])); // true
Output for 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.7
Warning: Uninitialized string offset 10 in /in/NQvXb on line 4 string(0) "" bool(false) string(1) "a" bool(true)
Output for 5.2.10 - 5.2.17, 5.3.0 - 5.3.29, 5.4.0 - 5.4.45, 5.5.0 - 5.5.38, 5.6.0 - 5.6.40, 7.0.0 - 7.0.33, 7.1.0 - 7.1.33, 7.2.0 - 7.2.33, 7.3.0 - 7.3.31, 7.4.0 - 7.4.25, 7.4.27 - 7.4.33
Notice: Uninitialized string offset: 10 in /in/NQvXb on line 4 string(0) "" bool(false) string(1) "a" bool(true)
Output for 7.3.32 - 7.3.33, 7.4.26
string(0) "" bool(false) string(1) "a" bool(true)
Output for 4.3.3 - 4.3.11, 4.4.0 - 4.4.9, 5.0.3 - 5.0.5, 5.1.1 - 5.1.6, 5.2.0 - 5.2.9
Notice: Uninitialized string offset: 10 in /in/NQvXb on line 4 string(0) "" bool(false) string(1) "a" bool(true)
Output for 5.1.0
Fatal error: fatal flex scanner internal error--end of buffer missed in /in/NQvXb on line 7
Process exited with code 255.
Output for 5.0.0 - 5.0.2
Notice: Uninitialized string offset: 10 in /in/NQvXb on line 4 string(0) "" bool(false) string(1) "a" bool(false)
Output for 4.3.0 - 4.3.2
Notice: Uninitialized string offset: 10 in /in/NQvXb on line 4 Notice: Uninitialized string offset: 10 in /in/NQvXb on line 4 string(0) "" bool(false) string(1) "a" bool(true)

preferences:
279.95 ms | 402 KiB | 458 Q