3v4l.org

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<?php var_dump( $conv = mb_convert_encoding( $bin = hex2bin("dc01d8020042"), "UTF-32", "UTF-16" ), mb_check_encoding($bin, "UTF-32"), bin2hex(mb_convert_encoding($conv, "UTF-16", "UTF-32")) );
Output for 8.1.0 - 8.1.31, 8.2.0 - 8.2.26, 8.3.0 - 8.3.15, 8.4.1 - 8.4.2
string(12) "??B" bool(false) string(12) "003f003f0042"
Output for 7.4.0 - 7.4.33, 8.0.1 - 8.0.30
string(8) "?B" bool(false) string(8) "003f0042"

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75.03 ms | 407 KiB | 5 Q