Question

Given a string that may contain any character (including a unicode characters), how can I convert this string into hexadecimal representation, and then reverse and obtain from hexadecimal this string?

Answer 1

Use pack() and unpack():

function hex2str($hex) {
  return pack('H*', $hex);
}

function str2hex($str) {
  $unpacked = unpack('H*', $str);
  return array_shift($unpacked);
}

$txt = 'This is test';
$hex = str2hex($txt);
$str = hex2str($hex);

echo "{$txt} => {$hex} => {$str}\n";

would produce

This is test => 546869732069732074657374 => This is test