How to Get the Correct Character Offset in UTF-8 Strings After a preg_match() with PREG_OFFSET_CAPTURE?

Get Multibyte Character Count Before Match with preg_match()

Problem:

When performing a regular expression match on a UTF-8 encoded string using preg_match() with the PREG_OFFSET_CAPTURE parameter, the resulting offset is calculated in bytes, not character count. This can be problematic when matching multibyte characters, as their byte length may differ from their character length.

For example, using the following code to match the "H" character in a UTF-8 encoded string, the resulting offset is 2, even though the character "H" is at index 1:

$str = "\xC2\xA1Hola!";
preg_match('/H/u', $str, $a_matches, PREG_OFFSET_CAPTURE);
echo $a_matches[0][1];

Resolution:

To obtain the correct character count offset, use mb_strlen() to determine the length of the substring up to the match:

$str = "\xC2\xA1Hola!";
preg_match('/H/u', $str, $a_matches, PREG_OFFSET_CAPTURE);
echo mb_strlen(substr($str, 0, $a_matches[0][1]));

This will calculate the offset in UTF-8 characters, providing the correct result.

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