How to replace/remove 4(+)-byte characters from a UTF-8 string in PHP?

Question

It seems like MySQL does not support characters with more than 3 bytes in its default UTF-8 charset.

So, in PHP, how can I get rid of all 4(-and-more)-byte characters in a string and replace them with something like by some other character?

Answer 1

NOTE: you should not just strip, but replace with replacement character U+FFFD to avoid unicode attacks, mostly XSS:

http://unicode.org/reports/tr36/#Deletion_of_Noncharacters

preg_replace('/[\x{10000}-\x{10FFFF}]/u', "\xEF\xBF\xBD", $value); 

Answer 2

Since 4-byte UTF-8 sequences always start with the bytes 0xF0-0xF7, the following should work:

$str = preg_replace('/[\xF0-\xF7].../s', '', $str); 

Alternatively, you could use preg_replace in UTF-8 mode but this will probably be slower:

$str = preg_replace('/[\x{10000}-\x{10FFFF}]/u', '', $str); 

This works because 4-byte UTF-8 sequences are used for code points in the supplementary Unicode planes starting from 0x10000.