Safe to use strpos with UTF-8 strings?

Question

I have a bunch of strings with different charsets. The $charset variable contains the charset of the current string.

$content = iconv($charset, \'UT         


        

Answer 1

Functions like strlen() count bytes, not characters.

See the notes in the PHP Manual for details:

Note:

strlen() returns the number of bytes rather than the number of characters in a string.

use the mb_* functions if you're working with UTF-8, unless you have the php.ini setting mbstring.func_overload enabled to overload the standard strops(), strlen(), substr(), etc functions... then strlen() will count characters

Answer 2

That entirely depends on what you want to do. The core strlen and similar functions work on bytes. Every number they accept and return is a byte count or byte offset. The mb_* functions work encoding-aware on characters. All numbers they accept and return are character counts or offsets.

If you have a safe way of getting a byte offset in a string ("safe" meaning the offset is not in the middle of a multi-byte character) and then, for example, crop everything before that offset using substr, that'll work just fine. For instance:

$str     = '漢字';
$offset  = strpos($str, '字');
$cropped = substr($str, $offset);

Works fine.

However, this won't work:

$cropped = substr($str, $offset, 1);

You can't safely cut out a single byte without running the risk of cutting into a multi-byte character.