PHP difference between Single-byte strings and Multi-byte strings

Question

For dummies, in PHP what is the difference between single-byte strings and multi-byte strings and in which situations should we consider one or another?

For single-byte strings (e.g. US-ASCII, ISO 8859 family, etc.) use substr and for multi-byte strings (e.g. UTF-8, UTF-16, etc.) use mb_substr:
// singlebyte strings
$result = substr($myStr, 0, 5);
// multibyte strings
$result = mb_substr($myStr, 0, 5);

For instance, if I plan to develop something to be used in china, do I need to adopt any special measures because of their special characters ? Isnt' Utf-8 encoding good enough?

PHP doesnt understand UTF-8, you need to tell it that your string is UTF-8 (as chinese characters are), then use 'mb_x' functions to work on them. Notice that 'mb_x' funcs are working on x-bytes per 1 character, while non 'mb_x' are working on 1-byte per character. — user1299518
– user1299518, Commented May 23, 2014 at 5:54
You can always use mb_ functions, regardless the characterset, and be on the safe site — Maxim Krizhanovsky
– Maxim Krizhanovsky, Commented May 23, 2014 at 6:17

ZhukV · Accepted Answer · 2014-05-23 05:59:15Z

3

The function strlen (Single bytes) returned full count bytes, and function mb_strlen returned count characters!

The char can be have a more then 1 byte (UTF-8 for example).

For you example:

$myStr = '៘៥឴ឨឆ';
$result = substr($myStr, 0, 5);
$result = mb_substr($myStr, 0, 5, mb_detect_encoding($myStr));

Function substr in this example return invalid value, because chars have more the one byte, but function mb_substr returned correct data.

answered May 23, 2014 at 5:59

ZhukV

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