PHP's str_replace() was intended only for ANSI strings and as such can mangle UTF-8 strings. However, given that it's binary-safe would it work properly if it was only given valid UTF-8 strings as arguments?
Edit: I'm not looking for a replacement function, I would just like to know if this hypothesis is correct.
Yes. UTF-8 is deliberately designed to allow this and other similar non-Unicode-aware processing.
In UTF-8, any non-ASCII byte sequence representing a valid character always begins with a byte in the range \xC0-\xFF. This byte may not appear anywhere else in the sequence, so you can't make a valid UTF-8 sequence that matches part of a character.
This is not the case for older multibyte encodings, where different parts of a byte sequence are indistinguishable. This caused a lot of problems, for example trying to replace an ASCII backslash in a Shift-JIS string (where byte \x5C might be the second byte of a character sequence representing something else).
It's correct because UTF-8 multibyte characters are exclusively non-ASCII (128+ byte value) characters beginning with a byte that defines how many bytes follow, so you can't accidentally end up matching a part of one UTF-8 multibyte character with another.
To visualise (abstractly):
a for an ASCII character2x for a 2-byte character3xx for a 3-byte character4xxx for a 4-byte characterIf you're matching, say, a2x3xx (a bytes in ASCII range), since a < x, and 2x cannot be a subset of 3xx or 4xxx, et cetera, you can be safe that your UTF-8 will match correctly, given the prerequisite that all strings are definitely valid UTF-8.
Edit: See bobince's answer for a less abstract explanation.
Well, I do have a counter example: I have a UTF8 encoded settings ".ini' file specifying appliation settings like email sender name. it says something like:
email_from = Märta
and I read it from there to variable $sender. Now that I replace the message body (UTF8 again)
regards {sender}
$message = str_replace("{sender}",$sender_name,$message);
The email is absolutely correct in every respect but the sender is totally broken. There are other cases (like explode() ) when something goes wrong with a UTF string. It is healthy before the conversion but not after it. Sorry to say there seems to be no way of correcting this behaviour.
Edit: Actually, explode() is involved in parsing the .ini file so the problem may well lie in that very function so the str_replace() may well be innocent.
No you cannot.
From practice I am telling you if you have some multibyte symbols like ◊ etc, and others are non-multibyte it wont work correctly, because there are symbols that take 2-4 to place them,
str_replace takes fixed bytes, and replaces... In result we have something that isn't any symbols trash etc.
Yes, I think this is correct, at least I couldn't find any counter-example.
