strlen() and UTF-8 encoding

Assuming UTF-8 encoding, and strlen() in PHP, is it possible that this string has a length of 4?

I'm only interested to know about strlen(), not other functions

This is the string:

$1�2

I have tested it on my own computer, and I have verified UTF-8 encoding, and the answer I get is 6.

I don't see anything in the manual for strlen or anything I've read on UTF-8 that would explain why some of the characters above would count for less than one.

PS: This question and answer (4) comes from a mock test for ZCE I bought on Ebay.

Solution 1:

how about using mb_strlen() ?

http://lt.php.net/manual/en/function.mb-strlen.php

But if you need to use strlen, its possible to configure your webserver by setting mbstring.func_overload directive to 2, so it will automatically replace using of strlen to mb_strlen in your scripts.

Solution 2:

The string you posted is six character long: $1�2 (dollar sign, digit one, lowercase i with diaeresis, upside-down question mark, one half fraction, digit two)

If strlen() was called with a UTF-8 representation of that string, you would get a result of nine (probably, though there are multiple representations with different lengths).

However, if we were to store that string as ISO 8859-1 or CP1252 we would have a six byte long sequence that would be legal as UTF-8. Reinterpreting those 6 bytes as UTF-8 would then result in 4 characters: $1�2 (dollar sign, digit one, Unicode Replacement Character, digit 2). That is, the UTF-8 encoding of the single character '�' is identical to the ISO-8859-1 encoding of the three characters "�".

The replacement character often gets inserted when a UTF-8 decoder reads data that's not valid UTF-8 data.

It appears that the original string was processed through multiple layers of misinterpretation; by the use of a UTF-8 decoder on non-UTF-8 data (producing $1�2), and then by whatever you used to analyze that data (producing $1�2).