Description:
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If code sets incorrect character set (utf-8 instead of big5 in test case), mb_strpos() can incorrectly report needle position in some cases. It looks like $offset is calculated one way and results are calculated in some other way. See test code. mb_substr($str,$pos1,1,'utf-8') can be used to see character that is in reported needle position.

I understand that $str is not in UTF-8 charset, but position reported by mb_strpos() violates very basic strpos function behavior. Search is started after $offset position and result position is counted from string start. Result should not be lower than $offset or it should be boolean false.

php5.3-201008291230
compiled with /configure --prefix=/somepath --enable-cli --disable-all --enable-mbstring

Also tested PHP 5.2.0 (debian etch), 5.3.2-2 (debian squeeze) and 5.2.13 (standard PHP package). 5.2.13 and 5.3.2 results are the same. 5.2.0 results are a little bit different, but I was able to reproduce position calculation problem with more complex code.


Test script:
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$str = "\xb7\x51 &\xb4\xa6\xb6\x7d";
$pos1 = mb_strpos($str,'&',0,'utf-8');
var_dump($pos1);
$pos2 = mb_strpos($str,'&',$pos1 + 1,'utf-8');
var_dump($pos2);

Expected result:
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second var_dump() result should be higher than first one or should be boolean false.

result should not be lower than offset.


Actual result:
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int(2)
int(2)