I am using the stripos function to check if a string is located inside another string, ignoring any cases.
Here is the problem:
stripos("ø", "Ø")
returns false. While
stripos("Ø", "Ø")
returns true.
As you might see, it looks like the function does NOT do a case-insensitive search in this case.
The function has the same problems with characters like Ææ and Åå. These are Danish characters.
Use mb_stripos() instead. It's character set aware and will handle multi-byte character sets. stripos() is a holdover from the good old days when there was only ASCII and all chars were only 1 byte.
You need mb_stripos.
mb_stripos will take care of this.
As the other solutions say, try first with mb_stripos(). But if using this function doesn't help, check the encoding of your php file. Convert it to UTF-8 and save it. That did the trick for me after hours of research.
来源：https://stackoverflow.com/questions/5487917/stripos-returns-false-when-special-characters-is-used