Allow only English letters and numbers in php

Question

I'm trying to create a filter to allow users to use only English letters (Lowercase & uppercase) and numbers. how can I do that? (ANSI) (not trying to sanitize, only to tell if a string contain non-english letters) That filter should get me a clean database with only english usernames, without multibyte and UTF-8 characters.

And can anyone explain to me why echo strlen(À) outputs '2'? it means two bytes right? wans't UTF-8 chars supposed to contain a single byte?

Thanks

Answer 1

This is how you check whether a string contains only letters from the English alphabet.

if (!preg_match('/[^A-Za-z0-9]/', $string))  {
    //string contains only letters from the English alphabet
}

The other question:

strlen(À)

will not return 2. Maybe you meant

strlen('À')

strlen returns

The length of the string on success, and 0 if the string is empty.

taken from here. So, that character is interpreted as two characters, probably due to your encoding.