UTF-8 & IsAlpha() in PHP

Question

I'm working on a application which supports several languages and has a functionality in place which tries to use the language requested by the browser and also allows manual override of this function. This part works fine and picks the correct templates, labels, etc.

User have to enter sometimes text on their own and that's where I run into issues because the application has to accept even "complicated" languages like Chinese and Russian. So far I've taken care of the things mentioned in other posting, i.e.:

• calling mb_internal_encoding( 'UTF-8' )
• setting the right encoding when rendering the webpages with meta http-equiv=Content-Type content=text/html;charset=UTF-8 (format adapted due to stackoverflow limitations)
• even the content arrives correctly, because mb_detect_encoding() == UTF-8
• tried to set setLocale(LC_CTYPE, "UTF-8"), which doesn't seem to work because it requires the selection of one language, which I can't specify because I have to support several. And it still fails if I force it manually for testing purposes, i.e. with; setLocale(LC_CTYPE,"zh__CN.utf8") - ctype_alpha() would still fail for Chinese text

It seems that even explicit language selection doesn't make ctype_alpha() useful.

Hence the question is: how should I check for alphabetic characters in all languages?

The only idea I had at the moment is to check manually with arrays of "valid" characters - but this seems ugly especially for Chinese.

How would you solve this issue?

Answer 1

If you'd like to check only for valid unicode letters regardless of the used language I'd propose to use a regular expression (if your pcre-regex extension is built with unicode support):

// adjust pattern to your needs
// $input needs to be UTF-8 encoded
if (preg_match('/^\p{L}+$/u', $input)) {
    // OK
} else {
    // not OK
}

\p{L} checks for unicode characters with the L(etter) property which includes the properties Ll (lower case letter), Lm (modifier letter), Lo (other letter), Lt (title case letter) and Lu (upper case letter) - from: Regular Expression Details).