Function to return only alpha-numeric characters from string?

I'm looking for a php function that will take an input string and return a sanitized version of it开发者_开发问答 by stripping away all special characters leaving only alpha-numeric.

I need a second function that does the same but only returns alphabetic characters A-Z.

Any help much appreciated.

Warning: Note that English is not restricted to just A-Z.

Try this to remove everything except a-z, A-Z and 0-9:

$result = preg_replace("/[^a-zA-Z0-9]+/", "", $s);

If your definition of alphanumeric includes letters in foreign languages and obsolete scripts then you will need to use the Unicode character classes.

Try this to leave only A-Z:

$result = preg_replace("/[^A-Z]+/", "", $s);

The reason for the warning is that words like résumé contains the letter é that won't be matched by this. If you want to match a specific list of letters adjust the regular expression to include those letters. If you want to match all letters, use the appropriate character classes as mentioned in the comments.

try this to keep accentuated characters:

$result = preg_replace("/[^A-zÀ-ú0-9]+/", "", $s);

Rather than preg_replace, you could always use PHP's filter functions using the filter_var() function with FILTER_SANITIZE_STRING.