检查字符串是否仅由字母数字字符组成的最佳方法是什么？ [重复]

Possible Duplicate:
Php function to determine if a string consist of only alphanumerical characters?

I need to validate the string using PHP and regexpresisons

string can be min. 4 chars, up to 64 and needs to be only aplphanumeric

all I got so far:

/^[A-Za-z0-9]{4,64}$/

Your regex is correct (assuming you only want to match ASCII alphanumerics), so you're probably using it incorrectly. To check whether a string $subject matches this regex, use

if (preg_match('/^[A-Z0-9]{4,64}$/i', $subject)) {
    # Successful match
} else {
    # Match attempt failed
}

Note the /i option to make the regex case-insensitive. If you also want to match other letters/digits, use /^[\p{L}\p{N}]{4,64}$/ as your regex.

if (preg_match('/^[a-z0-9]{4,64}$/i', $subject)) {
    # Successful match
} else {
    # Match attempt failed
}

That's about as minimal as you can make it, though it does incur the regex overhad. Anything would would be more complicated, e.g:

$str = '....';
if (strlen($str) >= 4) && (strlen($str) <= 64) {
   if (function_to_detect_non_alphanum_chars($str)) {
      ... bad string ...
   }
}