Determine if UTF-8 text is all ASCII? [duplicate]

Question

What's the fastest way, in PHP, to determine if some given UTF-8 text is purely ASCII or not?

Burletta

Answer 1

A possibly faster function would be to use a negative character class (since the regex can just stop when it hits the first character, and there's no need to internally capture anything):

function isAscii($str) {
    return 0 == preg_match('/[^\x00-\x7F]/', $str);
}

Without regex (based on my comment) {

function isAscii($str) {
    $len = strlen($str) {
    for ($i = 0; $i < $len; $i++) {
        if (ord($str[$i]) > 127) return false;
    }
    return true;
}

But I'd have to ask, why are you so concerned about faster? Use the more readable and easier to understand version, and only worry about optimizing it when you know it's a problem...

Edit:

Another option is mb_check_encoding:

function isAscii($str) {
    return mb_check_encoding($str, 'ASCII');
}

Palaeontology

this will be run over a lot of text frequently, and I think both of those are pretty readable, so faster is definitely better here. – Burletta

@philfreo: Updated an answer... But the best way for you to tell what's fastest is to actually benchmark the options using your conditions... – Palaeontology

but apparently php's ord function has issues with utf-8 – Syntactics

No, ord() is always a single-byte "value of this byte" function. – Palaeontology

Note that mb_check_encoding is extremely slow, the preg_match approach will win, always. – Sapless

BENCHMARK (on small ASCII string): reg exp is the fastest approach. for loop and mb_check_encoding are ~7x slower. – Khelat

Answer 2

Check if any byte is greater than 0x7f, or any character is above U+007F.

Guayaquil

Quite simple $isNotAscii = false; for ($i=0,$len=strlen($string);$i<$len;$i++) { if (ord($string[$i]) > 127) { $isNotAscii = true; break; } }. It iterates over each character of the string looking for a character > 127... – Palaeontology

I believe preg_match will be faster in this case... did not benchmark but for strings pattern matching, it almost always is – Domineer

Answer 3

function isAscii($str) {
    return preg_match('/^([\x00-\x7F])*$/', $str);
}

// doesn't accept ASCII control characters
function isAsciiText($str) {
    return preg_match('/^([\x09\x0A\x0D\x20-\x7E])*$/', $str);
}

Burletta

this will fail on some valid ASCII control characters – Doublebank