PHP: Find the second (or third) occurrence of a substr in a string

I needed to find the second occurrence of a substring inside of a larger string. PHP has strpos() which gets you the first occurrence, but nothing beyond that. I wrote a wrapper function around strpos() to let you specify the number you want to find. Returns false if nothing is found.

function strpos_num(string $haystack, string $needle, int $num) {
    $offset = 0;
    $length = strlen($needle);
    $pos    = null;

    for ($i = 0; $i < $num; $i++) {
        $pos = strpos($haystack, $needle, $offset);

        // Short circuit continued lookups if we don't find anything
        if ($pos === false) { return false; }

        $offset = $pos + $length;

    return $pos;

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