Question

What is quicker, for camelCase to underscores, preg_replace() or ord()?

My guess is that using ord() will be quicker, since preg_replace() can do much more than needed.

function __autoload($class_name) {
  $name = strtolower(preg_replace('/([a-z])([A-Z])/', '$1_$2', $class_name));
  require_once "some_dir/" . $name . ".php";
}

function __autoload($class_name) {
  $class_name[0] = strtolower($class_name[0]);
    
  $len = strlen($class_name);
  for ($i = 0; $i < $len; ++$i) {
    if (ord($class_name[$i]) > ord('A') && ord($class_name[$i]) < ord('Z')) {
      $class_name[$i] = '_' . strtolower($class_name[$i]);
      ++$len;
      ++$i;
    }
  }
    
  return $class_name;
}

Disclaimer

Code examples are taken from Convert CamelCase to under_score_case in php __autoload().

Edit

After jensgram‘s array-suggestion and finding array_splice(), I have come up with the following.

function __autoload ($string) {
  $string = str_split($string);
  $pos = count($string);

  while (--$pos > 0) {
    $lower = strtolower($string[$pos]);

    if ($string[$pos] === $lower) {
      continue;
    }
    
    unset($string[$pos]);
    array_splice($string, $pos, 0, array('_', $lower));
  }

  $string  =  implode('', $string);
  return $string;
}

When I will test these methods, I will add this one, but feel free to tell me your results anytime.

Answer 1

i think (and i’m pretty much sure) that the preg_replace method will be faster – but if you want to know, why dont you do a little benchmark calling both functions 100000 times and measure the time?