PHP autoloader: ignoring non-existing include - php

Question

I have a problem with my autoloader:
public function loadClass($className) {
$file = str_replace(array('_', '\\'), '/', $className) . '.php';
include_once $file;
}
As you can see, it's quite simple. I just deduce the filename of the class and try to include it. I have a problem though; I get an exception when trying to load a non-existing class (because I have an error handler which throws exceptions). This is inconvenient, because it's also fired when you use class_exists() on a non-existing class. You don't want an exception there, just a "false" returned.
I fixed this earlier by putting an # before the include (supressing all errors). The big drawback with this, though, is that any parser/compiler errors (that are fatal) in this include won't show up (not even in the logs), resulting in a hard to find bug.
What would be the best way to solve both problems at once? The easiest way would be to include something like this in the autoloader (pseudocode):
foreach (path in the include_path) {
if (is_readable(the path + the class name)) readable = true;
}
if (!readable) return;
But I worry about the performance there. Would it hurt a lot?
(Solved) Made it like this:
public function loadClass($className) {
$file = str_replace(array('_', '\\'), '/', $className) . '.php';
$paths = explode(PATH_SEPARATOR, get_include_path());
foreach ($paths as $path) {
if (is_readable($path . '/' . $file)) {
include_once $file;
return;
}
}
}

Answer 1

It will only get called once per class, so performance shouldn't be a problem.

Answer 2

public function loadClass($className) {
$file = str_replace(array('_', '\\'), '/', $className) . '.php';
if(is_readable($file))
include_once $file;
}
is_readable won't make a huge performance difference.

Answer 3

class_exists() has a second parameter autoload which, when set to FALSE, won't trigger the autoloader for a nonexistant class.

Answer 4

(Solved) Made it like this:
public function loadClass($className) {
$file = str_replace(array('_', '\\'), '/', $className) . '.php';
$paths = explode(PATH_SEPARATOR, get_include_path());
foreach ($paths as $path) {
if (is_readable($path . '/' . $file)) {
include_once $file;
return;
}
}
}