Question

1] Which of the functions is faster?
2] what are the differences?

Differences

1] readdir returns the name of the next entry in the directory. Scandir returns an array of files and directories from the directory.

2] readdir has to have a resource handle open until all the entries are read. scandir, perhaps creates an array of all the entries and closes the resouce handle?

Answer 1

Just getting the results (without doing anything), readdir is a minimum faster:

<?php

$count = 10000;

$dir = '/home/brati';

$startScan = microtime(true);
for ($i=0;$i<$count;$i++) {
    $array = scandir($dir);
}
$endScan = microtime(true);


$startRead = microtime(true);
for ($i=0;$i<$count;$i++) {
    $handle = opendir($dir);
    while (false !== ($entry = readdir($handle))) {
        // We do not know what to do
    }
}
$endRead = microtime(true);

echo "scandir: " . ($endScan-$startScan) . "\n";
echo "readdir: " . ($endRead-$startRead) . "\n";

Gives:

== RUN 1 ==
scandir: 5.3707950115204
readdir: 5.006147146225

== RUN 2 ==
scandir: 5.4619920253754
readdir: 4.9940950870514

== RUN 3 ==
scandir: 5.5265231132507
readdir: 5.1714680194855

Then of course it depends on what you intend to do. If you have to write another loop with scandir(), it will be slower.