in_array vs strpos for performance in php

Question

I am logging in users via windows authentication and then storing that user's rights in a session variable. I use a delimited method of rights storage in a database i.e:

$rights //retrieved from database 
= 'read,edit,delete,admin'

so my question is should I;

//generate variable
$_SESSION['userrights'] = $rights ($rights is retrieved from database)

//use strpos to find if right is allowed
if (strpos($_SESSION['userrights'],"admin") !== false) { // do the function }

OR

//make array of rights
$_SESSION['userrights'] = explode(',',$rights)

//use in_array to find if right is allowed
if (in_array("admin",$_SESSION['userrights'])) { // do the function }

Bit of a OCD question as I presume the difference will be pretty much negligible for what I am doing but which would be the faster (use less resources) method?

Any answers appreciated except ones that insult my method of rights storage!

Answer 1

As I often work with large datasets, I'd go with isset or !empty on an associative array and check for the key, like @Barmar suggests. Here is a quick 1M benchmark on an Intel® Core™ i3-540 (3.06 GHz)

$test = array("read", "edit", "delete", "admin");

echo "<pre>";

// --- strpos($rights,$test[$i%4]) ---

$rights = 'read,edit,delete,admin';
$mctime = microtime(true);
for($i=0; $i<=1000000; $i++) { if (strpos($rights,$test[$i%4]) !== false) { }}
echo '  strpos(... '.round(microtime(true)-$mctime,3)."s\n";

// --- in_array($test[$i%4],$rights) ---

$rights = array("read", "edit", "delete", "admin");
$mctime = microtime(true);
for($i=0; $i<=1000000; $i++) { if (in_array($test[$i%4],$rights)) { }}
echo 'in_array(... '.round(microtime(true)-$mctime,3)."s\n";

// --- !empty($rights[$test[$i%4]]) ---

$rights = array('read' => 1, 'edit' => 1, 'delete' => 1, 'admin' => 1);
$mctime = microtime(true);
for($i=0; $i<=1000000; $i++) { if (!empty($rights[$test[$i%4]])) { }}
echo '  !empty(... '.round(microtime(true)-$mctime,3)."s\n";

// --- isset($rights[$test[$i%4]]) ---

$rights = array('read' => 1, 'edit' => 1, 'delete' => 1, 'admin' => 1);
$mctime = microtime(true);
for($i=0; $i<=1000000; $i++) { if (isset($rights[$test[$i%4]])) { }}
echo '   isset(... '.round(microtime(true)-$mctime,3)."s\n\n";

echo "</pre>";

The winner is isset:

  strpos(... 0.393s
in_array(... 0.519s
  !empty(... 0.232s
   isset(... 0.209s

Answer 2

strpos is the fastest way to search a text needle, per the php.net documentation for strstr():

If you only want to determine if a particular needle occurs within haystack, use the faster and less memory intensive function strpos() instead.¹

Answer 3

A benchmark that proofs that strpos is not the fastest method, but faster than in_array:

<?php

echo phpversion() . PHP_EOL;

// build random array
$array = array_fill(0, 10000, 16);
$array = array_map('openssl_random_pseudo_bytes', $array);
$array = array_map('bin2hex', $array);
$array_flipped = array_flip($array);
$string = implode($array);
$random_keys = array_rand($array_flipped, 10);

$loops = 10000;

$start = microtime(true);
for ($i = 0; $i < $loops; $i++) {
    strpos($string, $random_keys[ rand(0, 9) ]);
}
echo __LINE__ . ': ' . round(microtime(true) - $start, 5) . PHP_EOL;

$start = microtime(true);
for ($i = 0; $i < $loops; $i++) {
    in_array($random_keys[ rand(0, 9) ], $array);
}
echo __LINE__ . ': ' . round(microtime(true) - $start, 5) . PHP_EOL;

$start = microtime(true);
for ($i = 0; $i < $loops; $i++) {
    isset($array_flipped[ $random_keys[ rand(0, 9) ] ]);
}
echo __LINE__ . ': ' . round(microtime(true) - $start, 5) . PHP_EOL;

$start = microtime(true);
for ($i = 0; $i < $loops; $i++) {
    $array_flipped = array_flip($array);
    isset($array_flipped[ $random_keys[ rand(0, 9) ] ]);
}
echo __LINE__ . ': ' . round(microtime(true) - $start, 5) . PHP_EOL;

?>

Result:

5.6.31
19: 1.11484
25: 1.3109
31: 0.00237
38: 13.64204

As you can see it is important not to flip an array on-the-fly to benefit from isset.

Answer 4

Have you considered the possibility of doing a query on the database if $_SESSION['userrights'] exists in the database? You're already doing a query to get the list of rights in your example, why not do a query for a specific $_SESSION['userrights'] and check if there are any rows returned?