Question

I know of several ways to get a character off a string given the index.

<?php
$string = 'abcd';
echo $string[2];
echo $string{2};
echo substr($string, 2, 1);
?>

I don’t know if there are any more ways, if you know of any please don’t hesitate to add it. The question is, if I were to choose and repeat a method above a couple of million times, possibly using mt_rand to get the index value, which method would be the most efficient in terms of least memory consumption and fastest speed?

Answer 1

To arrive at an answer, you’ll need to setup a benchmark test rig. Compare all methods over several (hundreds of thousands or millions) iterations on an idle box. Try the built-in microtime function to measure the difference between start and finish. That’s your elapsed time.

The test should take you all of 2 minutes to write.

To save you some effort, I wrote a test. My own test shows that the functional solution (substr) is MUCH slower (expected). The idiomatic PHP ({}) solution is as fast as the index method. They are interchangeable. The ([]) is preferred, as this is the direction where PHP is going regarding string offsets.

<?php
$string = 'abcd';
$limit = 1000000;

$r = array(); // results

// PHP idiomatic string index method
$s = microtime(true);
for ($i = 0; $i < $limit; ++$i) {
    $c = $string{2};
}
$r[] = microtime(true) - $s; 
echo "\n";

// PHP functional solution
$s = microtime(true);
for ($i = 0; $i < $limit; ++$i) {
    $c = substr($string, 2, 1); 
}
$r[] = microtime(true) - $s; 
echo "\n";

// index method
$s = microtime(true);
for ($i = 0; $i < $limit; ++$i) {
    $c = $string[2];
}
$r[] = microtime(true) - $s; 
echo "\n";


// RESULTS
foreach ($r as $i => $v) {
    echo "RESULT ($i): $v \n";
}
?>

Results:
RESULT (PHP4 & 5 idiomatic braces syntax): 0.19106006622314
RESULT (string slice function): 0.50699090957642
RESULT (*index syntax, the future as the braces are being deprecated *): 0.19102001190186