PHP String concatenation - "$a $b" vs $a . " " . $b - performance

Question

Is there a speed difference between, say:

$newstring = "$a and $b went out to see $c";

and

$newstring = $a . " and " . $b . " went out to see " . $c;

and if so, why ?

Answer 1

Depending on the PHP version, it varies by how much the second is faster if you write it like: $newstring = $a . ' and ' . $b . ' went out to see ' . $c;

PHP is very inconsistent from version to version and build to build when it comes to performance, you have to test it for yourself. What nees to be said is that it also depends on the type of $a, $b and $c, as you can see below.

When you use ", PHP parses the string to see if there are any variable/placeholders used inside of it, but if you use only ' PHP treats it as a simple string without any further processing. So generally ' should be faster. At least in theory. In practice you must test.

---

Results(in seconds):

a, b, c are integers:
all inside "     : 1.2370789051056
split up using " : 1.2362520694733
split up using ' : 1.2344131469727

a, b, c are strings:
all inside "     : 0.67671513557434
split up using " : 0.7719099521637
split up using ' : 0.78600907325745  <--- this is always the slowest in the group. PHP, 'nough said

Using this code with Zend Server CE PHP 5.3:

<?php

echo 'a, b, c are integers:<br />';
$a = $b = $c = 123;

$t = xdebug_time_index();
for($i = 1000000; $i > 0; $i--)
    $newstring = "$a and $b went out to see $c";
$t = xdebug_time_index() - $t;
echo 'all inside " : ', $t, '<br />';

$t = xdebug_time_index();
for($i = 1000000; $i > 0; $i--)
    $newstring = $a . " and " . $b . " went out to see " . $c;
$t = xdebug_time_index() - $t;
echo 'split up using " : ', $t, '<br />';

$t = xdebug_time_index();
for($i = 1000000; $i > 0; $i--)
    $newstring = $a . ' and ' . $b . ' went out to see ' . $c;
$t = xdebug_time_index() - $t;
echo 'split up using \' : ', $t, '<br /><br />a, b, c are strings:<br />';

$a = $b = $c = '123';

$t = xdebug_time_index();
for($i = 1000000; $i > 0; $i--)
    $newstring = "$a and $b went out to see $c";
$t = xdebug_time_index() - $t;
echo 'all inside " : ', $t, '<br />';

$t = xdebug_time_index();
for($i = 1000000; $i > 0; $i--)
    $newstring = $a . " and " . $b . " went out to see " . $c;
$t = xdebug_time_index() - $t;
echo 'split up using " : ', $t, '<br />';

$t = xdebug_time_index();
for($i = 1000000; $i > 0; $i--)
    $newstring = $a . ' and ' . $b . ' went out to see ' . $c;
$t = xdebug_time_index() - $t;
echo 'split up using \' : ', $t, '<br />';

?>

Answer 2

There likely will be a speed difference, since it's two different syntaxes. What you need to ask is if the difference is important. In this case, no, I don't think you need to be worried. The difference would be too negligible.

I would recommend you doing whatever makes most sense to you visually. "$a and $b went out to see $c" can be a bit confusing when looking at it. If you wanted to go that route, I'd suggest curly-braces around your variables: "{$a} and {$b} went out to see {$c}".