If you have certain values that will be the same throughout your application (configuration values for example) you will want to define them up front and then use them in various places, different scopes. To do this with variables, you’d either need to make them global (gross) or create a class or function for accessing them. Then you have the overhead of making a function call every time you need one. This is surely slower than accessing a constant.

Also (and this is just speculation), I’d expect that constants will have the edge when you’re using APC which you should be using at all times.

Anyway, I realize this post is old, but I just ran a test seeing how fast constants and variables are *set*, nevermind retrieved or used, and felt like looking for similar information.
The results: With a million statements each, constants only took 4 seconds, whereas variable took 44 MINUTES to be set…
In other words, if you aren’t going to change your values, you’re saving a lot of time setting constants over variables.

You know, I believe that it all depends on the hardware, probably variables are more subject to RAM, while contants to hard drive and cpu.

A

<?php
$i = 0;
while(true){
<<>>
$i ++;
echo $i, “_”;
}

where <<>> is the one of the code below, which followed by the highest value of $i I got,

define(“var”.$i, “X”); // highest value of $i = 2091796
${“var”.$i} = “X”; // highest value of $i = 217845
$var[] = “X”; // highest value of $i = 245070
$var[][] = “X”; // highest value of $i = 84420

While you showed that constants are the slowest, they are, by far, the least resource intensive,

suprising is that arrays are also less resource intensive then normal variables, even though this effect weakens with multi-demensional arrays

anyhow, great job on this and thnx

so? should we use variables?