What is a Constant?
A constant is an identifier for a simple value. Once set, a constant's value cannot change during script execution. Constant names are case-sensitive and, by convention, always written in UPPERCASE. A constant name must begin with a letter or underscore (no $ sign).
How to Define a Constant
Use the define() function. To read the value, just use the constant's name — no $ prefix.
<?php
define("PAGE_TITLE", "PHP Tutorials for Beginners");
define("DESC", "PHP constant tutorial example");
echo PAGE_TITLE; // Output: PHP Tutorials for Beginners
echo DESC; // Output: PHP constant tutorial example
?>
Constants vs Variables
- Constants have no
$sign — variables require it. - Constants are defined with
define()— variables are assigned with=. - Constants are accessible anywhere in the script regardless of scope — variables are subject to scoping rules.
- Once a constant is defined it cannot be redefined or undefined.
Hope this tutorial is useful for you. Keep following PHP Tutorial for Beginners for more help.