A constant is an identifier whose value cannot be changed once it is declared in the program.
Rules for declaring a constant :
- Constants are case-sensitive and conventionally are always UPPERCASE.
- A valid constant name always starts with a letter or an underscore(_) and is followed by any number of letters, numbers and underscores.
- define() function is used to define a constant.
- Constant can be accessed by writing its name or by calling constant() function if you want to obtain a constant value dynamically.
- PHP constants are global and can be used throughout the program.
Syntax to declare a constant :
declare(name, value, case-insensitive);
name : name of the constant.
value : value of the constant.
case-insensitive : specifies whether the constant name would be case sensitive or not. By default its value is false.
<?php define(“MESSAGE”, “WELCOME TO OUR SITE”); echo MESSAGE; echo constant(‘MESSAGE’); ?>