PHP Constants
Constants are like variables, except that once they are defined they cannot be changed or undefined.
PHP Constants
A constant is an identifier (name) for a simple value. The value cannot be changed during the script.
A valid constant name starts with a letter or underscore (no $ sign before the constant name).
Note: Unlike variables, constants are automatically global across the entire script.
Create a PHP Constant
To create a constant, use the define() function.
Syntax
define(name, value, case-insensitive);
Parameters:
- name: Specifies the name of the constant
- value: Specifies the value of the constant
- case-insensitive: Specifies whether the constant name should be case-insensitive. Default is false. Note: Defining case-insensitive constants was deprecated in PHP 7.3. PHP 8.0 accepts only false, the value true will produce a warning.
Example
Create a constant with a case-sensitive name:
define("GREETING", "Welcome to W3Schools.com!");
echo GREETING;
Example
Create a constant with a case-insensitive name:
define("GREETING", "Welcome to W3Schools.com!", true);
echo greeting;
PHP const Keyword
You can also create a constant by using the const keyword.
Example
Create a constant with the const keyword:
const MYCAR = "Volvo";
echo MYCAR;
const vs. define()
constare always case-sensitivedefine()has has a case-insensitive option.constcannot be created inside another block scope, like inside a function or inside anifstatement.definecan be created inside another block scope.
PHP Constant Arrays
From PHP7, you can create an Array constant using the define() function.
Example
Create an Array constant:
define("cars", [
"Alfa Romeo",
"BMW",
"Toyota"
]);
echo cars[0];
Constants are Global
Constants are automatically global and can be used across the entire script.
Example
This example uses a constant inside a function, even if it is defined outside the function:
define("GREETING", "Welcome to W3Schools.com!");
function myTest() {
echo GREETING;
}
myTest();
