Are php constants global?

PHP Constants

Constant is an identifier (name) of a single value. This value cannot be changed in script.

Valid constant names begin with a character or an underscore (there is no $ sign in front of the constant name). (Recommended learning: PHP video tutorial)

Note: Unlike variables, constants are automatically global throughout the entire script.

Set PHP constants

To set constants, use the define() function - it uses three parameters:

The first parameter defines the constant The name

The second parameter defines the value of the constant

The optional third parameter specifies whether the constant name is case-insensitive. The default is false.

The following example creates a case-sensitive constant with the value "Welcome to php.cn!":

Example

<?php
define("GREETING", "Welcome to php.cn!");
echo GREETING;
?>

Constants are global

Constants are automatically global and can be used throughout the entire script.

The following example uses a constant inside a function even though it is defined outside the function:

Example

<?php
define("GREETING", "Welcome to php.cn!");

function myTest() {
    echo GREETING;
}
 
myTest();
?>

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