Using define() to Create Constants in PHP

In PHP, you can use the define() function to define constants.

Syntax

define(name, value, case-insensitive);

Parameters:

name: the name of the constant.

value: the constant's value (any data type).

case-insensitive: optional boolean indicating whether the constant name is case‑insensitive; defaults to false.

Example

define('MY_CONSTANT', 'Hello World');
echo MY_CONSTANT; // outputs: Hello World

Notes

Constant names must start with a letter or underscore, followed by letters, numbers, or underscores.

Constant names are case‑sensitive unless case-insensitive is set to true.

Once defined, a constant's value cannot be changed.

Constant names are usually written in uppercase to distinguish them from variables.

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