PHP Constants

A single value identifier is referred to as a constant (name). It cannot change the value while the script is running.

A valid constant name begins with a letter or underscore (there is no $ sign preceding the constant name).

Note :- Contrary to variables, constants automatically reach the whole script globally.

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Create a PHP Constant

Use the define() method to build a constant.

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.

Exampe 1 :- Create a constant with a case-sensitive name.

define("Message", "Welcome to!");
echo Message;

Output :-

Welcome to!

Example 2 :- Create a constant with a case-insensitive name:

define("MESSAGE", "Welcome to!", true);
echo message;

Output :-

Welcome to!

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Constants are Global

Constants are globally automated and can be used throughout the script.

Example :- This example utilizes a function constantly, even though it is specified outside of the function :

define("GREETING", "Welcome to!");

function myTest() {
  echo GREETING;

Output :-

Welcome to!

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PHP Constant Arrays

The define() method in PHP7 allows you to build an Array constant.

Example :- Create an Array constant:

define("cars", [
  "Alfa Romeo",
echo cars[0];

Output :-

Alfa Romeo

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