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PHP 5 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.
define(name, value, case-insensitive)
  • 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
The example below creates a constant with a case-sensitive name:

define("GREETING", "Welcome to!");
The example below creates a constant with a case-insensitive name:

  1. <?php
  2. define("GREETING", "Welcome to!", true);
  3. echo greeting;
  4. ?>
Constants are Global
Constants are automatically global and can be used across the entire script.
The example below uses a constant inside a function, even if it is defined outside the function:

  1. <?php
  2. define("GREETING", "Welcome to!");
  3. function myTest() {
  4.     echo GREETING;
  5. }
  6. myTest();
  7. ?>


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