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Php constants

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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

The example below creates a constant with a case-sensitive name:

Example

<?php
   define("WELCOME", "Welcome to Breakinterview.com!");
   echo WELCOME;
?>

The example below creates a constant with a case-insensitive name:

Example

<?php 
    define("WELCOME", "Welcome to Breakinterview.com!", true);
    echo welcome;
?>

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:

Example

<?php
    define("WELCOME", "Welcome to Breakinterview.com!");
    function myTest() {  
       echo WELCOME;
    }

    myTest();
?>
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