PHP Constants
A PHP constant is a name or an identifier for a simple value. A constant value cannot change during the execution of the script.
Rules About Constant
- By default, a constant is case-sensitive.
- By convention, constant identifiers are always uppercase.
- A constant name starts with a letter or underscore, followed by any number of letters, numbers, or underscores.
- If you have defined a constant, it can never be changed or undefined.
define() Function to Create Constant In PHP
To define a constant you have to use define() function and to retrieve the value of a constant, you have to simply specifying its name. Unlike with variables, you do not need to have a constant with a $.
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
<?php
define("value", 100);//with case-sensitive name
echo value;
?>Run : http://ideone.com/loOavd
Tutorials Class - Output Window
100
<?php
define("VALUE", 100,true);//with case-insensitive name
echo value;
?>Run : http://ideone.com/b35n1R
constant() Function to read Constant Value
You can also use the function constant() to read a constant’s value if you wish to obtain the constant’s name dynamically.
<?php
define("value", 50);//with case-sensitive name
echo value;
echo "<br>";
echo constant("value");
?>Run : http://ideone.com/fpOLzH
Tutorials Class - Output Window
50
50
Constants are Global
Constants are automatically global and can be used across the entire script.
<?php
define("Value", 100);
function myGlobal() {
echo Value;
}
myGlobal();
?>Run : http://ideone.com/wIumDX
Tutorials Class - Output Window
100
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