What is PHP constant() Function?
If you want to get a constant name, use PHP constant() function.
Syntax:
constant(CONSTANT_NAME)
Parameters:
The function has one parameter which is required-
CONSTANT_NAME (Required): Name of the constant.
Return Values:
The function returns-
- Value of the constant – if the constant has been defined.
- Fatal Error (Undefined error) – if the constant has not been defined.
Examples:
Example 1:
<?php
define("SITENAME", "Schools of Web");
echo constant("SITENAME");
?>
Output:
Schools of Web
Explanation:
The function constant() displays the constant name that was defined previously.
Example 2:
<?php
echo constant("SITEURL");
?>
Output:
Fatal error: Uncaught Error: Undefined constant “SITEURL” in D:\xampp\htdocs\php\constant.php:2 Stack trace: #0 D:\xampp\htdocs\php\constant.php(2): constant(‘SITEURL’) #1 {main} thrown in D:\xampp\htdocs\php\constant.php on line 2
Explanation:
The constant() function is trying to display such a constant that has not been defined, so, PHP throws an error.
Example 3:
<?php
$content = "CONTENT";
define("SITE_" . $content, "Web Development");
echo constant("SITE_" . $content);
?>
Output:
Web Development
Practical Usages of constant() Function:
- To print a constant.
- To retrieve a constant value but you don’t know its name (it may be stored in a variable or it is returned by a function). Check example 3.
PHP Version Support:
PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8
Summary: PHP constant() Function
constant() is a straightforward and short built-in miscellaneous type function in PHP which help provide constant name of a defined constant.