define

Definition and usage

define() function defines a constant.

Constants are similar to variables, the difference is:

• The value of a constant cannot be changed after setting
• The constant name does not require a dollar sign ($) that begins with
• Constants can be accessed within any scope
• The value of a constant can only be strings and numbers

Example

Example 1

Define a case-sensitive constant:

 <?php
define ( "GREETING" , "Hello world!" ) ;
echo constant ( "GREETING" ) ;
?>

Try it yourself

Example 2

Define a case-insensitive constant:

 <?php
define ( "GREETING" , "Hello world!" , TRUE ) ;
echo constant ( "greeting" ) ;
?>

Output:

 Hello world!

grammar

 define ( name , value , case_insensitive )

illustrate

After PHP 7.3, it is not recommended to use case-insensitive constant names because this option has been deprecated. When defining constants, a case-sensitive name should always be used.

Additionally, while PHP 7 allows arrays to be used as values ​​for constants, this is not a typical use of constants, as constants are often used to store simple invariant values ​​such as configuration settings or constant expressions.

In PHP 5, the value of a constant must be a scalar type (such as a string, integer, floating point number) or a Boolean value, or NULL.