PHP Constants

In PHP, constants are like variables, but their values cannot be changed or modified during the execution of the script. Once a constant is defined, its value remains the same throughout the entire script’s execution, making them suitable for storing data that should remain constant and unchanged.

To define a constant in PHP, you use the define() function or the const keyword. The basic syntax for defining a constant using the define() function is:

define("CONSTANT_NAME", value, case_insensitive);

• CONSTANT_NAME: The name of the constant. It should follow the same naming rules as variables but is conventionally written in uppercase letters.
• value: The value of the constant, which cannot be changed during the script’s execution.
• case_insensitive: An optional boolean parameter (default is false) that determines whether the constant’s name is case-insensitive. If set to true, the constant’s name can be accessed in a case-insensitive manner.

Example of defining and using a constant using define():

define("SITE_NAME", "My Website");
define("VERSION", 1.2, true); // Case-insensitive constant

echo SITE_NAME; // Output: My Website
echo VERSION;   // Output: 1.2
echo version;   // Output: 1.2 (Case-insensitive access)

Alternatively, you can use the const keyword to define a constant within a class or at the global level:

const PI = 3.14;

echo PI; // Output: 3.14

Unlike regular variables, you don’t use the dollar sign ($) to access constants. You simply use their names to retrieve their values.

Constants are widely used in PHP for defining configuration settings, error codes, database credentials, and other data that should remain constant throughout the execution of the script. They help in improving code readability and maintainability by providing named values instead of using “magic numbers” or hard-coded values directly in the code.