How to declare a Constant Variable in PHP?
Creating constants in PHP allows us to define values that remain unchanged throughout the execution of a script. This is particularly useful for storing configuration settings, such as database credentials or API keys, as well as for defining global variables that should not be altered during runtime.
Note: In PHP, the two methods mentioned earlier (define( )
and const
) are the primary ways to create constants.
Using the define() function:
It allows defining constants with a function call, accepting two arguments for the constant name and value. Global scope.
define("PI", 3.14);
echo PI;
// Outputs: 3.14
Using the const keyword
It declares class constants or global constants within a file, offering a more concise syntax and being restricted to compile-time constant expressions.
const CONSTANT_NAME = "constant_value";
Features
- Immutable Values: Once defined, constants cannot be changed or redefined elsewhere in the script.
- Accessing Constants: Constants are accessed without the leading
$
symbol. Example:echo CONSTANT_NAME;
- Convention: By convention, constant names are usually uppercase.
- Usage: Constants are commonly used for storing configuration values, such as database credentials or API keys, that remain constant during script execution.