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Basics

PHP Constants

Defining PHP Constants

PHP constants use define() or const for immutable values.

What are PHP Constants?

In PHP, constants are simple names or identifiers that hold immutable values. Once defined, they cannot be changed during the execution of the script. Constants are useful for defining values that remain the same throughout your application, such as configuration settings or fixed values.

Defining Constants with define()

The define() function is commonly used to define constants in PHP. It takes two parameters: the name of the constant and its value. Optionally, a third parameter can be used to specify case-insensitivity (default is false).

Defining Constants with const

PHP 5.3 introduced the use of the const keyword to define constants. This method is more restricted compared to define() and can only be used at the top level of a script or inside a class definition.

Differences Between define() and const

  • Scope: const can be used within classes, while define() cannot.
  • Execution: const is evaluated at compile time, whereas define() is executed at runtime.
  • Case Sensitivity: Constants defined with define() can be case-insensitive, but those with const are always case-sensitive.

Best Practices for Using Constants

When using constants, follow these best practices:

  • Use all uppercase letters with underscores for readability (e.g., MAX_LIMIT).
  • Define constants at the beginning of your script to ensure they are available when needed.
  • Use constants for values that do not change during the execution of your script.

Basics

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Magic Constants