PHP const Keyword

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May 2, 2025 - 10:47
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In PHP, the const keyword is used to define constants. Constants are similar to variables, but once they are defined, they cannot be changed or undefined.

Syntax

const CONSTANT_NAME = value;

  • Constants are automatically global across the entire script.

  • Constant names must follow the same naming rules as variables (start with a letter or underscore).

  • Constants are typically written in uppercase by convention.

Example

class MyClass { const VERSION = "1.0"; public function showVersion() { echo self::VERSION; } } $obj = new MyClass(); $obj->showVersion(); // Outputs: 1.0

Key Points

  • const is used for defining class constants or global constants.

  • Constants defined with const are resolved at compile time.

  • For defining constants outside of a class, you can also use the define() function (more dynamic).

define("SITE_NAME", "My Website"); // alternative way (older style)