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PHP Constants

Constants are variables whose values cannot be changed once defined.

Unlike normal variables, constants:

✅ Cannot be reassigned
✅ Do not use $ sign
✅ Usually store configuration values
✅ Are available globally

Why Use Constants?

Constants are useful for storing:

  • Application Name
  • Version Numbers
  • Database Information
  • API URLs
  • Plugin Information
  • Configuration Values

Creating Constants

PHP provides two ways:

  1. define()
  2. const

Using define()

Syntax:

define("NAME", "VALUE");

Example:

define("SERVER_NAME", "ZyroNetwork");

echo SERVER_NAME;

Output:

ZyroNetwork

Using const

const VERSION = "1.0.0";

echo VERSION;

Output:

1.0.0

Difference Between define() and const

Featuredefine()const
Runtime Definition✅❌
Inside Classes❌✅
Arrays Supported✅✅
Conditional Creation✅❌

Naming Convention

Constants are usually written in:

UPPER_SNAKE_CASE

Example:

const PLUGIN_VERSION = "1.0.0";
const MAX_PLAYERS = 100;

Invalid Example

const version = "1.0";

This works but is not recommended.

Constants Are Immutable

const VERSION = "1.0";

VERSION = "2.0";

Output:

Fatal Error

Constants Are Global

const APP_NAME = "Zyro";

function test() {
    echo APP_NAME;
}

Output:

Zyro

Constant Arrays

const RANKS = [
    "Player",
    "VIP",
    "Admin"
];

print_r(RANKS);

Class Constants

class Server {

    public const VERSION = "1.0";
}

Usage:

echo Server::VERSION;

Final Constants

final class Config {

    public const VERSION = "1.0";
}

PocketMine Example

class Main extends PluginBase {

    public const PREFIX =
        "§6Zyro §8» ";
}

Usage:

$player->sendMessage(
    self::PREFIX . "Welcome!"
);

Magic Constants

PHP provides predefined constants.

LINE

Returns current line number.

echo __LINE__;

Output:

25

FILE

Returns current file path.

echo __FILE__;

DIR

Returns current directory.

echo __DIR__;

FUNCTION

Returns function name.

function test() {
    echo __FUNCTION__;
}

Output:

test

CLASS

Returns class name.

class User {

    public function test() {
        echo __CLASS__;
    }
}

METHOD

Returns full method.

User::test

PHP Built-in Constants

PHP_VERSION
PHP_OS
PHP_INT_MAX
PHP_EOL
DIRECTORY_SEPARATOR

Example:

echo PHP_VERSION;

Real World Example

const API_URL =
"https://api.zyro.network";
const DATABASE_VERSION =
"2.1";
const DISCORD_INVITE =
"https://discord.gg/xxxxx";

Best Practices

✅ Use constants for configuration.

✅ Use uppercase names.

✅ Keep constants meaningful.

Bad Example

const A = 1;
const X = "abc";

Good Example

const SERVER_PORT = 19132;

const DEFAULT_LANGUAGE =
"en_US";

Exercises

Exercise 1​

Create:

const NAME = "Aayan";

Exercise 2​

Create:

const SERVER = "ZyroNetwork";
const VERSION = "1.0.0";

Exercise 3​

Print:

PHP_VERSION
PHP_OS

Quiz

Can constants be changed?​

Answer

No. Constants are immutable.

Which symbol is used?​

Answer

Constants do NOT use $.

Challenge

Create a plugin information file:

const PLUGIN_NAME =
"ZyroCore";

const PLUGIN_VERSION =
"1.0.0";

const API_VERSION =
"5.0.0";

Useful Links

Official Documentation:

https://www.php.net/manual/en/language.constants.php

Magic Constants:

https://www.php.net/manual/en/language.constants.magic.php

Next Chapter

➡ PHP Data Types