How to define constants in PHP?

Constants are more likely to be used as identifiers since their values CAN NOT change. The magic constants are a bit different in that sense.

Constant identifiers are case-sensitive but they are always defined in uppercase.

Before PHP 8, that wasn’t the case. If you had used define() function to define constants, they might not be case-sensitive!

The scope of a constant is global.

Rules to define a constant

Constant names are like any other variable names.

A valid constant name would start with a letter or underscore and you can add as many numbers, letters, underscores you want.

This is how you can define constants:

define("SITE", "yogeshchauhan.com");
define("BLOG", "yogeshchauhan.com");

You CAN NOT start a constant name with a number:

//NOT VALID
define("1SITE", "yogeshchauhan.com");
define("2BLOG", "yogeshchauhan.com");

This is valid but not recommended:

//NOT VALID
define("__SITE__", "yogeshchauhan.com");
define("__BLOG__", "yogeshchauhan.com");

PHP has magic constants and if in future they use the same name to add magic constant then that might break your code.

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