PHP Constants

A constant is a value to which we assign a name, and this value will not change. For example, consider a value of a tax such as VAT.

We can see Constants, that are often used in WordPress configuration, as an example. Here’s how to define a constant.

By convention, the name of the constant is recommended to be in uppercase. A constant distinguishes between uppercase and lowercase letters.

The name of a constant must start with a letter or underscore. This one is defined using the define function

<?php
//impuesto es distinto de impuesto escribir el nombre de una constante //en minusculas no es recomendado
define("IMPUESTO",2.5);
define("impuesto","hola");
?>

Well, we define a constant, but how do we use it?

<?php
   define("IMPUESTO",2.5);
   echo constant("IMPUESTO");
   echo IMPUESTO; //ambos impresiones darán lo mismo
?>

Constants can also be defined using the word “const” before the constant name. With “const”, you can define a constant inside or outside a class, but with “define” it can only be defined outside of classes in the global scope.

<?php
   const IMPUESTO = 22;
   echo IMPUESTO; //ambos impresiones darán lo mismo
?>

Predefined constants

PHP provides numerous predefined constants to any executing script. Many of these constants, however, are created by different extensions and will only be present if these extensions are available, either through dynamic loading or because they have been compiled. php.net

Predefined constant are also called “magic constants”

Magic Constants table

References: php.net

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