PHP Constants Types

In PHP, there are two types of constants:

1. Defined Constants: These are constants that are defined using the define() function. Once defined, these constants cannot be changed or undefined during the execution of the script. The syntax for defining a constant is: sql Copy code define(name, value, case-insensitive) Where name is the name of the constant, value is the value assigned to the constant, and case-insensitive is an optional parameter that indicates whether the constant should be case-insensitive or not.
2. Magic Constants: These are predefined constants that are available in PHP at all times. These constants are called “magic” because they are automatically set by PHP based on the context in which they are used. For example, the __LINE__ constant represents the current line number of the script, and the __FILE__ constant represents the full path and filename of the script. Some common magic constants include:
   • __LINE__
   • __FILE__
   • __DIR__
   • __FUNCTION__
   • __CLASS__
   • __TRAIT__
   • __METHOD__
   • __NAMESPACE__
   These constants can be used in any part of the script and will always return the appropriate value based on the context in which they are used.