Explanation of constants in php

An identifier of a simple value. Once a constant is defined, it cannot be changed while the script is running. This article mainly shares with you the explanation of constants in php, I hope it can help you.

System constants

• 1) PHP_VERSION php version

• 2) PHP_OS php running system

• 3) PHP_INT_MAX The maximum value of the integer

Custom constant

Definition

define() function definition

define(name, value)

Note:

• ##Do not add $ to the constant name;

• Constant names are preferably in uppercase letters and start with a letter or underscore;

• Constants are case-sensitive by default;

• The value of a constant can be Scalar type, can also be an array (php7)

const Keyword definition

const name = value

Use variables

• 1) Just use the name of the constant directly

• 2)

  Constant(name) Get the value of the constant based on its name

Detect whether the constant

exists

defined(name)

returns

true if it exists, otherwise returns false

Return all defined constants

get_defined_constants()

Return arrays, system and custom constants

Magic variables

Between

Starting and ending with an underscore :

• Get the current line number where the code is located

  _
  LINE _

• Get the complete absolute path and file name of the file

  _ _ FILE_ _
  

• Get Full absolute path to file

  _
  DIR _

• Get the name of the current function

  _
  FUNCTION _

• Get the class name of the current function

  _
  CLASS _

• Get the method name of the current class

  _
  METHOD _

• Get the name of the current TTRAIT

  _
  TRAIT _

• Get the name of the current namespace

  _
  NAMESPACE _

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