Constant in PHP-

  • A constant is an identifier for holding a value that can not be changed during program or script execution.
  • The constant value cannot change during the execution of the program or script  (except for magic constants, which aren't actually constants).
  • In PHP a constant is case-sensitive by default.
  • Constant identifiers name should  always uppercase by convention but not mandatory.
  • The constant name declaration follow the same rules as any label in PHP. A valid constant name begin with a letter or underscore, followed by any number of letters, numbers, or underscores.

Creating a PHP Constant-

To create a constant, use the define() function.


define(name, value, case-insensitive)
name: Refers the name of the constant
value: Refers the value of the constant
case-insensitive: Refers whether the constant name should be case-insensitive. Default is false

The following example demonstrate a constant with a case-sensitive name -


// Valid constant names

define("PI", "3.14");

define("MESSAGE", "Data saved successfully.");

define("ERROR_MESSAGE", "Error! data could not be saved.");



Note- The scope of a constant is global. You can access constants anywhere in your script without regard to scope.

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