• PHP constants are identifier or name that can’t be changed during the execution of the script except for magic constants, which are not really constants.
  • Constants can never be undefined or changed, they are similar to the variable except once defined.
  • PHP constants follow the same PHP variable rules and it remains constant across the entire program.
  • Conventionally, in uppercase letters PHP constants should be defined and it can be started with an underscore or letter only.
  • PHP constants consists of two types, they are:
    • Using define () function
    • Using const keyword

Using define () function

  • In PHP use the define () function to create a constant and it defines constant at run time.
  • In this function name specifies the constant name, value specifies the constant value and case-insensitive specifies whether a constant is case-insensitive.
  • By default, if value is false it means it is case sensitive.

Sample Code

<?php    
define("MESSAGE","Welcome to Wikitechy",true);//not case sensitive
echo MESSAGE, "</br>";
echo message;
?>

Output

Using const Keyword

  • PHP introduces a const keyword to create a constant and it defines constants at compile time.
  • It constructs a language, not a function.
  • The constant defined using const keyword are case-sensitive.

Sample Code

<?php      
define("MSG", "Wikitechy");
echo MSG, "</br>";
echo constant("MSG");
//both are similar
?>

Output

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