Constants are similar to the variable except once they defined, they can never be undefined or changed. A constant value cannot change during the execution of the script. Once a constant is defined, it cannot be undefined or redefined.
Generally, PHP constants are defined in uppercase letters.
PHP constants follow the same PHP variable naming rules. A valid constant name starts with a letter or underscore (no $ sign before the constant name). Constants are case-sensitive.
Unlike variables, constants are automatically global across the entire script.
The define() function in PHP is used to create a constant.
PHP constant: define()
Use the define() function to create a constant. It defines constant at run time.
define(ConstantName, value, case-insensitive)
- ConstantName: It specifies the constant name.
- value: The value to be stored in the constant.
- case-insensitive: Specifies whether a constant is case-insensitive. Default value is false. It means it is case sensitive by default.
<?php define("MESSAGE","Hello The New Tutorial PHP<br>"); echo MESSAGE; //Create a constant with case-insensitive name: define("MESSAGE1","Hello Hello The New Tutorial.com PHP",true);//not case sensitive echo MESSAGE1, "</br>"; echo message1; ?>