Defined()

Introduction to the defined() Function

The defined() function in PHP is used to check if a constant is defined or not.

Usage of the defined() Function

The defined() function takes one argument, which is the name of the constant whose existence is to be checked. The function returns a boolean value, true if the constant exists, and false if it does not.

Example Usage of the defined() Function

Here's an example of how the defined() function can be used in PHP:

<?php

define("GREETING", "Hello, world!");

if (defined("GREETING")) {
  echo GREETING;
} else {
  echo "GREETING is not defined!";
}

In this example, the defined() function is used to check if the constant GREETING has been defined or not. Since it has been defined in the previous line, the echo statement will output Hello, world!.

Conclusion

In conclusion, the defined() function in PHP is a simple yet useful tool for checking the existence of a constant in your code. It takes one argument, the name of the constant, and returns a boolean value indicating whether or not the constant has been defined.