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:

Example Usage of the defined() Function

<‌?php

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

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

Try it Yourself »

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.

Practice

What does the defined() function do in PHP?

It checks whether a function is defined or not.It accepts a string containing the name of the variable and returns true, if the variable is defined.It returns true if the given string exists as a constant and false otherwise.It is used for arithmetic operations.It deletes the defined variable.