PHP - Class/Object class_exists() Function

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The PHP Class/Object class_exists() function is used to check if the given class have been defined. It returns TRUE if class_name is a defined class, FALSE otherwise. This function is useful when you have to check whether a class is available before trying to create an object of it or interact with it in any way.

Syntax

Below is the syntax of the PHP Class/Object class_exists() function −

bool class_exists ( string $class_name , bool $autoload );

Parameters

Below are the parameters of the class_exists() function −

• $class_name − It is the class name. The name is matched case insensitively.

• $autoload − Optional. If true, the function will try to autoload the class if it has not yet been declared. Defaults to true.

Return Value

The class_exists() function returns true if the class exists, and FALSE on failure.

PHP Version

First introduced in core PHP 4, the class_exists() function continues to function easily in PHP 5, PHP 7, and PHP 8.

Example 1

First we will use the PHP Class/Object class_exists() function to show the basic usage and check if a class named MyClass exists.

<?php
   // Declare class here
   class MyClass {}

   // Check of the class exists or not
   if (class_exists('MyClass')) {
       echo "MyClass exists!";
   } else {
       echo "MyClass does not exist.";
   }
?> 

Output

This will generate the below output −

MyClass exists!

Example 2

This example checks for a class called NonDeclaredClass, which has not been defined. So check if this class exists using the class_exists() function.

<?php
   // If the class does not exist
   if (class_exists('NonDeclaredClass')) {
      echo "NonDeclaredClass exists!";
   } else {
      echo "NonDeclaredClass does not exist.";
   }
?>

Output

Here is the outcome of the following code −

NonDeclaredClass does not exist.

Example 3

This example shows the autoloading functionality by trying to see a class that can be autoloaded using the class_exists() function.

<?php
   // Register an autoload function
   spl_autoload_register(function($className) {
      // Check if the class name is 'AutoLoadedClass'
      if ($className == 'AutoLoadedClass') {
          eval('class AutoLoadedClass {}');
      }
    });
    
    if (class_exists('AutoLoadedClass')) {
      echo "AutoLoadedClass exists!";
    } else {
      echo "AutoLoadedClass does not exist.";
    }
?> 

Output

This will create the below output −

AutoLoadedClass exists!

Example 4

Using the class_exists() function in the below example to disable autoloading if the class is not declared yet and it returns a false value.

<?php
   if (class_exists('AutoLoadedClass', false)) {
     echo "AutoLoadedClass exists!";
   } else {
     echo "AutoLoadedClass does not exist.";
   }
?> 

Output

Following is the output of the above code −

AutoLoadedClass does not exist.