PHP Error Handling restore_exception_handler() Function

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The PHP Error Handling restore_exception_handler() function is used to restore the exception handler to its default behavior. When you use a custom exception handler, set_exception_handler() returns the previous one. It is helpful if you need a custom handler temporarily and then want PHP to handle exceptions properly. This ensures that your custom handler won't affect other parts of your program.

It is simple to use and works in unison with PHP's error-handling system. Understanding this feature helps you write more versatile and error-free programs.

Syntax

Below is the syntax of the PHP Error Handling restore_exception_handler() function −

bool restore_exception_handler()

Parameters

This function does not accept any parameter.

Return Value

The restore_exception_handler() function returns TRUE on success. And FALSE on failure.

PHP Version

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

Example 1

This program shows how to set a custom exception handler, trigger it, and then restore the default handler. It demonstrates the basic usage of the PHP Error Handling restore_exception_handler() function.

<?php
   // Custom exception handler
   function customExceptionHandler($exception) {
      echo "Custom Exception: " . $exception->getMessage() . "\n";
   }

   // Set custom handler
   set_exception_handler("customExceptionHandler");

   // Trigger an exception
   throw new Exception("This is a test exception");

   // Restore default handler 
   restore_exception_handler();
?>

Output

Here is the outcome of the following code −

Custom Exception: This is a test exception

Example 2

In the below PHP code we will use the restore_exception_handler() function for restoring the default handler dynamically. So we will create a custom handler, restore the default handler and show that the restored handler can detect any more exceptions after throwing an exception.

<?php
   // Custom exception handler
   function customExceptionHandler($exception) {
      echo "Custom Exception: " . $exception->getMessage() . "\n";
   }

   // Set custom handler
   set_exception_handler("customExceptionHandler");

   // Trigger exception handled by custom handler
   throw new Exception("First exception handled by custom handler");

   // Restore default handler
   restore_exception_handler();

   // Trigger new exception handled by default PHP handler
   throw new Exception("Second exception handled by default handler");
?> 

Output

This will generate the below output −

Custom Exception: First exception handled by custom handler

Example 3

Now the below code uses the restore_exception_handler() function within a conditional logic for selectively reverting to the default handler as per the specific logic.

<?php
   // Custom exception handler
   function customExceptionHandler($exception) {
      echo "Custom Exception: " . $exception->getMessage() . "\n";
   }

   // Set custom handler
   set_exception_handler("customExceptionHandler");

   // Trigger exception
   try {
      throw new Exception("Conditionally handled exception");
   } catch (Exception $e) {
      echo "Caught exception: " . $e->getMessage() . "\n";
      // Restore default handler based on condition
      if (true) { 
         restore_exception_handler();
      }
   }

   // Trigger another exception, handled by default handler
   throw new Exception("This will use the default handler");
?> 

Output

This will create the below output −

Caught exception: Conditionally handled exception
PHP Fatal error:  Uncaught Exception: This will use the default handler in /Users/abc/Desktop/PhpProjects/index.php:28
Stack trace:
#0 {main}
  thrown in /Users/abc/Desktop/PhpProjects/index.php on line 28