How to Use set_exception_handler in PHP: Simple Guide

Use set_exception_handler in PHP to define a custom function that handles uncaught exceptions globally. This function receives the exception object, letting you log errors or show friendly messages instead of default error output.

Syntax

The set_exception_handler function sets a user-defined function to handle uncaught exceptions. The handler function must accept one parameter: the exception object.

• set_exception_handler(callable $handler): callable|null
• $handler: The name of your custom function or a callable that takes the exception as an argument.
• Returns the previously defined exception handler or null if none was set.

php

set_exception_handler(function (Throwable $exception) {
    // Your code to handle the exception
});

Example

This example shows how to use set_exception_handler to catch an uncaught exception and display a custom message instead of the default error.

php

<?php

// Define a custom exception handler function
function myExceptionHandler(Throwable $exception) {
    echo "Custom Exception Handler:\n";
    echo "Exception message: " . $exception->getMessage() . "\n";
    echo "In file: " . $exception->getFile() . " on line " . $exception->getLine() . "\n";
}

// Set the custom exception handler
set_exception_handler('myExceptionHandler');

// Throw an exception without try-catch to trigger the handler
throw new Exception('Something went wrong!');

Output

Custom Exception Handler:
Exception message: Something went wrong!
In file: /path/to/script.php on line 15

Common Pitfalls

Common mistakes when using set_exception_handler include:

• Not accepting the exception parameter in the handler function, which causes errors.
• Throwing exceptions inside the handler itself, which leads to fatal errors.
• Expecting the handler to catch exceptions inside try-catch blocks; it only catches uncaught exceptions.

Always ensure your handler gracefully handles exceptions without throwing new ones.

php

<?php
// Wrong: handler without parameter
// set_exception_handler(function() {
//     echo "No exception parameter!";
// });

// Right: handler with exception parameter
set_exception_handler(function (Throwable $e) {
    echo "Handled: " . $e->getMessage();
});

Quick Reference

Function	Description
set_exception_handler(callable $handler)	Sets a global handler for uncaught exceptions.
Exception handler function	Receives the exception object as a parameter.
Returns	Previous exception handler or null if none.
Usage	Use for logging or showing friendly error messages.

Key Takeaways

Use set_exception_handler to catch all uncaught exceptions globally in PHP.

Your handler function must accept the exception object as a parameter.

Do not throw exceptions inside your exception handler to avoid fatal errors.

set_exception_handler only handles exceptions not caught by try-catch blocks.

Use it to log errors or display user-friendly messages instead of default PHP errors.