Error Handler Functions
Setting a custom error handler in PHP offers a heightened level of control and flexibility over the default error-handling mechanism. There are various reasons for using a custom error handler:
- Instead of showing a generic error message, you can define tailored responses for different error types. This can provide users with friendlier or more helpful feedback.
- While PHP can log errors out-of-the-box, a custom handler allows you to log additional data or integrate with third-party logging tools, helping in more detailed diagnostics.
- Rather than exposing sensitive system information with default error messages (especially in a production environment), custom error handlers can show generic messages while logging the detailed error internally.
Setting an Error Handler
Creating a custom error handler in PHP involves defining a custom function and then telling PHP to use this function for handling errors. Let's walk through the process.
The first step is to use the set_error_handler() function. This function accepts the name of a function to call when an error occurs.
set_error_handler("customErrorHandler");In this example, we're telling PHP to run a function called customErrorHandler. This function can accept up to five parameters (though not all are mandatory)
| Parameter Name | Required | Description |
|---|---|---|
$errno | Yes | Specifies the error type. This parameter can have values like E_ERROR, E_WARNING, E_NOTICE, etc. |
$errstr | Yes | Describes the error in the form of a string message. |
$errfile | No | Specifies the filename in which the error occurred. |
$errline | No | Specifies the line number in the file where the error occurred. |
$errcontext | No | An array that points to the active symbol table at the point the error occurred. Rarely used in practice. |
Here's an example of our customErrorHandler function.
function customErrorHandler($errno, $errstr, $errfile, $errline) {
echo "<b>Custom Error:</b> [$errno] $errstr<br>";
echo " Error on line $errline in $errfile<br>";
echo "Ending Script";
die(); // End the script
}For demonstration purposes, we can trigger an error to see our custom error handler in action.
echo $undefinedVariable; // This will cause an errorWhen the error is triggered, instead of the default PHP error message, you will see the output from the customErrorHandler function.
<b>Custom Error:</b> [2] Undefined variable $undefinedVariable<br> Error on line 15 in script.php<br>Ending ScriptThings to Note
- The custom error handler will not handle fatal errors. Fatal errors will continue to be handled by PHP's default error mechanism.
- You can further extend the custom error handler to log errors to a file or a database, send email notifications, or integrate with monitoring services.
- It's a good practice to avoid displaying detailed error messages on a production site for security reasons. Instead, log the detailed errors and display a generic message to the user.
Key Takeaways
- Custom error handlers give developers the flexibility to define how errors are processed and presented, allowing for more tailored responses.
- The custom error handler function can accept up to five parameters:
$errno(error type),$errstr(error message),$errfile(error file),$errline(error line), and$errcontext(error context). - Use the
set_error_handler()function to designate a function as the custom error handler. - Custom error handlers can't handle fatal errors. These are still managed by PHP's default mechanism.