error_reporting() / set_error_handler() Since: PHP 4（2000）

Functions for setting the PHP error reporting level and controlling error handling with a custom error handler.

Syntax

// Sets or gets the error reporting level.
error_reporting($level);

// Sets a custom error handler.
set_error_handler($callback, $error_levels);

// Triggers a user-defined error.
trigger_error($message, $error_level);

// Changes a PHP configuration value. Also used to control error display.
ini_set($option, $value);

Function List

Function	Description
error_reporting($level)	Sets the error reporting level. If the argument is omitted, returns the current level. Use `E_ALL` to report all errors.
set_error_handler($callback, $error_levels)	Registers a custom function to replace PHP's default error handler. The callback receives four arguments: `$errno`, `$errstr`, `$errfile`, and `$errline`.
trigger_error($message, $error_level)	Deliberately triggers an error from your code. The second argument accepts `E_USER_NOTICE`, `E_USER_WARNING`, or `E_USER_ERROR`.
ini_set($option, $value)	Changes a PHP configuration value at runtime. Commonly used to control `display_errors` and `log_errors`.

Common Error Level Constants

Constant	Description
E_ALL	Reports all errors and warnings. Recommended for development environments.
E_ERROR	Fatal runtime errors. Script execution stops.
E_WARNING	Runtime warnings. Script execution continues.
E_NOTICE	Runtime notices, such as accessing an undefined variable.
E_DEPRECATED	Warnings about code that will stop working in a future version.
E_STRICT	Suggestions about code compatibility and future issues. Merged into `E_ALL` in PHP 8.0.

Sample Code

<?php
// Report all errors. Required setting for development environments.
error_reporting(E_ALL);
ini_set('display_errors', '1'); // Display errors on screen.

// In production, hide errors from the screen and log them instead.
error_reporting(E_ALL);
ini_set('display_errors', '0');
ini_set('log_errors', '1');
ini_set('error_log', '/var/log/php_errors.log');

// Get the current error reporting level.
$current = error_reporting();
echo $current; // Outputs '32767' when set to E_ALL.

// Set a custom error handler.
set_error_handler(function ($errno, $errstr, $errfile, $errline) {
	$date = date('Y-m-d H:i:s');
	$log = "[$date] Error($errno): $errstr — $errfile:$errline\n";
	error_log($log, 3, '/var/log/app_errors.log');
	return true; // Returning 'true' suppresses PHP's built-in error handler.
});

// Trigger a user-defined error with trigger_error().
function divide($a, $b) {
	if ($b == 0) {
		trigger_error("Division by zero attempted", E_USER_WARNING);
		return false;
	}
	return $a / $b;
}

$result = divide(10, 0); // The custom handler logs the warning.

// Report all errors except notices and deprecation warnings.
error_reporting(E_ALL & ~E_NOTICE & ~E_DEPRECATED);

Notes

error_reporting() controls which error levels PHP reports. In development, set E_ALL to display all errors. In production, disable display_errors and log errors instead. Displaying errors in production risks exposing file paths and internal application details.

set_error_handler() lets you fully customize what happens when an error occurs — logging to a file, sending email notifications, showing a custom error page, and more. Note that fatal errors such as E_ERROR and E_PARSE cannot be caught by a custom handler; use register_shutdown_function() to handle those.

For structured error handling with exceptions, see try / catch.

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