PHP set_error_handler() Function - GeeksforGeeks

PHP set_error_handler() Function

Last Updated : 30 Oct, 2026

The set_error_handler() function in PHP sets a user-defined function to handle errors that occur during script execution. It allows developers to customize error handling, log error messages, and respond to specific error levels.

  • It can handle errors such as warnings, notices, and user-generated errors.
  • It accepts a callback function and an optional error-level mask.
  • The custom handler can receive the error type, message, filename, and line number.
  • It cannot handle certain errors, including E_ERROR, E_PARSE, E_CORE_ERROR, and E_COMPILE_ERROR.

Syntax:

set_error_handler(?callable $callback, int $error_levels = E_ALL): ?callable

Parameters:

  • $callback: The function to call when a matching error occurs. Pass null to remove the active custom handler.
  • $error_levels: An optional bitmask specifying which error levels the handler should process. The default is E_ALL.

Return value: Returns the previously defined error handler, or null if PHP's built-in handler was active.

Example 1: Using set_error_handler()

The following example defines a custom error handler and uses trigger_error() to generate a user-level warning.

PHP 
<?php
function customErrorHandler($errno, $errstr, $errfile, $errline) {
    echo "Error: $errstr\n";
    echo "File: $errfile\n";
    echo "Line: $errline\n";
}

set_error_handler("customErrorHandler");

trigger_error("Invalid input provided", E_USER_WARNING);
?>

Note: The filename and line number depend on where the error occurs.

  • customErrorHandler() defines how the error should be handled.
  • set_error_handler() registers the function as the custom error handler.
  • trigger_error() generates a user-level warning.
  • PHP passes the error details to the registered handler.

Example 2: Handling Specific Error Levels

The $error_levels parameter allows developers to register a handler for specific error types.

PHP 
<?php
function customErrorHandler($errno, $errstr) {
    echo "Custom handler: $errstr";
}

set_error_handler("customErrorHandler", E_USER_WARNING);

trigger_error("This is a warning", E_USER_WARNING);
?>

Here, the custom handler is registered for E_USER_WARNING. Other error levels are not handled by this callback and generally fall back to PHP's standard error handler.

Example 3: Restoring the Previous Error Handler

The restore_error_handler() function restores the error handler that was active before the most recent set_error_handler() call.

PHP 
<?php
function customErrorHandler($errno, $errstr) {
    echo "Custom handler: $errstr\n";
}

set_error_handler("customErrorHandler");

trigger_error("First warning", E_USER_WARNING);

restore_error_handler();

trigger_error("Second warning", E_USER_WARNING);
?>

The exact format of the second warning depends on the PHP configuration and execution environment.

The first warning is processed by the custom handler. After restore_error_handler() is called, the previous handler is restored, so the second warning uses PHP's standard error handling.

Best Practices

  • Use a custom error handler to centralize error handling and logging.
  • Specify appropriate error levels when registering the handler to handle only relevant errors.
  • Check error_reporting() when necessary to respect the current error reporting configuration.
  • Avoid displaying sensitive error details to end users in production environments.
  • Log errors with relevant details, such as the error message, filename, and line number.
  • Use restore_error_handler() when the custom handler is no longer needed.
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