Sets a user-defined error handler function

# set_error_handler

(PHP 4 >= 4.0.1, PHP 5, PHP 7, PHP 8)

set_error_handler — Sets a user-defined error handler function

### Description

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

Sets a user function (`callback`) to handle errors in a script.

This function can be used to define custom error handlers during runtime, for example in applications which need to do file/data cleanup when a critical error happens, or when triggering an error in response to certain conditions (using trigger_error()).

It is important to remember that the standard PHP error handler is completely bypassed for the error types specified by `error_levels` unless the callback function returns `false`. error_reporting() settings will have no effect and the error handler will be called regardless - however, it's still possible to read the current value of error_reporting and act appropriately.

Also note that it is the handler's responsibility to stop the script's execution if necessary by calling exit(). If the error-handler function returns, script execution will continue with the next statement after the one that caused an error.

The following error types cannot be handled with a user defined function: `E_ERROR`, `E_PARSE`, `E_CORE_ERROR`, `E_CORE_WARNING`, `E_COMPILE_ERROR`, `E_COMPILE_WARNING` independent of where they were raised, and most of `E_STRICT` raised in the file where set_error_handler() is called.

If errors occur before the script is executed (e.g. on file uploads) the custom error handler cannot be called since it is not registered at that time.

### Parameters

`callback`

  If `null` is passed, the handler is reset to its default state. Otherwise, the handler is a callback with the following signature:

  handler(
  int `$errno`,
  string `$errstr`,
  string `$errfile` = ?,
  int `$errline` = ?,
  array `$errcontext` = ?
  ): bool
  `errno`
    The first parameter, `errno`, will be passed the level of the error raised, as an integer.
  `errstr`
    The second parameter, `errstr`, will be passed the error message, as a string.
  `errfile`
    If the callback accepts a third parameter, `errfile`, it will be passed the filename that the error was raised in, as a string.
  `errline`
    If the callback accepts a fourth parameter, `errline`, it will be passed the line number where the error was raised, as an integer.
  `errcontext`
    If the callback accepts a fifth parameter, `errcontext`, it will be passed an array that points to the active symbol table at the point the error occurred. In other words, `errcontext` will contain an array of every variable that existed in the scope the error was triggered in. User error handlers must not modify the error context.
    Warning

    This parameter has been DEPRECATED as of PHP 7.2.0, and REMOVED as of PHP 8.0.0. If the function defines this parameter without a default, an error of "too few arguments" will be raised when it is called.

  If the function returns `false` then the normal error handler continues.

`error_levels`

  Can be used to mask the triggering of the `callback` function just like the error_reporting ini setting controls which errors are shown. Without this mask set the `callback` will be called for every error regardless to the setting of the error_reporting setting.

### Return Values

Returns the previously defined error handler (if any) as a callable. If the built-in error handler is used `null` is returned.

### Changelog

Version | Description
--- | ---
8.0.0 | `errcontext` was removed, and will no longer be passed to user callbacks.
7.2.0 | `errcontext` became deprecated. Usage of this parameter now emits an `E_DEPRECATED` notice.

### Examples

Example #1 Error handling with set_error_handler() and trigger_error()

The example below shows the handling of internal exceptions by triggering errors and handling them with a user defined function:

`<?php
// error handler function
function myErrorHandler($errno, $errstr, $errfile, $errline)
{
if (!(error_reporting() & $errno)) {
// This error code is not included in error_reporting, so let it fall
// through to the standard PHP error handler
return false;
}
// $errstr may need to be escaped:
$errstr = htmlspecialchars($errstr);
switch ($errno) {
case E_USER_ERROR:
echo "<b>My ERROR</b> [$errno] $errstr<br />\n";
echo " Fatal error on line $errline in file $errfile";
echo ", PHP " . PHP_VERSION . " (" . PHP_OS . ")<br />\n";
echo "Aborting...<br />\n";
exit(1);
case E_USER_WARNING:
echo "<b>My WARNING</b> [$errno] $errstr<br />\n";
break;
case E_USER_NOTICE:
echo "<b>My NOTICE</b> [$errno] $errstr<br />\n";
break;
default:
echo "Unknown error type: [$errno] $errstr<br />\n";
break;
}
/* Don't execute PHP internal error handler */
return true;
}
// function to test the error handling
function scale_by_log($vect, $scale)
{
if (!is_numeric($scale) || $scale <= 0) {
trigger_error("log(x) for x <= 0 is undefined, you used: scale = $scale", E_USER_ERROR);
}
if (!is_array($vect)) {
trigger_error("Incorrect input vector, array of values expected", E_USER_WARNING);
return null;
}
$temp = array();
foreach($vect as $pos => $value) {
if (!is_numeric($value)) {
trigger_error("Value at position $pos is not a number, using 0 (zero)", E_USER_NOTICE);
$value = 0;
}
$temp[$pos] = log($scale) * $value;
}
return $temp;
}
// set to the user defined error handler
$old_error_handler = set_error_handler("myErrorHandler");
// trigger some errors, first define a mixed array with a non-numeric item
echo "vector a\n";
$a = array(2, 3, "foo", 5.5, 43.3, 21.11);
print_r($a);
// now generate second array
echo "----\nvector b - a notice (b = log(PI) * a)\n";
/* Value at position $pos is not a number, using 0 (zero) */
$b = scale_by_log($a, M_PI);
print_r($b);
// this is trouble, we pass a string instead of an array
echo "----\nvector c - a warning\n";
/* Incorrect input vector, array of values expected */
$c = scale_by_log("not array", 2.3);
var_dump($c); // NULL
// this is a critical error, log of zero or negative number is undefined
echo "----\nvector d - fatal error\n";
/* log(x) for x <= 0 is undefined, you used: scale = $scale" */
$d = scale_by_log($a, -2.5);
var_dump($d); // Never reached
?>`

The above example will output something similar to:

    vector a
    Array
    (
        [0] => 2
        [1] => 3
        [2] => foo
        [3] => 5.5
        [4] => 43.3
        [5] => 21.11
    )
    ----
    vector b - a notice (b = log(PI) * a)
    <b>My NOTICE</b> [1024] Value at position 2 is not a number, using 0 (zero)<br />
    Array
    (
        [0] => 2.2894597716988
        [1] => 3.4341896575482
        [2] => 0
        [3] => 6.2960143721717
        [4] => 49.566804057279
        [5] => 24.165247890281
    )
    ----
    vector c - a warning
    <b>My WARNING</b> [512] Incorrect input vector, array of values expected<br />
    NULL
    ----
    vector d - fatal error
    <b>My ERROR</b> [256] log(x) for x <= 0 is undefined, you used: scale = -2.5<br />
      Fatal error on line 35 in file trigger_error.php, PHP 5.2.1 (FreeBSD)<br />
    Aborting...<br />

### See Also

- ErrorException
- error_reporting() - Sets which PHP errors are reported
- restore_error_handler() - Restores the previous error handler function
- get_error_handler() - Gets the user-defined error handler function
- trigger_error() - Generates a user-level error/warning/notice message
- error level constants

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