# set_error_handler

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

set_error_handler — Sets a user-defined error handler function

### Description

set_error_handler ( callable `$error_handler` [, int `$error_types` = E_ALL | E_STRICT ] ) : mixed

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

This function can be used for defining your own way of handling errors during runtime, for example in applications in which you need to do cleanup of data/files when a critical error happens, or when you need to trigger an error under 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_types` unless the callback function returns `FALSE`. error_reporting() settings will have no effect and your error handler will be called regardless - however you are still able to read the current value of error_reporting and act appropriately. Of particular note is that this value will be 0 if the statement that caused the error was prepended by the @ error-control operator.

Also note that it is your responsibility to die() if necessary. 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

`error_handler`

  A callback with the following signature. `NULL` may be passed instead, to reset this handler to its default state. Instead of a function name, an array containing an object reference and a method name can also be supplied.

  handler ( int `$errno` , string `$errstr` [, string `$errfile` [, int `$errline` [, array `$errcontext` ]]] ) : bool
  `errno`
    The first parameter, `errno`, contains the level of the error raised, as an integer.
  `errstr`
    The second parameter, `errstr`, contains the error message, as a string.
  `errfile`
    The third parameter is optional, `errfile`, which contains the filename that the error was raised in, as a string.
  `errline`
    The fourth parameter is optional, `errline`, which contains the line number the error was raised at, as an integer.
  `errcontext`
    The fifth parameter is optional, `errcontext`, which is 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 handler must not modify error context.
    Warning

    This parameter has been DEPRECATED as of PHP 7.2.0. Relying on it is highly discouraged.

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

`error_types`

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

### Return Values

Returns a string containing the previously defined error handler (if any). If the built-in error handler is used `NULL` is returned. `NULL` is also returned in case of an error such as an invalid callback. If the previous error handler was a class method, this function will return an indexed array with the class and the method name.

### Changelog

Version | Description
--- | ---
7.2.0 | `errcontext` became deprecated. Usage of this parameter now emits an `E_DEPRECATED` notice.
5.5.0 | `error_handler` now accepts `NULL`.
5.2.0 | The error handler must return `FALSE` to populate $php_errormsg.

### 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() & $errno)) {
// This error code is not included in error_reporting, so let it fall
// through to the standard PHP error handler
return false;
}
switch ($errno) {
case E_USER_ERROR:
echo "<b>My ERROR</b> [$errno] $errstr<br />\n";
echo " Fatal error on line $errline in file $errfile";
echo ", PHP " . PHP_VERSION . " (" . PHP_OS . ")<br />\n";
echo "Aborting...<br />\n";
exit(1);
break;
case E_USER_WARNING:
echo "<b>My WARNING</b> [$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
- trigger_error() - Generates a user-level error/warning/notice message
- error level constants
- information about the callback type