restore_exception_handler
set_exception_handler
Error Handling Functions
PHP Manual

# set_error_handler

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

set_error_handler — Sets a user-defined error handler function

### Description

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

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`, 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.

  bool handler ( int `$errno` , string `$errstr` [, string `$errfile` [, int `$errline` [, array `$errcontext` ]]] )
  `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.

  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
--- | ---
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() & $errno)) {
// This error code is not included in error_reporting
return;
}
switch ($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

restore_exception_handler
set_exception_handler
Error Handling Functions
PHP Manual