Php set error handler () function

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(PHP 4 >= 4.0.1, PHP 5)

set_error_handler -- Sets a user-defined error handler function

Syntax

mixed set_error_handler ( callback error_handler [, int error_types] )

Sets a user function (error_handler) to handle errors in a script. Returns a string containing the previously defined error handler (if any), or FALSE on error. If the previous handler was a class method, this function will return an indexed array with the class and the method name.

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()).

The second parameter error_types was introduced in PHP 5 and 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.

The user function needs to accept two parameters: the error code, and a string describing the error. From PHP 4.0.2, three optional parameters are supplied: the filename in which the error occurred, the line number in which the error occurred, and the context in which the error occurred (an array that points to the active symbol table at the point the error occurred). The function can be shown as: 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.

Note: Instead of a function name, an array containing an object reference and a method name can also be supplied. (Since PHP 4.3.0)

Note: 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.

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

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


<?php

// redefine the user error constants - PHP 4 only
define("FATAL", E_USER_ERROR);
define("ERROR", E_USER_WARNING);
define("WARNING", E_USER_NOTICE);

// set the error reporting level for this script
error_reporting(FATAL | ERROR | WARNING);

// error handler function
function myErrorHandler($errno, $errstr, $errfile, $errline) 
{
  switch ($errno) {
  case FATAL:
    echo "<b>FATAL</b> [$errno] $errstr<br />\n";
    echo "  Fatal error in line $errline of file $errfile";
    echo ", PHP " . PHP_VERSION . " (" . PHP_OS . ")<br />\n";
    echo "Aborting...<br />\n";
    exit(1);
    break;
  case ERROR:
    echo "<b>ERROR</b> [$errno] $errstr<br />\n";
    break;
  case WARNING:
    echo "<b>WARNING</b> [$errno] $errstr<br />\n";
    break;
  default:
    echo "Unkown error type: [$errno] $errstr<br />\n";
    break;
  }
}

// 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",
      FATAL);
  }

  if (!is_array($vect)) {
    trigger_error("Incorrect input vector, array of values expected", ERROR);
    return null;
  }

  for ($i=0; $i<count($vect); $i++) {
    if (!is_numeric($vect[$i]))
      trigger_error("Value at position $i is not a number, using 0 (zero)", 
        WARNING);
    $temp[$i] = log($scale) * $vect[$i];
  }
  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, generating a warning
echo "----\nvector b - a warning (b = log(PI) * a)\n";
$b = scale_by_log($a, M_PI);
print_r($b);

// this is trouble, we pass a string instead of an array
echo "----\nvector c - an error\n";
$c = scale_by_log("not array", 2.3);
var_dump($c);

// this is a critical error, log of zero or negative number is undefined
echo "----\nvector d - fatal error\n";
$d = scale_by_log($a, -2.5);

?>

The above example will output:

vector a
Array
(
    [0] => 2
    [1] => 3
    [2] => foo
    [3] => 5.5
    [4] => 43.3
    [5] => 21.11
)
----
vector b - a warning (b = log(PI) * a)
<b>WARNING</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 - an error
<b>ERROR</b> [512] Incorrect input vector, array of values expected<br />
NULL
----
vector d - fatal error
<b>FATAL</b> [256] log(x) for x <= 0 is undefined, you used: scale = -2.5<br />
  Fatal error in line 36 of file trigger_error.php, PHP 4.0.2 (Linux)<br />
Aborting...<br />

It is important to remember that the standard PHP error handler is completely bypassed. 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.

Note: 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.

Note: The second parameter error_types was introduced in PHP 5.

See also error_reporting(), restore_error_handler(), trigger_error(), error level constants, and information about the callback type.

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Php set error handler syntax tutorial

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