   #PHP Manual Error Handling and Logging Functions restore_error_handler
   trigger_error

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                               set_error_handler

   (PHP 4 >= 4.0.1)
   set_error_handler --  Sets a user-defined error handler function.

Description

   string set_error_handler ( callback error_handler)

   Sets a user function (error_handler) to handle errors in a script.
   Returns the previously defined error handler (if any), or FALSE on
   error. 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 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).

     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 and E_COMPILE_WARNING.

   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);
   ?>

   And when you run this sample script, the output will be :
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.

   See also error_reporting(), restore_error_handler(), trigger_error(),
   and error level constants.
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