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# set_error_handler

(PHP 4 )

set_error_handler -- Sets a user-defined error handler function.

## Description

``string set_error_handler` (string 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 2 parameters: the error code, and a string describing the error. From PHP 4.0.2, an additional 3 optional parameters are supplied: the filename in which the error occured, the line number in which the error occured, and the context in which the error occured (an array that points to the active symbol table at the point the error occurred).

The example below shows the handling of internal execptions 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.

See also error_reporting(), restore_error_handler(), trigger_error(), user_error()

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