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Last updated: Sat, 07 Jan 2012

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Fehler-Kontroll-Operatoren

PHP unterstützt einen Operator zur Fehlerkontrolle: Das @-Symbol. Stellt man das @ in PHP vor einen Ausdruck werden alle Fehlermeldungen, die von diesem Ausdruck erzeugt werden könnten, ignoriert.

Ist das track_errors -Feature aktiviert, werden alle Fehlermeldungen, die von diesem Ausdruck erzeugt werden, in der Variablen $php_errormsg gespeichert. Da diese Variable mit jedem neuen Auftreten eines Fehlers überschrieben wird, sollte man sie möglichst bald nach Verwendung des Ausdrucks überprüfen, wenn man mit ihr arbeiten will.

<?php
/* Beabsichtigter Dateifehler */
$my_file = @file ('nicht_vorhandene_Datei') or
    die ("Datei konnte nicht geöffnetwerden: Fehler war:'$php_errormsg'");

// Das funktioniert bei jedem Ausdruck, nicht nur bei Funktionen:
$value = @$cache[$key]; 
// erzeugt keine Notice, falls der Index $key nicht vorhanden ist.

?>

Hinweis: Der @-Operator funktioniert nur bei Ausdrücken. Eine einfache Daumenregel: wenn Sie den Wert von etwas bestimmen können, dann können Sie den @-Operator davor schreiben. Zum Beispiel können Sie ihn vor Variablen, Funktionsaufrufe und vor include() setzen, vor Konstanten und so weiter. Nicht verwenden können Sie diesen Operator vor Funktions- oder Klassendefinitionen oder vor Kontrollstrukturen wie zum Beispiel if und foreach und so weiter.

Siehe auch error_reporting() und den Abschnitt über Error Handling and Logging Functions.

Hinweis:

Der @ Fehler-Kontroll-Operator verhindert jedoch keine Meldungen, welche aus Fehlern beim Parsen resultieren.

Warnung

Zum gegenwärtigen Zeitpunkt deaktiviert der "@" Fehler-Kontrolloperator die Fehlermeldungen selbst bei kritischen Fehlern, die die Ausführung eines Skripts beenden. Unter anderem bedeutet das, wenn Sie "@" einer bestimmten Funktion voranstellen, diese aber nicht zur Verfügung steht oder falsch geschrieben wurde, Ihr PHP-Skript einfach beendet wird, ohne Hinweis auf die Ursache.



add a note add a note User Contributed Notes
Fehler-Kontroll-Operatoren
John Chilton
09-Jul-2007 12:18
To omelnyk:

It also says:

A simple rule of thumb is: if you can take the value of something, you can prepend the @ operator to it. For instance, you can prepend it to variables, function and include() calls....

"...you can prepend it to variables..."

I happen to use it with variables all the time, and have also noticed the (IMHO) odd result when trying to stifle errors when asking isset() about a nonexistent variable. However, it does make more sense to use @isset($foo) than isset(@$foo) to me anyway...
omelnyk at gmail dot com
18-May-2007 05:05
To webmaster at speedy dot co dot il:

it's not a bug. As the manual says, the @-operator works only on expressions, and isset() takes a variable, not expression, as its argument.
nospam at blog dot fileville dot net
03-Jan-2007 08:58
If you want to log all the error messages for a php script from a session you can use something like this:
<?php
 session_start();
  function error($error, $return=FALSE) {
      global $php_errormsg;
      if(isset($_SESSION['php_errors'])) {
        $_SESSION['php_errors'] = array();    
    }
  $_SESSION['php_errors'][] = $error; // Maybe use $php_errormsg
  if($return == TRUE) {
    $message = "";
       foreach($_SESSION['php_errors'] as $php_error) {
          $messages .= $php_error."\n";
     } 
    return $messages; // Or you can use use $_SESSION['php_errors']
  }
}
?>
Hope this helps someone...
13-Dec-2006 02:52
error_reporting()==0 for detecting the @ error suppression assumes that you did not set the error level to 0 in the first place.

However, typically if you want to set your own error handler, you would set the error_reporting to 0. Therefore, an alternative to detect the @ error suppression is required.
programming at kennebel dot com
13-Oct-2006 03:38
To suppress errors for a new class/object:

<?php
// Tested: PHP 5.1.2 ~ 2006-10-13

// Typical Example
$var = @some_function();

// Class/Object Example
$var = @new some_class();

// Does NOT Work!
//$var = new @some_class(); // syntax error
?>

I found this most useful when connecting to a
database, where i wanted to control the errors
and warnings displayed to the client, while still
using the class style of access.
me at hesterc dot fsnet dot co dot uk
03-Mar-2005 05:25
If you wish to display some text when an error occurs, echo doesn't work. Use print instead. This is explained on the following link 'What is the difference between echo and print?':

http://www.faqts.com/knowledge_base/view.phtml/aid/1/fid/40

It says "print can be used as part of a more complex expression where echo cannot".

Also, you can add multiple code to the result when an error occurs by separating each line with "and". Here is an example:

<?php
$my_file = @file ('non_existent_file') or print 'File not found.' and $string = ' Honest!' and print $string and $fp = fopen ('error_log.txt', 'wb+') and fwrite($fp, $string) and fclose($fp);
?>

A shame you can't use curly brackets above to enclose multiple lines of code, like you can with an if statement or a loop. It could make for a single long line of code. You could always call a function instead.
frogger at netsurf dot de
26-Dec-2004 05:19
Better use the function trigger_error() (http://de.php.net/manual/en/function.trigger-error.php)
to display defined notices, warnings and errors than check the error level your self. this lets you write messages to logfiles if defined in the php.ini, output
messages in dependency to the error_reporting() level and suppress output using the @-sign.
webmaster __AT__ digitalanime __DOT__ nl
19-May-2004 12:10
Someone over here wanted to know how to use the @ in your error handler... It's easy:

<?php
function my_error_handler(.......)
{
  if(error_reporting() == 0) // error_reporting() = 0, so it was called with @ in front of it
  {
    // do nothing
  }
  else
  {
   // do something
  }
}
?>
manicdepressive at mindless dot com
29-Feb-2004 01:44
taking the value of a non existant element:

   $foo = @$array['not_here']

will work as described, setting $foo to NULL,

but taking a *reference* to a non-existant element:

   $foo =& @$array['not_here']

will create the element with a NULL value, which $foo will then referece.

  -- code till dawn, mark meves
sdavey at datalink dot net dot au
30-Nov-2003 01:26
To suppress error warnings for functions that use the error operator '@' in your own error handlers, I found a sentence on the set_error_handler() page that explains it:
http://www.php.net/manual/en/function.set-error-handler.php

To paraphrase, it says that PHP temporarily sets the value of error_reporting() to 0 when in the error handler.

So, if you have the following:

$fp = @fopen("non-existent-file", "r");

when your custom error handler function is called, you can check the value of error_reporting() like this:

function handler($type, $str, $file, $line, $info) {
    // don't respond to the error if it
    // was suppressed with a '@'
    if (error_reporting() == 0) return;

    // otherwise, handle the error
    ...
}
john-at-n0-spam-foobar-dot-nl
25-Jul-2003 07:04
With set_error_handler() you bypass the standard error handler, which takes care of @.

if (!($fp = @fopen('not_a_file', 'r')))
  trigger_error("Can't open file!", E_USER_WARNING);

... generates ...

Warning: fopen("not_a_file", "r") - No such file or directory in index.php on line 19.
User Warning : Can't open file! in index.php on line 20.

... when I use my own error handler. With the standard error handler I only get the second warning.

If someone knows how to use @ with your own error handler, let me know.
psychohist at aol dot com
04-Jul-2003 10:59
if you create a new variable by assigning to it the error
suppressed value of an unset variable, the new variable
will be set, with a value of (I believe) null:

$new_variable                // previously not set
    = @$nonexistent_variable; // also not set

$next_variable = $new_variable // no warning generated
25-Apr-2003 03:24
It should be noted that suppressed error reporting is inherited, so to speak.

Consider this function:
function warning() {
    $return = 10 / 0;
    return $return;
}

This line will produce a warning;
var_dump(warning());

While these will not:
var_dump(@warning());
@var_dump(warning());

This might not be so obvious for some people; I know I didn't expect this behaviour.
19-Oct-2002 08:00
To suppress errors for a method inside a class, place the @ operator before the object and not before the method name.

// DO:
@$this->foo($bar);

// DON'T:
$this->@foo($bar);
drm at gerard dot yoursite dot nl
21-Aug-2002 12:50
When you check if an index of an array is set, you imply that the array itself already exists.

So
if ( isset ( $array [ 'index' ] ) ) {
}

would generate a notice if $array is not defined, but not if $array _is_ defined, but the index 'index' not.

And so on for nested arrays ofcourse
webmaster at speedy dot co dot il
07-Jul-2002 02:31
I don't know if this is a feature or bug, but this doesn't work:

if (!(isset(@$GLOBALS['SPEEDY_GLOBAL_VARS']['PAGE_NAME'])))

On the other hand, this works:

if (!(@isset($GLOBALS['SPEEDY_GLOBAL_VARS']['PAGE_NAME'])))

Regards,
Uri.
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Operatoren zur Programmausführung> <Vergleichs-Operatoren
Last updated: Sat, 07 Jan 2012