PHP: Error Control Operators

Last updated: Fri, 06 Nov 2009

Error Control Operators

PHP supports one error control operator: the at sign (@). When prepended to an expression in PHP, any error messages that might be generated by that expression will be ignored.

If the track_errors feature is enabled, any error message generated by the expression will be saved in the variable $php_errormsg. This variable will be overwritten on each error, so check early if you want to use it.


<?php
/* Intentional file error */
$my_file = @file ('non_existent_file') or
    die ("Failed opening file: error was '$php_errormsg'");

// this works for any expression, not just functions:
$value = @$cache[$key];
// will not issue a notice if the index $key doesn't exist.

?>

Note: The @-operator works only on expressions. 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, constants, and so forth. You cannot prepend it to function or class definitions, or conditional structures such as if and foreach, and so forth.

See also error_reporting() and the manual section for Error Handling and Logging functions.

Warning

Currently the "@" error-control operator prefix will even disable error reporting for critical errors that will terminate script execution. Among other things, this means that if you use "@" to suppress errors from a certain function and either it isn't available or has been mistyped, the script will die right there with no indication as to why.

Execution Operators

Comparison Operators

Last updated: Fri, 06 Nov 2009

add a note User Contributed Notes
Error Control Operators

M. T.
11-Oct-2009 04:20


Be aware of using error control operator in statements before include() like this:



<?PHP



(@include("file.php"))

 OR die("Could not find file.php!");



?>



This cause, that error reporting level is set to zero also for the included file. So if there are some errors in the included file, they will be not displayed.

dsbeam at gmail dot com
02-Sep-2009 02:22


Though error suppression can be dangerous at times, it can be useful as well.  I've found the following statements roughly equivalent:



     if( isset( $var ) && $var === $something )

     if( @$var === $something )



EXCEPT when you're comparing against a boolean value (when $something is false).  In that case, if it's not set the conditional will still be triggered.



I've found this useful when I want to check a value that might not exist:



     if( @$_SERVER[ 'HTTP_REFERER' ] !== '/www/some/path/file' )



or when we want to see if a checkbox / radio button have been submitted with a post action



     if( @$_POST[ 'checkbox' ] === 'yes' )



Just letting you guys know my findings, :)

gerrywastaken
19-May-2009 08:46


Error suppression should be avoided if possible as it doesn't just suppress the error that you are trying to stop, but will also suppress errors that you didn't predict would ever occur. This will make debugging a nightmare.



It is far better to test for the condition that you know will cause an error before preceding to run the code. This way only the error that you know about will be suppressed and not all future errors associated with that piece of code.



There may be a good reason for using outright error suppression in favor of the method I have suggested, however in the many years I've spent programming web apps I've yet to come across a situation where it was a good solution. The examples given on this manual page are certainly not situations where the error control operator should be used.

taras dot dot dot di at gmail dot com
12-Aug-2008 03:29


I was confused as to what the @ symbol actually does, and after a few experiments have concluded the following:



* the error handler that is set gets called regardless of what level the error reporting is set on, or whether the statement is preceeded with @



* it is up to the error handler to impart some meaning on the different error levels. You could make your custom error handler echo all errors, even if error reporting is set to NONE.



* so what does the @ operator do? It temporarily sets the error reporting level to 0 for that line. If that line triggers an error, the error handler will still be called, but it will be called with an error level of 0



Hope this helps someone

beatngu
27-May-2008 09:29


NB The @ operator doesn't work when throwing errors as exceptions using the ErrorException class

nospam at blog dot fileville dot net
03-Jan-2007 07:58


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 01:52


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 01:38


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 04:25


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 04:19


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.

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Execution Operators

Comparison Operators

Last updated: Fri, 06 Nov 2009