Operatori di confronto
NB The @ operator doesn't work when throwing errors as exceptions using the ErrorException class
Operatori di controllo errori
PHP supporta un operatore di controllo dell'errore: il carattere at (@). Quando prefisso ad una espressione in PHP, qualunque messaggio di errore che potesse essere generato da quella espressione sarà ignorato.
Se la caratteristica track_errors è abilitata, qualsiasi messaggio di errore generato dall'espressione sarà salvato nella variabile globale $php_errormsg. Questa variabile sarà sovrascritta ad ogni errore, così controllatela subito se volete usarla.
<?php
/* Errore di file intenzionale */
$my_file = @file ('file_inesistente') or
die ("Apertura del file fallita: l'errore è '$php_errormsg'");
// questo funziona per qualsiasi espressione, non solo funzioni:
$value = @$cache[$key];
// non verrà generata una notifica se l'indice $key non esiste.
?>
Nota: L'operatore @ funziona solo sulle espressioni. Una semplice regola è: se potete prendere il valore di qualcosa, potete anteporre ad esso l'operatore @. Per esempio, potete anteporre esso a variabili, funzioni e chiamate ad include(), costanti, e così via. non potete anteporre esso a definizioni di funzioni o classi, o strutture condizionali come if e foreach, e così via.
Vedere anche error_reporting() e la sezione del manuale Gestione degli errori e funzioni di log.
Avviso
Attualmente il prefisso operatore di controllo dell'errore "@" disabiliterà la restituzione di errori per errori critici che interromperanno l'esecuzione dello script. Tra le altre cose, questo significa che se state usando "@" per sopprimere errori da una certa funzione ed essa non è disponibile oppure è stata scritta male, lo script terminerà senza dare indicazioni sul perché.
add a note
User Contributed NotesOperatori di controllo errori
beatngu
27-May-2008 11:29
27-May-2008 11:29
lewis [@t] hcoms [dot] co [dot] uk
02-Apr-2008 09:38
02-Apr-2008 09:38
@John Chilton
"I happen to use it with variables all the time, and have also noticed the (IMHO) odd result when trying to stifle errors when asking isset() about a nonexistent variable. However, it does make more sense to use @isset($foo) than isset(@$foo) to me anyway..."
Using the @ symbol with isset() is useless. This is because isset() will not return an error if the variable is not existent (otherwise it would be pretty useless).
root at mantoru dot de
17-Oct-2007 09:13
17-Oct-2007 09:13
The @ operator can also be prepended to literals (like strings), as they're also statements -- it will suppress any notice about uninitialized variables. If you want to silence a more complex expression (@ is unary), use braces.
<?php
// variable interpolation
$str = @"Then I said: '$maybeunset'.";
// integer stuffs
$result = @2 * 3 / 0; // = @(2) * 3 / 0 - WRONG (warning)
$result = @(2 * 3 / 0); // RIGHT (no warning), $result is false
?>
@John Chilton's post: As omelnyk said, isset is a language construct and NOT a function, and an @ token is not allowed there. @isset makes no sense, because under ANY circumstances isset stays quiet.
Also, "using it with variables all the time" is a VERY bad idea, because it will make your code EXTREMELY slow. Crank your error_reporting down then.
John Chilton
09-Jul-2007 12:18
09-Jul-2007 12:18
To omelnyk:
It also says:
A simple rule of thumb is: if you can take the value of something, you can prepend the @ operator to it. For instance, you can prepend it to variables, function and include() calls....
"...you can prepend it to variables..."
I happen to use it with variables all the time, and have also noticed the (IMHO) odd result when trying to stifle errors when asking isset() about a nonexistent variable. However, it does make more sense to use @isset($foo) than isset(@$foo) to me anyway...
omelnyk at gmail dot com
18-May-2007 05:05
18-May-2007 05:05
To webmaster at speedy dot co dot il:
it's not a bug. As the manual says, the @-operator works only on expressions, and isset() takes a variable, not expression, as its argument.
nospam at blog dot fileville dot net
03-Jan-2007 08:58
03-Jan-2007 08:58
If you want to log all the error messages for a php script from a session you can use something like this:
<?php
session_start();
function error($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
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
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
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
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
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
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, $info) {
// don't respond to the error if it
// was suppressed with a '@'
if (error_reporting() == 0) return;
// otherwise, handle the error
...
}
john-at-n0-spam-foobar-dot-nl
25-Jul-2003 07:04
25-Jul-2003 07:04
With set_error_handler() you bypass the standard error handler, which takes care of @.
if (!($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
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
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 $array _is_ defined, but the index 'index' not.
And so on for nested arrays ofcourse
webmaster at speedy dot co dot il
07-Jul-2002 02:31
07-Jul-2002 02:31
I don't know if this is a feature or bug, but this doesn't work:
if (!(isset(@$GLOBALS['SPEEDY_GLOBAL_VARS']['PAGE_NAME'])))
On the other hand, this works:
if (!(@isset($GLOBALS['SPEEDY_GLOBAL_VARS']['PAGE_NAME'])))
Regards,
Uri.