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.

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<?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.

Code Examples / Notes » language.operators.errorcontrol

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.

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 ... }

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...

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.

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.

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...

Error Control Operators

Code Examples / Notes » language.operators.errorcontrol

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