PHP - Introduction to PHP Error Handling

Introduction to PHPIntroduction to PHP
Error HandlingError Handling

TypesTypes
There are 12 unique error types, which can
be grouped into 3 main categories:
• Informational (Notices)
• Actionable (Warnings)
• Fatal

Informational ErrorsInformational Errors
• Harmless problem, and can be avoided through
use of explicit programming.
e.g. use of an undefined variable, defining a string
without quotes, etc.

Actionable ErrorsActionable Errors
• Indicate that something clearly wrong has
happened and that action should be taken.
e.g. file not present, database not available,
missing function arguments, etc.

Fatal ErrorsFatal Errors
• Something so terrible has happened during
execution of your script that further
processing simply cannot continue.
e.g. parsing error, calling an undefined
function, etc.

Identifying ErrorsIdentifying Errors
E_STRICT Feature or behaviour is depreciated (PHP5).
E_NOTICE Detection of a situation that could indicate a problem,
but might be normal.
E_USER_NOTICE User triggered notice.
E_WARNING Actionable error occurred during execution.
E_USER_WARNING User triggered warning.
E_COMPILE_WARNING Error occurred during script compilation (unusual)
E_CORE_WARNING Error during initialization of the PHP engine.
E_ERROR Unrecoverable error in PHP code execution.
E_USER_ERROR User triggered fatal error.
E_COMPILE_ERROR Critical error occurred while trying to read script.
E_CORE_ERROR Occurs if PHP engine cannot startup/etc.
E_PARSE Raised during compilation in response to syntax error
notice
warning
fatal

Causing errorsCausing errors
• It is possible to cause PHP at any point in your
script.
trigger_error($msg,$type);
e.g.
…
if (!$db_conn) {
trigger_error(‘db conn
failed’,E_USER_ERROR);
}
…

PHP Error HandlingPHP Error Handling

Customizing ErrorCustomizing Error
HandlingHandling
• Generally, how PHP handles errors is defined
by various constants in the installation (php.ini).
• There are several things you can control in
your scripts however..

Set error reportingSet error reporting
settingssettings
error_reporting($level)
This function can be used to control which
errors are displayed, and which are simply
ignored. The effect only lasts for the duration
of the execution of your script.

Set error reporting settingsSet error reporting settings
<?php
// Turn off all error reporting
error_reporting(0);
// Report simple running errors
error_reporting(E_ERROR | E_WARNING | E_PARSE);
// Reporting E_NOTICE can be good too (to report uninitialized
// variables or catch variable name misspellings ...)
error_reporting(E_ERROR | E_WARNING | E_PARSE | E_NOTICE);
// Report all errors except E_NOTICE
error_reporting(E_ALL ^ E_NOTICE);
// Report ALL PHP errors
error_reporting(E_ALL);
?>

Set error reportingSet error reporting
settingssettings
• Hiding errors is NOT a solution to a problem.
• It is useful, however, to hide any errors
produced on a live server.
• While developing and debugging code,
displaying all errors is highly recommended!

Suppressing ErrorsSuppressing Errors
• The special @ operator can be used to
suppress function errors.
• Any error produced by the function is
suppressed and not displayed by PHP
regardless of the error reporting setting.

$db = @mysql_connect($h,$u,
$p);
if (!$db) {
trigger_error(‘blah’,E_USER_
ERROR);
}

$db = @mysql_connect($h,$u,$p);
if (!$db) {
trigger_error(blah.',E_USER_ERROR
);
}
Attempt to connect to
database. Suppress error
notice if it fails..

if (!$db) {
trigger_error(‘blah’,E_USER_ERROR);
}
Since error is suppressed, it
must be handled gracefully
somewhere else..

• Error suppression is NOT a solution to a
problem.
• It can be useful to locally define your own
error handling mechanisms.
• If you suppress any errors, you must check
for them yourself elsewhere.

Custom Error HandlerCustom Error Handler
• You can write your own function to handle
PHP errors in any way you want.
• You simply need to write a function with
appropriate inputs, then register it in your
script as the error handler.
• The handler function should be able to
receive 4 arguments, and return true to
indicate it has handled the error…

function err_handler(
$errcode,$errmsg,$file,$lineno) {
echo ‘An error has occurred!<br />’;
echo “file: $file<br />”;
echo “line: $lineno<br />”;
echo “Problem: $errmsg”;
return true;
}

return true;
}
The handler must have 4 inputs..
1.error code
2.error message
3.file where error occurred
4.line at which error occurred

return true;
}
Any PHP statements can be
executed…

return true;
}
return true;
Return true to let PHP know
that the custom error handler
has handled the error OK.

• The function then needs to be registered as your
custom error handler:
set_error_handler(‘err_handler’);
• You can ‘mask’ the custom error handler so it
only receives certain types of error. e.g. to
register a custom handler just for user triggered
errors:
set_error_handler(‘err_handler’,
E_USER_NOTICE | E_USER_WARNING | E_USER_ERROR);

• A custom error handler is never passed
E_PARSE, E_CORE_ERROR or
E_COMPILE_ERROR errors as these are
considered too dangerous.
• Often used in conjunction with a ‘debug’
flag for neat combination of debug and
production code display..

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PHP - Introduction to PHP Error Handling

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