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Error HandlingPHPMay-2007 : [#] PHP Error Handling.

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Presentation on theme: "Error HandlingPHPMay-2007 : [#] PHP Error Handling."— Presentation transcript:

1 Error HandlingPHPMay-2007 : [#] PHP Error Handling

2 Error HandlingPHPMay-2007 : [#] Types There are 12 unique error types, which can be grouped into 3 main categories: Informational (Notices) Actionable (Warnings) Fatal

3 Error HandlingPHPMay-2007 : [#] Informational 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. See class example error1.php

4 Error HandlingPHPMay-2007 : [#] Actionable 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. See class example error2.php

5 Error HandlingPHPMay-2007 : [#] Fatal 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. See class example error3.php

6 Error HandlingPHPMay-2007 : [#] Identifying 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

7 Error HandlingPHPMay-2007 : [#] Causing 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); } …

8 Error HandlingPHPMay-2007 : [#] PHP Error Handling

9 Error HandlingPHPMay-2007 : [#] Customizing Error Handling 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..

10 Error HandlingPHPMay-2007 : [#] 1. Set error reporting settings 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.

11 Error HandlingPHPMay-2007 : [#] 1. Set error reporting settings See class example error4.php

12 Error HandlingPHPMay-2007 : [#] 1. Set error reporting settings 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!

13 Error HandlingPHPMay-2007 : [#] 2. Suppressing Errors The 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.

14 Error HandlingPHPMay-2007 : [#] 2. Suppressing Errors $db if (!$db) { trigger_error(blah,E_USER_ERROR); }

15 Error HandlingPHPMay-2007 : [#] 2. Suppressing Errors $db if (!$db) { trigger_error(blah.',E_USER_ERROR); } $db Attempt to connect to database. Suppress error notice if it fails..

16 Error HandlingPHPMay-2007 : [#] 2. Suppressing Errors $db if (!$db) { trigger_error(blah.',E_USER_ERROR); } if (!$db) { trigger_error(blah,E_USER_ERROR); } Since error is suppressed, it must be handled gracefully somewhere else..

17 Error HandlingPHPMay-2007 : [#] 2. Suppressing Errors 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 msut check for them yourself elsewhere.

18 Error HandlingPHPMay-2007 : [#] 3. Custom 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…

19 Error HandlingPHPMay-2007 : [#] 3. Custom Error Handler function err_handler( $errcode,$errmsg,$file,$lineno) { echo An error has occurred! ; echo file: $file ; echo line: $lineno ; echo Problem: $errmsg; return true; }

20 Error HandlingPHPMay-2007 : [#] 3. Custom Error Handler function err_handler( $errcode,$errmsg,$file,$lineno) { echo An error has occurred! ; echo file: $file ; echo line: $lineno ; echo Problem: $errmsg; return true; } $errcode,$errmsg,$file,$lineno) { The handler must have 4 inputs.. 1.error code 2.error message 3.file where error occurred 4.line at which error occurred

21 Error HandlingPHPMay-2007 : [#] 3. Custom Error Handler function err_handler( $errcode,$errmsg,$file,$lineno) { echo An error has occurred! ; echo file: $file ; echo line: $lineno ; echo Problem: $errmsg; return true; } echo An error has occurred! ; echo file: $file ; echo line: $lineno ; echo Problem: $errmsg; Any PHP statements can be executed…

22 Error HandlingPHPMay-2007 : [#] 3. Custom Error Handler function err_handler( $errcode,$errmsg,$file,$lineno) { echo An error has occurred! ; echo file: $file ; echo line: $lineno ; echo Problem: $errmsg; return true; } return true; Return true to let PHP know that the custom error handler has handled the error OK.

23 Error HandlingPHPMay-2007 : [#] 3. Custom Error Handler 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);

24 Error HandlingPHPMay-2007 : [#] 3. Custom Error Handler 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.. See class example error5.php

25 Error HandlingPHPMay-2007 : [#] Review Various different error types exist in PHP. The error handling system is highly flexible, and your own error handling methods can be developed.


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