Error Handling In PHP with all Try catch anf various runtime errors
- 2. Introduction to PHP Introduction to PHP Error Handling Error Handling
- 3. Types Types There are 12 unique error types, which can be grouped into 3 main categories: • Informational (Notices) • Actionable (Warnings) • Fatal
- 4. Informational Errors 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.
- 5. Actionable Errors 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.
- 6. Fatal Errors 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.
- 7. Identifying Errors 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
- 8. Causing errors Causing errors • It is possible to cause PHP at any point in your script. trigger_error($msg,$type); e.g. … if (!$db_conn) { trigger_error(‘db conn failed’,E_USER_ERROR); } …
- 9. PHP Error Handling PHP Error Handling
- 10. Customizing Error Customizing Error Handling Handling • Generally, how PHP handles errors is defined by various constants in the installation (php.ini). • There are several things you can control in your scripts however..
- 11. Set error reporting Set error reporting settings settings error_reporting($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.
- 12. Set error reporting settings Set 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); ?>
- 13. Set error reporting Set error reporting settings 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!
- 14. Suppressing Errors Suppressing 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.
- 15. Suppressing Errors Suppressing Errors $db = @mysql_connect($h,$u, $p); if (!$db) { trigger_error(‘blah’,E_USER_ ERROR); }
- 16. Suppressing Errors Suppressing Errors $db = @mysql_connect($h,$u,$p); if (!$db) { trigger_error(blah.',E_USER_ERROR ); } $db = @mysql_connect($h,$u,$p); Attempt to connect to database. Suppress error notice if it fails..
- 17. Suppressing Errors Suppressing Errors $db = @mysql_connect($h,$u,$p); if (!$db) { trigger_error(‘blah’,E_USER_ERROR); } Since error is suppressed, it must be handled gracefully somewhere else..
- 18. Suppressing Errors 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 must check for them yourself elsewhere.
- 19. Custom Error Handler 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…
- 20. Custom Error Handler Custom Error Handler 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; }
- 21. Custom Error Handler Custom Error Handler 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; } $errcode,$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
- 22. Custom Error Handler Custom Error Handler 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; } echo ‘An error has occurred!<br />’; echo “file: $file<br />”; echo “line: $lineno<br />”; echo “Problem: $errmsg”; Any PHP statements can be executed…
- 23. Custom Error Handler Custom Error Handler 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; Return true to let PHP know that the custom error handler has handled the error OK.
- 24. Custom Error Handler 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);
- 25. Custom Error Handler 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..
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