Introduction to php exception and error management
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This document discusses error management in PHP. It describes different types of errors like compile-time errors, fatal errors, recoverable errors, and warnings. It also discusses how to configure error reporting using php.ini directives like error_reporting, display_errors, and log_errors. Additionally, it explains how to handle errors programmatically using set_error_handler() and exception handling. The document provides an example of throwing and catching exceptions using try/catch blocks. Finally, it discusses lazy loading of classes using the __autoload() function in PHP.
![2. Handling Errors
• The set_error_handler() function sets a user-defined function to
handle errors.
• Eg: set_error_handler(error_function,error_types)
<?php
//error handler function
function customError($errno, $errstr, $errfile,
$errline)
{
echo "<b>Custom error:</b> [$errno] $errstr<br
/>";
echo " Error on line $errline in $errfile<br />";
echo "Ending Script";
die();
}
//set error handler
set_error_handler("customError");
$test=2;
//trigger error
if ($test>1)
{
trigger_error("A custom error has been
triggered");
}](https://image.slidesharecdn.com/introductiontophp-exceptionanderrormanagement-140404234844-phpapp01/85/Introduction-to-php-exception-and-error-management-6-320.jpg)
Introduction to php exception and error management
- 1. Error Management in PHP
- 2. Types of errors Compile-time errors Errors detected by the parser while it is compiling a script. Cannot be trapped from within the script itself. Fatal errors Errors that halt the execution of a script. Cannot be trapped. Recoverable errors Errors that represent significant failures, but can still be handled in a safe way. Warnings Recoverable errors that indicate a run-time fault. Do not halt the execution of the script. Notices Indicate that an error condition occurred, but is not necessarily significant. Do not halt the execution of the script.
- 3. Error Reporting • By default, PHP reports any errors it encounters to the script’s output unless you control it as follows 1. Configuring Php.ini 2. Handling Errors by setting set_error_handler()
- 4. 1. Configuring Php.ini – Several configuration directives in the php.ini file allow you to fine tune how—and which—errors are reported. – error_reporting, – display_errors – log_errors. You can find these in php.ini file
- 5. 1. Configuring Php.ini • error_reporting – determines which errors are reported by PHP – Eg: error_reporting=E_ALL & ~E_NOTICE • display_errors – if turned on, errors are outputted to the script’s output; this is not desirable in a production environment, as everyone will be able to see your scripts’ errors. Eg: display_errors = ON • log_errors, – which causes errors to be written to your web server’s error log, so that only developers can utilise it and end users will not be informed of same – Eg:log_errors,=ON
- 6. 2. Handling Errors • The set_error_handler() function sets a user-defined function to handle errors. • Eg: set_error_handler(error_function,error_types) <?php //error handler function function customError($errno, $errstr, $errfile, $errline) { echo "<b>Custom error:</b> [$errno] $errstr<br />"; echo " Error on line $errline in $errfile<br />"; echo "Ending Script"; die(); } //set error handler set_error_handler("customError"); $test=2; //trigger error if ($test>1) { trigger_error("A custom error has been triggered"); }
- 7. Exception Handling in PHP
- 8. Exception Handling in PHP • Exceptions provide an error control mechanism that is more fine- grained than traditional PHP fault handling.There are several key differences between “regular” PHP errors and exceptions: • Exceptions are objects, created (or “thrown”) when an error occurs • Exceptions can be handled at different points in a script’s execution, and different types of exceptions can be handled by separate portions of a script’s code • All unhandled exceptions are fatal • Exceptions can be thrown from the __construct method on failure • Exceptions change the flow of the application
- 9. The Basic Exception Class • As we mentioned in the previous paragraph, exceptions are objects that must be direct or indirect (for example through inheritance) instances of the Exception base class. • The latter is built into PHP itself, and is declared as follows:
- 10. The Basic Exception Class class Exception { // The error message associated with this exception protected $message = ’Unknown Exception’; // The error code associated with this exception protected $code = 0; // The pathname of the file where the exception occurred protected $file; // The line of the file where the exception occurred protected $line; // Constructor function __construct ($message = null, $code = 0); // Returns the message final function getMessage(); // Returns the error code final function getCode(); // Returns the file name final function getFile(); // Returns the file line final function getLine(); // Returns an execution backtrace as an array final function getTrace(); // Returns a backtrace as a string final function getTraceAsString(); // Returns a string representation of the exception function __toString(); }
- 11. The Basic Exception Class • Almost all of the properties of an Exception are automatically filled in for you by the interpreter—generally speaking, you only need to provide a message and a code, and all the remaining information will be taken care of for you. • Since Exception is a normal (if built-in) class, you can extend it and effectively create your own exceptions, thus providing your error handlers with any additional information that your application requires.
- 12. Throwing Exceptions • Exceptions are usually created and thrown when an error occurs by using the throw construct: if ($error) { throw new Exception ("This is my error"); } • Exceptions then “bubble up” until they are either handled by the script or cause a fatal exception • The handling of exceptions is performed using a try...catch block:
- 13. Example try { if ($error) { throw new Exception ("This is my error"); } } catch (Exception $e) { echo $e->getMessage(); } • In the example above, any exception that is thrown inside the try{} block is going to be caught and passed on the code inside the catch{} block, where it can be handled
- 14. Lazy Loading
- 15. Lazy Loading • Prior to PHP 5, if you try to create an object on an undefined class(perhaps that class is written on another file which you forgot to include) would cause a fatal error. • This meant that you needed to include all of the class files that you might need, rather than loading them as they were needed • To solve this problem, PHP 5 features an “autoload” facility that makes it possible to implement “lazy loading”, or loading of classes on-demand only • When we try to create an object of undefined class PHP will try to call the __autoload() global magic function so that the script may be given an opportunity to load it.
- 16. __autoload() - Example function __autoload($class) { // Require PEAR-compatible classes require_once(“$class.php”) } $obj = new SomeClass();
- 17. __autoload() - Example function __autoload($class) { // Require PEAR-compatible classes require_once(“$class.php”) } $obj = new SomeClass(); You tried to create an object of SomeClass. But you forgot that someClass is defined in another page called SomeClass.php
- 18. __autoload() - Example function __autoload($class) { // Require PEAR-compatible classes require_once(“$class.php”) } $obj = new SomeClass(); When you tried to do so, PHP will automatically calls __autoload() which will have an argument ie the class name for which object we tried to create
- 19. __autoload() - Example function __autoload($class) { // Require PEAR-compatible classes require_once(“$class.php”) } $obj = new SomeClass(); We are including the file called “someClass.php” The advantage of lazy loading is that we can include files upon its requirement only rather than including all the files unnecessarily
- 20. Questions? “A good question deserve a good grade…”
- 21. End of day
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