Custom error function php

PHP Error Handling

Error handling in PHP is simple. An error message with filename, line number and a message describing the error is sent to the browser.

PHP Error Handling

When creating scripts and web applications, error handling is an important part. If your code lacks error checking code, your program may look very unprofessional and you may be open to security risks.

This tutorial contains some of the most common error checking methods in PHP.

We will show different error handling methods:

Basic Error Handling: Using the die() function

The first example shows a simple script that opens a text file:

Example

If the file does not exist you might get an error like this:

Warning: fopen(mytestfile.txt) [function.fopen]: failed to open stream:
No such file or directory in C:\webfolder\test.php on line 2

To prevent the user from getting an error message like the one above, we test whether the file exist before we try to access it:

Example

if(file_exists(«mytestfile.txt»)) $file = fopen(«mytestfile.txt», «r»);
> else die(«Error: The file does not exist.»);
>
?>

Now if the file does not exist you get an error like this:

The code above is more efficient than the earlier code, because it uses a simple error handling mechanism to stop the script after the error.

However, simply stopping the script is not always the right way to go. Let’s take a look at alternative PHP functions for handling errors.

Creating a Custom Error Handler

Creating a custom error handler is quite simple. We simply create a special function that can be called when an error occurs in PHP.

This function must be able to handle a minimum of two parameters (error level and error message) but can accept up to five parameters (optionally: file, line-number, and the error context):

Syntax

Parameter	Description
error_level	Required. Specifies the error report level for the user-defined error. Must be a value number. See table below for possible error report levels
error_message	Required. Specifies the error message for the user-defined error
error_file	Optional. Specifies the filename in which the error occurred
error_line	Optional. Specifies the line number in which the error occurred
error_context	Optional. Specifies an array containing every variable, and their values, in use when the error occurred

Error Report levels

These error report levels are the different types of error the user-defined error handler can be used for:

Value	Constant	Description
1	E_ERROR	A fatal run-time error. Execution of the script is stopped
2	E_WARNING	A non-fatal run-time error. Execution of the script is not stopped
8	E_NOTICE	A run-time notice. The script found something that might be an error, but could also happen when running a script normally
256	E_USER_ERROR	A fatal user-generated error. This is like an E_ERROR, except it is generated by the PHP script using the function trigger_error()
512	E_USER_WARNING	A non-fatal user-generated warning. This is like an E_WARNING, except it is generated by the PHP script using the function trigger_error()
1024	E_USER_NOTICE	A user-generated notice. This is like an E_NOTICE, except it is generated by the PHP script using the function trigger_error()
2048	E_STRICT	Not strictly an error.
8191	E_ALL	All errors and warnings (E_STRICT became a part of E_ALL in PHP 5.4)

Now lets create a function to handle errors:

The code above is a simple error handling function. When it is triggered, it gets the error level and an error message. It then outputs the error level and message and terminates the script.

Now that we have created an error handling function we need to decide when it should be triggered.

Set Error Handler

The default error handler for PHP is the built in error handler. We are going to make the function above the default error handler for the duration of the script.

It is possible to change the error handler to apply for only some errors, that way the script can handle different errors in different ways. However, in this example we are going to use our custom error handler for all errors:

Since we want our custom function to handle all errors, the set_error_handler() only needed one parameter, a second parameter could be added to specify an error level.

Example

Testing the error handler by trying to output variable that does not exist:

//error handler function
function customError($errno, $errstr) echo «Error: [$errno] $errstr»;
>

//set error handler
set_error_handler(«customError»);

The output of the code above should be something like this:

Trigger an Error

In a script where users can input data it is useful to trigger errors when an illegal input occurs. In PHP, this is done by the trigger_error() function.

Example

In this example an error occurs if the «test» variable is bigger than «1»:

The output of the code above should be something like this:

An error can be triggered anywhere you wish in a script, and by adding a second parameter, you can specify what error level is triggered.

• E_USER_ERROR — Fatal user-generated run-time error. Errors that can not be recovered from. Execution of the script is halted
• E_USER_WARNING — Non-fatal user-generated run-time warning. Execution of the script is not halted
• E_USER_NOTICE — Default. User-generated run-time notice. The script found something that might be an error, but could also happen when running a script normally

Example

In this example an E_USER_WARNING occurs if the «test» variable is bigger than «1». If an E_USER_WARNING occurs we will use our custom error handler and end the script:

//error handler function
function customError($errno, $errstr) echo «Error: [$errno] $errstr
«;
echo «Ending Script»;
die();
>

//set error handler
set_error_handler(«customError»,E_USER_WARNING);

//trigger error
$test=2;
if ($test>=1) trigger_error(«Value must be 1 or below»,E_USER_WARNING);
>
?>

The output of the code above should be something like this:

Now that we have learned to create our own errors and how to trigger them, lets take a look at error logging.

Error Logging

By default, PHP sends an error log to the server’s logging system or a file, depending on how the error_log configuration is set in the php.ini file. By using the error_log() function you can send error logs to a specified file or a remote destination.

Sending error messages to yourself by e-mail can be a good way of getting notified of specific errors.

Send an Error Message by E-Mail

In the example below we will send an e-mail with an error message and end the script, if a specific error occurs:

//error handler function
function customError($errno, $errstr) echo «Error: [$errno] $errstr
«;
echo «Webmaster has been notified»;
error_log(«Error: [$errno] $errstr»,1,
«someone@example.com»,»From: webmaster@example.com»);
>

//set error handler
set_error_handler(«customError»,E_USER_WARNING);

//trigger error
$test=2;
if ($test>=1) trigger_error(«Value must be 1 or below»,E_USER_WARNING);
>
?>

The output of the code above should be something like this:

And the mail received from the code above looks like this:

This should not be used with all errors. Regular errors should be logged on the server using the default PHP logging system.

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Custom error function php

A User defined Exception class can be defined by extending the built-in Exception class. The members and properties below, show what is accessible within the child class that derives from the built-in Exception class.

Example #1 The Built in Exception class

class Exception implements Throwable
protected $message = ‘Unknown exception’ ; // exception message
private $string ; // __toString cache
protected $code = 0 ; // user defined exception code
protected $file ; // source filename of exception
protected $line ; // source line of exception
private $trace ; // backtrace
private $previous ; // previous exception if nested exception

public function __construct ( $message = » , $code = 0 , Throwable $previous = null );

final private function __clone (); // Inhibits cloning of exceptions.

final public function getMessage (); // message of exception
final public function getCode (); // code of exception
final public function getFile (); // source filename
final public function getLine (); // source line
final public function getTrace (); // an array of the backtrace()
final public function getPrevious (); // previous exception
final public function getTraceAsString (); // formatted string of trace

// Overrideable
public function __toString (); // formatted string for display
>
?>

If a class extends the built-in Exception class and re-defines the constructor, it is highly recommended that it also call parent::__construct() to ensure all available data has been properly assigned. The __toString() method can be overridden to provide a custom output when the object is presented as a string.

Note:

Exceptions cannot be cloned. Attempting to clone an Exception will result in a fatal E_ERROR error.

Example #2 Extending the Exception class

/**
* Define a custom exception class
*/
class MyException extends Exception
// Redefine the exception so message isn’t optional
public function __construct ( $message , $code = 0 , Throwable $previous = null ) // some code

// make sure everything is assigned properly
parent :: __construct ( $message , $code , $previous );
>

// custom string representation of object
public function __toString () return __CLASS__ . «: [ < $this ->code > ]: < $this ->message > \n» ;
>

public function customFunction () echo «A custom function for this type of exception\n» ;
>
>

/**
* Create a class to test the exception
*/
class TestException
public $var ;

const THROW_NONE = 0 ;
const THROW_CUSTOM = 1 ;
const THROW_DEFAULT = 2 ;

function __construct ( $avalue = self :: THROW_NONE )

switch ( $avalue ) case self :: THROW_CUSTOM :
// throw custom exception
throw new MyException ( ‘1 is an invalid parameter’ , 5 );
break;

case self :: THROW_DEFAULT :
// throw default one.
throw new Exception ( ‘2 is not allowed as a parameter’ , 6 );
break;

default:
// No exception, object will be created.
$this -> var = $avalue ;
break;
>
>
>

// Example 1
try $o = new TestException ( TestException :: THROW_CUSTOM );
> catch ( MyException $e ) < // Will be caught
echo «Caught my exception\n» , $e ;
$e -> customFunction ();
> catch ( Exception $e ) < // Skipped
echo «Caught Default Exception\n» , $e ;
>

// Continue execution
var_dump ( $o ); // Null
echo «\n\n» ;

// Example 2
try $o = new TestException ( TestException :: THROW_DEFAULT );
> catch ( MyException $e ) < // Doesn't match this type
echo «Caught my exception\n» , $e ;
$e -> customFunction ();
> catch ( Exception $e ) < // Will be caught
echo «Caught Default Exception\n» , $e ;
>

// Continue execution
var_dump ( $o ); // Null
echo «\n\n» ;

// Example 3
try $o = new TestException ( TestException :: THROW_CUSTOM );
> catch ( Exception $e ) < // Will be caught
echo «Default Exception caught\n» , $e ;
>

// Continue execution
var_dump ( $o ); // Null
echo «\n\n» ;

// Example 4
try $o = new TestException ();
> catch ( Exception $e ) < // Skipped, no exception
echo «Default Exception caught\n» , $e ;
>

// Continue execution
var_dump ( $o ); // TestException
echo «\n\n» ;
?>

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