PHP Error

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:

    * Simple "die()" statements
    * Custom errors and error triggers
    * Error reporting
 

Basic Error Handling Using the die function

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

<?php

$file=fopen("welcome.txt","r");

?>
 
<?php

if(!file_exists("welcome.txt"))

  {

  die("File not found");

  }

else

  {

  $file=fopen("welcome.txt","r");

  }

?>

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):

error_function(error_level,error_message,

error_file,error_line,error_context) 

Error Report levels

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

function customError($errno, $errstr)

  {

  echo "<b>Error:</b> [$errno] $errstr<br />";

  echo "Ending Script";

  die();

  } 

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:

<?php

//error handler function

function customError($errno, $errstr)

  {

  echo "<b>Error:</b> [$errno] $errstr";

  }



//set error handler

set_error_handler("customError");



//trigger error

echo($test);

?> 

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.

<?php

$test=2;

if ($test>1)

{

trigger_error("Value must be 1 or below");

}

?> 

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.

Possible error types:

    * 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
 

Error Logging

By default, PHP sends an error log to the servers 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 errors messages to yourself by e-mail can be a good way of getting notified of specific errors.

<?php

//error handler function

function customError($errno, $errstr)

  {

  echo "<b>Error:</b> [$errno] $errstr<br />";

  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);

  }

?>