Error Handling in PHP

 

Error handling is a very important part of creating web applications. If your code is not efficient, then you may receive error messages. Also, it will put your application in a risky position. Let us examine some methods of dealing with errors in PHP.

Default Error Handling in PHP

By default, error handling in PHP is quite simple. An error message along with line number, file name and a message is sent to the web browser.

Error Handling Methods:

Following are the error handling methods:

1.Basic Error Handling Using die() statements

Consider the following example in which we are trying to open a file which doesn’t exist in htdocs folder.

Example

<?php

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

?>

Output

Warning: fopen(welcome.txt): failed to open stream: No such file or directory in C:\xampp\htdocs\test.php on line 2

Solution

Use the following code containing die() . If file doesn’t exist then it will show error.

Code

<?php

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

 die("File not found");

} else {

 $file=fopen("welcome.txt","r");

}

?>

Output

File not found

 

The way we dealt with the earlier code is not always the preferred approach, but a simpler method in which we use a straight forward error mechanism. Hence, an alternative approach for handling errors are the PHP functions.

2.Error Reporting

Here we will see that How to Create a Custom Error Handler in PHP

A custom error handler is basically a special function which is called when an event occurs or says error occurs.

Syntax

Error_function(error_level,error_message,error_file,error_line,error_context)

 

This function handles at least 2 parameters, namely error level, and error message. The other three parameters are optional. Description of these parameters is as follows:

 

Error_level	It is a compulsory parameter. It specifies the error report level. It should be a numeric value.
Error_message	Required. Specifies the error message for the user-defined error It is also mandatory parameter. It determines the error message for the user defined errors.
Error_file	It is an optional parameter. It shows the file name in which the error has occurred.
Error_line	It is also an optional field. It specifies the line numbers of the lines in which error has occurred.
Error_context	It is also optional. Here you may specify the array which contains variables and values at the time of error occurring.

What Are Error Report Levels?

User defined error handler can be used to report different types of error. Let’s have a look on the list of error report levels:

E_Warning	It shows non-fatal run time errors. It doesn’t stop execution of the script.
E_Notice	They are basically run time notices. They are displayed when there is some error within the script.
E_USER_ERROR	It is a user generated error. It is similar to E_ERROR and trigger_error()
E_USER_WARNING	It is a typical non-fatal warning which is user generated. It is similar to E_WARNING.
E_USER_NOTICE	It is also a user generated notice. Likewise it is similar to E_Notice.
E_RECOVERABLE_ERROR	It is a catchable fatal error. It is similar to E_ERROR with the difference that it can be fixed using user defined handle.
E_ALL	It will deal with every warning and error.

3.Custom Errors & Triggers

Handling of Errors by Creating Custom Function

We will now create a user defined function to handle errors. Now lets create a function to handle errors:

function customError($errno, $errstr) {

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

 echo "Ending Script";

 die();

}

When the above code is triggered, it shows an error message with the error level. It then displays them and halts the script execution. We have just created an error handling function. Now we have to finalize when it should be triggered.

How to Set Error Handler?

In PHP, we have a built-in error handler. We will now make our function the default error handler. It is also possible that we can change the error handler occurrence specific to a few errors. But for now, we will use custom error handler for all errors.

Set_error_handler(“customError”);

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.

Let’s consider the example below, where we are testing the error handler. We are trying to display such a variable in this example which actually doesn’t exist.

Code

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

<?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);

?>

Output

Error: [8] Undefined variable: test

Trigger an Error

Its significance is when users can input data so that errors are triggered when an illegal input occurs. We have a predefined function in php for this purpose called trigger_error().

Example

Lets consider the example below, in this case if test is bigger than 1, it will trigger the error.

<?php

$test=2;

if ($test>1) {

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

}

?>

Output

Notice: Value must be 1 or below in C:\xampp\htdocs\test.php on line 5

These errors can be triggered wherever you feel necessary to trigger.

Example

Let’s consider another example in which if a test variable is bigger than 1, then E_USER_WARNING occurs. If it happens, then a custom error handler is utilized.

<?php

//error handler function

function customError($errno, $errstr) {

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

 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);

}

?>

Output:

Error: [512] Value must be 1 or below

Ending Script

4. Error Reporting

Up till now, we have covered errors triggering and custom errors handling. Let’s start our next topic, Error Logging.

Error Logging

In PHP, error log is sent to the logging system of the server. It is also dependent on php.ini file. Luckily, we have a predefined function in PHP for this purpose called error_log().

By using this function, you may send error logs to a remote destination. Many developers find this a good way to send error messages by email to themselves. Hence, they get notified in this way.

Send an Error Message by E-Mail

In the example below, we will send email with error message. In case the error occurs, it will end the script.

<?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);

}

?>

Output

Error: [512] Value must be 1 or below

Webmaster has been notified.

At the specified email address, the email will be received as below:

Error: [512] Value must be 1 or below

It should be noted that regular errors should be logged by using default logging system. It is not a good approach to adopt with all errors.

Errors and Logging

Let’s consider the errors and their descriptions about logging.

E_ERROR	They are fatal errors which occur at run time. As a result of such errors, execution of the script is stopped. These type of errors most commonly occur due to memory allocation type problems.
E_WARNING	They are also runtime warnings but they never cause halting of execution of script.
E_PARSE	They are generated by the parser. They occur at compile time mostly.
E_NOTICE	They also at run time. They are run time notices.
E_CORE_ERROR	They are fatal errors which usually occur during the startup. They are similar to E_ERROR with a difference that it is generated by core PHP.
E_CORE_WARNING	It is similar to E_WARNING. These are the warnings of non fatal errors. These warnings also occur at the time of startup. It is also generated by core PHP.
E_COMPILE_ERROR	They are similar to E_ERROR. They are basically fatal errors which occurs at compile time. Difference between this and E_ERROR is that it is generated by Zend Engine.
E_COMPILE_WARNING	They are non fatal errors, or say compile time warnings. It is similar to E_WARNING but with a difference that it is generated by Zend engine.
E_USER_ERROR	They are user generated error messages. It is similar to E_ERROR with a difference that It is generated by PHP function trigger_error().
E_USER_WARNING	They are warning messages generated by users. It is similar to E_WARNING with a difference that it is also generated by trigger_error() function.
E_USER_NOTICE	User-generated notice message. This is like an E_NOTICE, except it is generated in PHP code by using the PHP function trigger_error().
E_STRICT	You should enable this to get suggestions by PHP . It will definitely lead to best compatibility of your code.
E_DEPRECATED	They are run time notices. By enabling this, you may receive warnings which will not work in future versions.
E_RECOVERABLE_ERROR	It is a fatal error which is catchable. It is an indication of a typical serious error.
E_USER_DEPRECATED	These are the warning messages generated by the user. It is much similar to E_DEPRECATED but with a difference that it is generated by function trigger_error()

 

Well, I hope you found this post on PHP error handling useful. If you’re confused about anything discussed here, or you’ve got a comment, fire away. I’d love to discuss PHP error handling with you 🙂