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:
If the file does not exist you might get an error like this:
No such file or directory in C:\webfolder\test.php on line 2
To avoid that the user gets an error message like the one above, we test if the file exist before we try to access it:
die("File not found");
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):
|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:
|2||E_WARNING||Non-fatal run-time errors. Execution of the script is not halted|
|8||E_NOTICE||Run-time notices. The script found something that might be an error, but could also happen when running a script normally|
|256||E_USER_ERROR||Fatal user-generated error. This is like an E_ERROR set by the programmer using the PHP function trigger_error()|
|512||E_USER_WARNING||Non-fatal user-generated warning. This is like an E_WARNING set by the programmer using the PHP function trigger_error()|
|1024||E_USER_NOTICE||User-generated notice. This is like an E_NOTICE set by the programmer using the PHP function trigger_error()|
|4096||E_RECOVERABLE_ERROR||Catchable fatal error. This is like an E_ERROR but can be caught by a user defined handle (see also set_error_handler())|
|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:
echo "Error: [$errno] $errstr
echo "Ending Script";
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.