[PHP] PHP Error Handling

Error handling is an important part of creating scripts and Web applications. If your code lacks error detection coding, then the program looks unprofessional and opens the door to security risks. This tutorial introduces some of the most important error detection methods in PHP. We'll explain the different ways to handle the error: Simple "die ()" Statement custom error and error trigger error reporting Basic error handling: Using the Die () function The first example shows a simple script that opens a text file: $file =fopen ("Welcome.txt", "R"); ?> If the file does not exist, you will get an error like this: Warning:fopen (Welcome.txt) [function.fopen]: failed to open stream: No such file or directory in C:\webfolder\test.php on line 2 To prevent users from getting a similar error message, we detect if the file exists before accessing the file: if (!file_exists ("Welcome.txt")) { Die ("File not Found"); } else { $file =fopen ("Welcome.txt", "R"); }?> Now, if the file does not exist, you will get an error message like this: File not found The code above is more efficient than the previous code because it takes a simple error-handling mechanism to terminate the script after the error. However, simply terminating the script is not always the proper way. Let's look at the alternative PHP functions for handling errors. Create a custom error handler Creating a custom error handler is straightforward. We have simply created a special function that can be called when an error occurs in PHP. The function must be capable of handling at least two parameters (Error level and error message), but can accept up to five parameters (optional: File, Line-number, and error context): Grammar Error_function (Error_level,error_message, Error_file,error_line,error_context) Parameters Describe Error_level Necessary. Specifies the error reporting level for user-defined errors. Must be a number of values. See the table below: Error reporting levels. Error_message Necessary. Specifies error messages for user-defined errors. Error_file Optional. Specifies the file name in which the error occurred. Error_line Optional. Specifies the line number where the error occurred. Error_context Optional. Specifies an array that contains each variable that was used when the error occurred and their value. Error Reporting level These error reporting levels are different types of errors that the error handler is designed to handle: Value Constant Describe 2 E_warning A non-fatal run-time error. Script execution is not paused. 8 E_notice Run-time notice. The script discovers that an error may have occurred, but it may also occur when the script is running correctly. 256 E_user_error A fatal user-generated error. This is similar to the e_error that programmers use to set the PHP function Trigger_error (). 512 E_user_warning A non-fatal user-generated warning. This is similar to the e_warning that programmers use to set the PHP function Trigger_error (). 1024 E_user_notice User-generated notifications. This is similar to the e_notice that programmers use to set the PHP function Trigger_error (). 4096 E_recoverable_error A fatal error that can be caught. Similar to E_error, but can be captured by user-defined handlers. (see Set_error_handler ()) 8191 E_all All errors and warnings, except level e_strict. (In PHP 6.0,e_strict is part of E_all) Now, let's create a function that handles the error: function Customerror ($errno, $errstr) { echo "Error: [$errno] $errstr "; echo "Ending Script"; Die (); } The above code is a simple error-handling function. When it is triggered, it gets the error level and error message. It then outputs the error level and message, and terminates the script. Now that we have created an error handler, we need to determine when the function is fired. Set Error Handler The default error handler for PHP is the built-in error handler. We are going to transform the above function into the default error handler during the script run. You can modify the error handler so that it applies only to certain errors, so that the script can handle different errors in different ways. However, in this case, we intend to use our custom error handlers for all errors: Set_error_handler ("Customerror"); Since we want our custom function to handle all errors, Set_error_handler () requires only one parameter and can add a second parameter to specify the error level. Instance Test the error handler by trying to output a variable that does not exist: Error handler function function Customerror ($errno, $errstr) { echo "Error: [$errno] $errstr"; } Set Error Handler Set_error_handler ("Customerror"); Trigger Error Echo ($test); ?> The output of the above code should look like this: Custom error: [8] Undefined Variable:test Trigger Error The location of the user input data in the script is useful for triggering errors when the user's input is not valid. In PHP, this task is done by Trigger_error (). Example In this example, if the "test" variable is greater than "1", an error occurs: $test = 2; if ($test >1) { Trigger_error ("Value must be 1 or below"); }?> The output of the above code should look like this: Notice:value must be 1 or below In C:\webfolder\test.php on line 6 You can trigger an error anywhere in the script, and by adding a second parameter, you can specify the level of error that is triggered. Possible types of errors: E_user_error-Fatal user generated run-time error. The error cannot be recovered. The execution of the script was interrupted. E_user_warning-A non-fatal user-generated run-time warning. Script execution is not interrupted. E_user_notice-Default. User-generated Run-time notifications. The script found a possible error, or it might occur when the script is running normally. Example In this example, if the "test" variable is greater than "1", a e_user_warning error occurs. If 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 above code should look like this: Error: [+] Value must be 1 or below Ending Script Now that we've learned how to create our own error, and how to punish them, let's look at the error record. Error logging By default, PHP sends error records to the server's error logging system or file, based on the Error_log configuration in php.ini. By using the Error_log () function, you can send an error record to a specified file or remote destination. Sending an error message to yourself via e-mail is a good way to get notification of a specified error. Send error message via e-mail In the following example, if a specific error occurs, we will send an e-mail with an error message and end the script: 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 above code should look like this: Error: [+] Value must be 1 or below Webmaster has been notified Messages received from the above code are similar to this: Error: [+] Value must be 1 or below This method is not suitable for all errors. General errors should be logged on the server by using the default PHP record system.

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