PHP error handling, PHP error _php Tutorial

PHP error handling, PHP error

In PHP, the default error handling is simple. An error message is sent to the browser with a file name, line number, and a message that describes the error.

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 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 will get an error like this:

Warning:fopen (Welcome.txt) [function.fopen]: failed to open stream:no such file or directory in c:webfoldertest.php on Li NE 2

To prevent the user from getting a similar error message, we detect if the file exists before accessing the file:

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

File not found

The above code 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	Description
Error_level	Necessary. Specifies the error reporting level for user-defined errors. Must be a number. See the table below: Error reporting levels.
Error_message	Necessary. Specifies error messages for user-defined errors.
Error_file	Optional. Specifies the name of the file where 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 are handled by user-defined error handlers:

value	Constants	Description
2	E_warning	A non-fatal run-time error. Script execution is not paused.
8	E_notice	Run-time notice. Occurs when a script discovers a possible error, 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. (In PHP 5.4, E_strict becomes 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 ";d ie ();}

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 up error handlers

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 a second parameter can be added to define the error level.

Instance

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

 
  Error: [$errno] $errstr ";} Set error Handlerset_error_handler ("Customerror");//trigger Errorecho ($test);? >

The output of the above code is as follows:

Error: [8] Undefined Variable:test

Trigger Error

Where the user enters data in the script, it is useful to trigger an error when the user's input is invalid. In PHP, this task is done by the Trigger_error () function.

Instance

In this example, if the "test" variable is greater than "1", an error occurs:

 
  1) {Trigger_error ("Value must be 1 or below");}? >

The output of the above code is as follows:

Notice:value must be 1 or Belowin c:webfoldertest.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. Occurs when a script discovers a possible error, but it may also occur when the script is running correctly.

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: [$errno] $errstr
"echo" ending Script ";d ie ();} Set error Handlerset_error_handler ("Customerror", e_user_warning);//trigger error$test=2;if ($test >1) {Trigger_ Error ("Value must be 1 or below", e_user_warning);}? >

The output of the above code is as follows:

Error: [1] Value must be or belowending Script

Now that we've learned how to create our own errors and how to trigger them, let's look at the error record.

Error logging

By default, PHP sends an error record to the server's record 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: [$errno] $errstr
"; echo" Webmaster have been notified "; Error_log (" Error: [$errno] $errstr ", 1," someone@example.com "," From: Webmaster@example.com ");} Set error Handlerset_error_handler ("Customerror", e_user_warning);//trigger error$test=2;if ($test >1) {Trigger_ Error ("Value must be 1 or below", e_user_warning);}? >

The output of the above code is as follows:

Error: [+] Value must be 1 or belowwebmaster have been notified

Messages received from the above code are as follows:

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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