PHP error handling

ArticleDirectory

• Syntax
• Error Report Level
• Instance
• Example
• Possible error types:
• Example
• Send error messages via email
• Syntax

Introduction: This is a detailed page for PHP error handling. It introduces PHP related knowledge, skills, experience, and some PHP source code.

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Create scripts and Web applicationsProgramError handling is an important part. If yourCodeThe absence of error detection code makes the program seem unprofessional and opens the door to security risks.

This tutorial introduces some of the most important error detection methods in PHP.

We will explain different error handling methods for you:

• Simple "Die ()" Statement
• Custom errors and error triggers
• Error Report

Basic Error Handling: Use the die () function

The first example shows a simple script for opening a text file:

 
<? PHP $ file = fopen ("welcome.txt", "R");?>
 

If the file does not exist, you will get an error similar to this:

Warning: Fopen(welcome.txt) [function. fopen]: failed to open stream: no such file or directory inC: \ webfolder \ test. phpOn Line2
 

To prevent users from getting error messages similar to the above, we can check whether the file exists before accessing the file:

 
<? Phpif (! 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 similar to this:

 
File not found
 

The above code is more effective than the previous Code because it uses a simple error handling mechanism to terminate the script after the error.

However, simply terminating the script is not always the proper method. Let's look at the alternative PHP functions used to handle errors.

Create a custom error Processor

It is very easy to create a custom error processor. We have created a dedicated function that can be called when an error occurs in PHP.

This function must be able to process at least two parameters (error level and error message), but can accept a maximum of five parameters (Optional: file, line-number, and error context ):

Syntax

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

Parameters	Description
Error_level	Required. Specifies the error report level for user-defined errors. It must be a value. See the following table: Error Report level.
Error_message	Required. Specifies an error message for a user-defined error.
Error_file	Optional. Specifies the file name in which the error occurs.
Error_line	Optional. Specifies the row number of the error.
Error_context	Optional. Define an array that contains each variable and their values when an error occurs.

Error Report Level

These error reporting levels are different types of errors that the error handler aims to handle:

Value	Constant	Description
2	E_warning	Non-fatal run-time error. Do not pause script execution.
8	E_notice	Run-time notification. An error may occur when the script runs normally.
256	E_user_error	Fatal user-generated error. This is similar to the e_error set by the programmer using the PHP function trigger_error.
512	E_user_warning	Non-fatal user-generated warning. This is similar to the e_warning set by the programmer using the PHP function trigger_error.
1024	E_user_notice	User-generated notifications. This is similar to the e_notice set by the programmer using the PHP function trigger_error.
4096	E_recoverable_error	Possible fatal errors. Similar to e_error, but can be captured by a user-defined handler. (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 to handle errors:

Function customerror ($ errno, $ errstr) {echo "<B> error: </B> [$ errno] $ errstr <br/>"; 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 we have created an error handling function. We need to determine when to trigger this function.

Set error handler

The default PHP error handler is a built-in error handler. We plan to transform the above function into the default error handler during script running.

You can modify the error handler so that it can only be applied to some errors, so that the script can handle different errors in different ways. However, in this example, we intend to use our custom error handler for all errors:

 
Set_error_handler ("customerror ");
 

Because we want our custom function to handle all errors, set_error_handler () only requires one parameter. You can add the second parameter to specify the error level.

Instance

Test the error handler by outputting a non-existent variable:

 
<? PHP // error handler functionfunction customerror ($ errno, $ errstr) {echo "<B> error: </B> [$ errno] $ errstr ";} // set error handlerset_error_handler ("customerror"); // trigger errorecho ($ test);?>
 

The output of the above Code should be similar to the following:

Error: [8] undefined variable: Test
 

Trigger Error

The location where the user inputs data in the script. It is useful to trigger errors when the user inputs are invalid. In PHP, this task is completed by trigger_error.

Example

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

 
<? PHP $ test = 2; if ($ test> 1) {trigger_error ("value must be 1 or below") ;}?>
 

The output of the above Code should be similar to the following:

 
Notice: value must be 1 or belowin c: \ webfolder \ test. php on line 6
 

You can trigger an error at any position in the script. By adding the second parameter, you can specify the trigger error level.

Possible error types:

• E_user_error-fatal User-Generated run-time error. The error cannot be recovered. Script Execution is interrupted.
• E_user_warning-Run-Time Warning generated by non-fatal users. Script execution is not interrupted.
• E_user_notice-default. User-Generated run-time notification. A possible error is found in the script, or it may occur when the script runs normally.

Example

In this example, if the "test" variable is greater than "1", the e_user_warning error occurs. If e_user_warning occurs, we will use our custom error handler and end the script:

<? PHP // error handler functionfunction customerror ($ errno, $ errstr) {echo "<B> error: </B> [$ errno] $ errstr <br/> "; echo "ending script"; die () ;}// 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 should be similar to the following:

 
Error: [512] value must be 1 or belowending script
 

Now we have learned how to create our own errors and how to punish them. Now let's look at the error records.

Error records

By default, according to The error_log configuration in PHP. ini, PHP sends an error record to the server's error record system or file. By using the error_log () function, you can send error records to specified files or remote destinations.

An error message is sent to you by email, which is a good way to receive notification of a specified error.

Send error messages via email

In the following example, if a specific error occurs, we will send an email with an error message and end the script:

<? PHP // error handler functionfunction 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 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 should be similar to the following:

 
Error: [512] value must be 1 or belowwebmaster has been notified
 

Emails received from the code above are similar to the following:

 
Error: [512] value must be 1 or below
 

This method is not suitable for all errors. Regular errors should be recorded on the server by using the default PHP record system.

Error backtracking

Definition and usage

The PHP debug_backtrace () function generates a backtrace.

This function returns an associated array. The following elements may be returned:

Name	Type	Description
Function	String	The current function name.
Line	Integer	The current row number.
File	String	The current file name.
Class	String	Current Class Name
Object	Object	Current object.
Type	String	The current call type. Possible calls: Return Value: "->"-method call Return Value: ":"-static method call Return nothing-function call
ARGs	Array	If function parameters are listed. If the referenced file lists the referenced file names.

Syntax

 
Debug_backtrace ()
 

Example

<? Phpfunction one ($ str1, $ str2) {two ("glenn", "quagmire");} function two ($ str1, $ str2) {three ("Cleveland ", "brown");} function three ($ str1, $ str2) {print_r (debug_backtrace ();} One ("Peter", "Griffin");?>
 

Output:

 
Array ([0] => array (=> C: \ webfolder \ test. PHP [Line] => 7 [function] => three [ARGs] => array ([0] => Cleveland [1] => brown )) [1] => array (=> C: \ webfolder \ test. PHP [Line] => 3 [function] => two [ARGs] => array ([0] => Glenn [1] => Quagmire )) [2] => array (=> C: \ webfolder \ test. PHP [Line] => 14 [function] => one [ARGs] => array ([0] => Peter [1] => Griffin )))
 

From: http://www.w3school.com.cn/php/php_error.asp

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