PHP’s error handling mechanism

PHP’s error handling is relatively complicated. This article explains all the important knowledge points related to errors in PHP to make it easier to understand PHP’s error mechanism.

Basic knowledge

Before this, familiarize yourself with the basic knowledge of php error

• Predefined constants

• Runtime Configuration

• Exception

• Error handling function

Predefined constants

Defines all PHP error type constants. Each constant is an integer value. Its function is that the value (numeric value or symbol) above

is used to create a binary bit mask to Specify the error message to be reported. You can use bitwise operators to combine these values ​​or to mask certain types of errors. Please note that in php.ini, only '|', '~', '!', '^' and '&' will be parsed correctly.

From the perspective of usage, it can be divided into three categories:

1. thrown manually by the user
   E_USER_NOTICE, E_USER_WARNING, E_USER_ERROR, E_USER_DEPRECATED

2. User-caused
   E_NOTICE, E_PARSE, E_WARNING, E_ERROR, E_COMPILE_ERROR, E_COMPILE_WARNING, E_STRICT, E_RECOVERABLE_ERROR

3. 
   E_CORE_ERROR, E_CORE_WARNING

caused by the php kernel From the perspective of whether to terminate program execution, it can be divided into two categories

1. Termination of program execution
   The program terminates and enters the error handling process

2. Does not terminate program execution
   An error occurs, but the program can still continue to execute and also enter the error handling process

For error types in PHP, you can refer to this more detailed article- -Summary of PHP's error mechanism

Runtime configuration

Manual--The runtime configuration is explained in detail, but there are several configurations that still require special attention

1. error_reporting
   Reporting error type, it is recommended to configure E_ALL in the development/testing environment. After solving all types of errors, configure E_ALL in the production environment & E_DEPRECATED, indicates: report all errors except discarded errors

2. ##display_errorsWhether to display errors, configure it to false in the production environment , combined with the settings of
   error_reporting above, it means: report all errors except discarded errors, but do not display error messages.

3. ##log_errors

   Whether error logging is turned on, The production environment needs to be turned on
   . With the above two configurations, it means: report all errors except discarded errors, do not display error messages, but record (only PHP itself can Operation error information) to the log.

4. error_log

   Specify the error file(syslog is a special value)
   . The default is not Settings, in the manual:

If this configuration is not set, error messages will be sent to the SAPI error logger

Generally, if not set, it will be recorded in the apache/nginx error log. With the above three configurations, it means: report all errors except obsolete errors, do not display error information, but record it in the apache/nginx log Medium. If the file path is configured, it means:

file_dirlog. The above configurations affect the most basic performance of php errors. Of course, these configurations can be changed in the code through

or php-fpm configuration changesError handling function

There are not many error functions. The ones you should pay most attention to are

and set_exception_handler, because they can intervene in the error/exception processing process.

Let’s first look at the explanation in the PHP manual: Errors

In simple terms That is,

The default processing flow is completed through configuration, but we can set a custom error handling flow

How to handle errors that terminate script execution

As mentioned in the article, there are two kinds of errors. So how to deal with this kind of error that will terminate the execution of the script?

set_error_handler
cannot handle this kind of error, which is easy to be ignored. So we need to find another One method.This problem is basically solved like this (have not seen other solutions yet):

// 终止脚本的错误会终止脚本执行
// 即会调用已通过register_shutdown_function注册的处理函数
// 由此可注册我们的错误处理流程, 这样就进入了自定义错误流程
register_shutdown_function('FatalErrorHandle');

...

FatalErrorHandle(array $error = null) {
     
     ... 
     
     if (null === $error) {
         // 通过这种方式可以获取最后一条错误
        $error = error_get_last();
     }

     ... 
     
     // log or other logic
}

Exception

According to the explanation in w3cPHP exception handling:

When an exception is triggered, what usually happens is:

The current code state is saved
Code execution is switched to the predefined Exception handler function

• Depending on the situation, the processor may restart code execution from a saved code state, terminate script execution, or continue script execution from a location outside the code

Uncaught exceptions will terminate script execution and generate an E-ERROR error. The defined exception handling will be performed. If not, the default error handling process of PHP will be performed, which is recorded in the log. However, in terms of programming concepts, it should be Separate exceptions from errors. Exceptions are predictable to users, do not meet expectations, and are controllable structures.

set_exception_handler mentioned above is used to handle exceptions. Usage Consistent with set_error_handler. The exception handling in each framework is very mature. Generally speaking, set_exception_handler will transfer Exception to the framework handleable level, and the framework will also Open good interfaces for users to use, so as to achieve the purpose of user control of exception handling and realize customization and expansion.

Summary

php's error handling mechanism is always ignored, but it is useful for debugging. Monitoring errors plays a great role. This article mainly introduces the main knowledge points and makes a summary. I hope it will be useful to everyone. For more details, please check the manual.

Learning Materials

Predefined constants
Runtime configuration
Error handling function
Summary of PHP's error mechanism
Exceptions
Errors
PHP exception handling
Symfony Debug: is a complete application , it can be said to be a comprehensive tutorial, covering all error-related knowledge points. It is recommended to read the source code.

The above is the detailed content of PHP error handling issues. For more information, please follow other related articles on the PHP Chinese website!