A look at PHP's exception and error handling

Exceptions and Errors

Example:

  $num = 0;
    try {
        echo 1/$num;
    } catch (Exception $e){
        echo $e->getMessage();//并不能执行到这里
    }
    //说明try{}catch{}是用于捕获异常的，而错误是不能捕获到的。
 
    //手动抛出异常进行捕获
    $num = 0;
    try {
        if($num == 0){
            //通过if判断可以处理错误，手动抛出异常（如何实现自动捕获错误呢，需结合三个php内置函数）
            throw new Exception('除数为零');
        }
        echo 1/$num;
    } catch (Exception $e){
        echo $e->getMessage();
    }

What is Exception

It is allowed to happen when an unexpected situation occurs during the running of the program (you don’t want it to have an abnormal situation), but it is an abnormal situation, according to our normal logic Errors that should not occur but still occur are errors in logic and business processes, not compilation or syntax errors.

What is an error

It is a problem of the php script itself. Most of the cases are caused by wrong syntax and server environment, which makes the compiler Failure to pass inspection or even failure to operate. Warning and notice are both errors, but their levels are different, and errors cannot be captured by try-catch

Classification of errors

Fatal Error: Fatal error (script terminated)

E_ERROR // Fatal running error, the error cannot be recovered, and the execution of the script is suspended

E_CORE_ERROR // During the initialization process when PHP starts Fatal error

E_COMPILE_ERROR // Fatal error at compile time, as if an E_ERROR was generated by the Zend script engine

E_USER_ERROR // Custom error message. Like using the PHP function trigger_error (the error type is set to: E_USER_ERROR)

Parse Error: Compilation time parsing error, syntax error (script terminates running)

E_PARSE // Compilation time syntax parsing error

Warning Error: Warning error (only prompt information is given, the script does not terminate the operation)

E_WARNING // Runtime warning (non-fatal error).

E_CORE_WARNING // Warning (non-fatal error) that occurred during PHP initialization startup.

E_COMPILE_WARNING //Compilation warning

E_USER_WARNING //Warning message generated by the user

Notice Error: Notification error (only notification information is given, the script does not terminate running)

E_NOTICE // Runtime notification. Indicates that the script encounters a situation that may appear as an error.

E_USER_NOTICE // Notification information generated by the user.

5 class generates ERROR level errors, which directly cause the PHP program to exit. They are ERROR = E_ERROR | e){} To catch exceptions, you need to use three functions to catch errors

// 注册一个会在php中止时执行的函数
    register_shutdown_function('myShutdownFunction');
    function myShutdownFunction()
    {
        if ($error = error_get_last()) {
            var_dump(&#39;<b>register_shutdown_function: Type:&#39; . $error[&#39;type&#39;] . &#39; Msg: &#39; . $error[&#39;message&#39;] . &#39; in &#39; . $error[&#39;file&#39;] . &#39; on line &#39; . $error[&#39;line&#39;] . &#39;</b>&#39;);
        }
    }

//注册异常处理函数, 没有捕获处理的异常，将统一再这里处理
    set_exception_handler('myException');
    function myException($exception)
    {
        var_dump("<b>set_exception_handler: Exception: " . $exception->getMessage()  . &#39;</b>&#39;);
    }

 //注册错误处理函数
    set_error_handler('myError');
    function myError($type, $message, $file, $line)
    {
        //var_dump(&#39;<b>set_error_handler: &#39; . $type . &#39;:&#39; . $message . &#39; in &#39; . $file . &#39; on &#39; . $line . &#39; line .</b><br />&#39;);
        throw new Exception($message);
    }

The principle of capturing all errors

It can be seen from set_error_handler () that it can capture some errors, but cannot capture system-level E_ERROR, E_PARSE and other errors, but this part can be captured by register_shutdown_function (). Therefore, the combination of the two can produce very good functions.

Summary

Three functions to automatically capture exceptions and errors

set_error_handler () can only capture part of Error

register_shutdown_function () combined with set_error_handler () function can catch all errors

set_exception_handler () is used to catch exceptions

error_get_last () and finally terminates the error message

In the function that captures the error, manually throw the exception, that is, implement set_exception_handler to capture the error.

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