Analysis of error handling and exception handling mechanisms in PHP_PHP tutorial

例：

复制代码 代码如下:

$a = fopen('test.txt','r');
//这里并没有对文件进行判断就打开了，如果文件不存在就会报错
?>

那么正确的写法应该如下：

复制代码 代码如下:

if(file_exists('test.txt')){
$f=fopen('test.txt','r');
//使用完后关闭
fclose($f);
}
?>

一、PHP错误处理的三种方式A、简单的die()语句；
等价于exit();
例：

复制代码 代码如下:

if(!file_exists('aa.txt')){
die('文件不存在');
} else {
//执行操作
}
//如果上面die()被触发，那么这里echo接不被执行
echo 'ok';

简洁写法：

复制代码 代码如下:

file_exits('aaa.txt') or die('文件不存在');
echo 'ok';

B、自定义错误和错误触发器

1、错误处理器（自定义错误，一般用于语法错误处理）
创建自定义错误函数（处理器），该函数必须有能力处理至少两个参数（error_level和errormessage），但是可以接受最多五个参数（error_file、error_line、error_context）
语法：

复制代码 代码如下:

function error_function($error_level,$error_message,$error_file,$error_line,$error_context)
//创建好后还需要改写set_error_handler();函数
set_error_handler('error_function',E_WARNING);//这里error_function对应上面创建的自定义处理器名，第二个参数为使用自定义错误处理器的错误级别；

错误报告级别(了解即可)

这些错误报告级别是错误处理程序旨在处理的错误的不同的类型：

值	常量	描述
2	E_WARNING	非致命的 run-time 错误。不暂停脚本执行。
8	E_NOTICE	Run-time 通知。 脚本发现可能有错误发生，但也可能在脚本正常运行时发生。
256	E_USER_ERROR	致命的用户生成的错误。这类似于程序员使用 PHP 函数 trigger_error() 设置的 E_ERROR。
512	E_USER_WARNING	非致命的用户生成的警告。这类似于程序员使用 PHP 函数 trigger_error() 设置的 E_WARNING。
1024	E_USER_NOTICE	用户生成的通知。这类似于程序员使用 PHP 函数 trigger_error() 设置的 E_NOTICE。
4096	E_RECOVERABLE_ERROR	可捕获的致命错误。类似 E_ERROR，但可被用户定义的处理程序捕获。(参见 set_error_handler())
8191	E_ALL	所有错误和警告，除级别 E_STRICT 以外。 （在 PHP 6.0，E_STRICT 是 E_ALL 的一部分）

2. Error trigger (generally used to handle logical errors)
Requirement: For example, if you want to receive an age, if the number is greater than 120, it is considered an error
Traditional method :

Copy code The code is as follows:

if($age>120){
echo 'Wrong age'; exit();
}

Use trigger:

Copy code The code is as follows:

if($age>120){
//trigger_error('error message'[,'error level']);The error level here is optional and is used to define the level of the error
// User-defined levels include the following three types: E_USER_WARNING, E_USER_ERROR, E_USER_NOTICE
trigger_error('age error');//This is the default error handling method of the calling system, we can also use a custom processor
}
//Custom processor, same as above
function myerror($error_level,$error_message){
echo 'error text';
}
//At the same time, the system default needs to be changed Handling function
set_error_handler('myerror',E_USER_WARNING);//Same as above, the first parameter is the name of the custom function, and the second is the error level [The error levels here are usually the following three: E_USER_WARNING, E_USER_ERROR , E_USER_NOTICE]
//Now you can use the custom error handling function by using trigger_error

Exercise questions:

Copy codeThe code is as follows:

date_default_timezone_set('PRC');
function myerror($error_level,$error_message){
$info= " Error number: $error_leveln";
$info.= "Error message: $error_messagen";
$info.= 'Occurrence time:'.date('Y-m-d H:i:s');
$filename='aa.txt';
if(!$fp=fopen($filename,'a')){
'Failed to create file'.$filename.';
}
if(is_writeable($filename)){
if(!fwrite($fp,$info)){
echo 'Failed to write file';
} else {
echo 'Successful Record error message';
}
fclose($fp);
} else {
echo 'File'.$filename.'not writable';
}
exit() ;
}
set_error_handler('myerror',E_WARNING);
$fp=fopen('aaa.txt','r');
?>

C. Error log
By default, according to the error_log configuration in php.ini, php sends error records to the server's error recording system or file. Error records can be sent to files or remote destinations by using the error_log() function;
Syntax:
error_log(error[,type,destination,headers])
The type part is usually 3, which means it comes after the file Append error information without overwriting the original content
destination represents the destination, that is, the stored file or remote destination
For example: error_log("$error_info",3,"errors.txt");
2. PHP exception handling [Key points]
1. Basic syntax

Copy code The code is as follows:

try{
//Code that may cause errors or exceptions
//catch Exception is a defined exception class in PHP
} catch(Exception $e){
//For exception handling, method:
//1. Handle it yourself
//2. Don’t handle it, throw it again
}

2. The processing handler should include:
Try - use The exception function should be located within a "try" block. If no exception is triggered, the code continues execution as usual. But if an exception is triggered, an exception will be thrown.
Throw - This specifies how to trigger the exception. Each "throw" must correspond to at least one "catch"
Catch - The "catch" code block will catch the exception and create an object containing the exception information
Let us trigger an exception:

Copy code The code is as follows:

//Create a function that can throw an exception
function checkNum($number ){
if($number>1){
throw new Exception("Value must be 1 or below");
}
return true;
}
//in Exceptions are triggered in the "try" code block
try{
checkNum(2);
//If the exception is thrown, the following line of code will not be output
echo 'If you see this , the number is 1 or below';
}catch(Exception $e){
//Catch exception
echo 'Message: ' .$e->getMessage();
}
?>

The above code will get an error similar to this:
Message: Value must be 1 or below
Example explanation:
The above code throws an exception and catches it:
Create checkNum() function. It detects whether the number is greater than 1. If so, throw an exception.
Call the checkNum() function in the "try" code block.
Exception in checkNum() function is thrown
The "catch" code block receives the exception and creates an object ($e) containing the exception information.
By calling $e->getMessage() from this exception object, the error message from the exception is output
However, in order to follow the principle of "each throw must correspond to a catch", you can set a top-level exception processor to handle missed errors.
The set_exception_handler() function can set a user-defined function that handles all uncaught exceptions

Copy the code The code is as follows:

//Set a top exception handler
function myexception($e){
　 echo 'this is top exception';
} //Modify the default exception handler
set_exception_handler("myexception") ;
try{
　$i=5;
　if($i<10){
　throw new exception('$i must greater than 10');
　}
} catch(Exception $e){
　 // Handle exceptions
Echo $e->getMessage().'
';
　 // Do not handle exceptions and continue to throw
Throw new exception('errorinfo'); //You can also use throw $e to retain the original error message;
}

Create a custom exception class

Copy code The code is as follows:

class customException extends Exception{
Public function errorMessage(){
//error message $errorMsg = ' Error on line '.$this->getLine().' in '.$this->getFile().': '.$this->getMessage().' is not a valid E-Mail address'; return $errorMsg;
　}
}
//Use
try{
　throw new customException('error message');
} catch(customException $e){
　echo $e->errorMsg();
}

You can use multiple catches to return error messages in different situations

Copy code The code is as follows:

try{
　$i=5;
　if($i>0){
Throw new customException('error message');//Use custom exception class processing
} if($i<-10){
throw new exception('error2');//Use system default Exception handling
　}
}catch(customException $e){
echo $e->getMessage();
}catch(Exception $e1){
echo $e1-> getMessage();
}

Exception rules
Code that requires exception handling should be placed in a try code block to catch potential exceptions. Each try or throw block must have at least one corresponding catch block. Use multiple catch blocks to catch different kinds of exceptions. Exceptions can be re-thrown in a catch block within the try code. In short: if an exception is thrown, you must catch it.

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