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PHP错误详解

Jun 13, 2016 pm 01:23 PM
exceptionfunctionnbspphp

PHP异常详解

PHP的异常是什么?

PHP 5 提供了一种新的面向对象的错误处理方法。异常处理用于在指定的错误(异常)情况发生时改变脚本的正常流程。这种情况称为异常。

 

一般使用方法:

<?php
function test() {
	throw new Exception("异常啦");
}
try {
     test();
} catch (Exception $e) {
 echo $e->getMessage();
}
  1. throw new Exception('XXX') : 抛出一个异常
  2. try  : 使用异常的函数应该位于 "try" 代码块内。如果没有触发异常,则代码将照常继续执行。但是如果异常被触发,会抛出一个异常。
  3. Catch:代码块会捕获异常,并创建一个包含异常信息的对象

自定义异常类:

class myException extends Exception {
 public function errorMessage() {
  	$errorMsg = 'Error on line '.$this->getLine().' in '.$this->getFile()
  .': <b>'.$this->getMessage().'</b> is not a valid E-Mail address';
  	return $errorMsg;
  }
}


try {
  throw new myException($email);
}catch (myException $e){
 echo $e->errorMessage();
}
  1. myException类是一个自定义的异常类,必须继承Exception
  2. Exception是一个PHP自带的内置的异常类,默认情况下会使用PHP默认的内置异常类,但是我们可以通过自定义的方式,自定义成满足自己需求的异常类。
  3. 使用自定义异常类的时候,throw new myException 抛出异常也需要抛出自定义的异常类类名
  4. catch的时候也需要捕获自定义的异常类
  5. 如果抛出了异常而不捕获处理的话,就会发生PHP代码报错,如下:
Fatal error: Uncaught exception 'myException' in D:\AppServ\www\cctv\trunk\index.php:12 Stack trace: #0 {main} 
thrown in D:\AppServ\www\cctv\trunk\index.php on line 12


PHP默认异常类详细:

class exception
{
    protected $message = 'Unknow exception'; //自定义的异常信息
    protected $code = 0; //定义的异常代码
    protected $file; //发生异常的PHP程序名
    protected $line; //发生异常的PHP行号
    //用于传递用户自定义异常信息和用户自定义异常代码的构造函数
    function __construct($message=null,$code=0);
    final function getMessage();
    final function getCode();
    final function getFile();
    final function getLine();
    final function getTrace(); //以数组形式返回异常传递的路线
    final function getTraceAsString(); //返回格式化成字符串的getTrace函数信息
    function __toString(); //可重载,用于返回可输出的字符串
}
  1. 可以看到PHP默认异常类中有很多自定义变量和方法
  2. $e->getMessage 一般是获取错误信息
  3. $e->getCode() 一般是获取错误码
  4. $e->getFile() 获取错误的文件信息
  5. $e->getLine() 获取错误行数
  6. $e->getTrace() 异常经过的文件路径
  7. __toString() 一般可以重载,用于返回可输出的字符串

PHP异常类的作用:

  1. 捕获异常,一般可以在MYSQL链接不上,或者业务逻辑错误的时候,抛出异常,在代码最顶端接收。
  2. 异常分析处理。可以在出异常的时候,捕获到异常的错误信息,写入日志。
  3. 可以返回友好化的提示信息,例如WEB端可以返回页面形式,也可以在AJAX端返回JSON数据格式。
  4. 原则:如果异常抛出了,就必须捕获它,否则会PHP报错。
     


 

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