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背景：对于书上一些连接mysql的例子，总是像写c语言一样，一行一行的，直接写下去，确实好看明白，但是在实际使用中，如果暴露出错误到前端页面是不太好的，这时候需要try catch来捕获这些错误，对于mysql的连接句柄的密码是否正确可以用if直接判断其返回值，再用throw new exception("Sorry,could not connect to mysql.");而对于一些非密码的网络及数据库，得用上catch，网上有一篇文章就有这样的类似介绍。

<?php   class OperateDB   {      private $host='localhost';      private $userName='root';      private $passwd='';              //连接数据库     public  function OpenDB()     {       try       {         if($db=mysql_connect( $host,$userName,$passwd))         {           //$db=mysql_connect($host,$username,$passwd);           return $db;         }         else         {           throw new exception("Sorry,could not connect to mysql.");         }       }       catch(exception $e)       {         echo $e->getmessage();       }     }     //选择数据库     public function SelectDB($whichdb,$db)     {       try       {                  if(!mysql_select_db($whichdb,$db))         {           throw new exception("Sorry,database could not be opened.");         }                }       catch(exception $e)       {         echo $e->getmessage();       }            }     public function CloseDB($db)     {       mysql_close($db);     }          public function Query($queryString)     {       if($mysquery=mysql_query("$queryString"))       {         return $mysquery;       }       else       {         echo mysql_error();       }     }   } ?>

自己简单实践如下，如果密码错误则会捕获并报如下信息，而不是直接抛出：
一）来个设置温度是否成功了，并无从db查询的数据返回的：
<?php set_time_limit(5) ; Error_reporting(0);             $user = "root"; //数据库用户名 $password = "";//数据库密码 $db_name = "temperature";//数据库 $arrRet = array("opt"=>"setTemperatureValue","status"=>1);//设置温度成功 try {         if($link = mysql_connect("localhost:3306",$user,$password)){             mysql_select_db("$db_name",$link);         }else{             //throw new exception("Sorry,could not connect to mysql.");             $arrRet = array("opt"=>"setTemperatureValue","status"=>-1,"errMsg"=>"Sorry,could not connect to mysql.");//连接数据库失败         } }catch (Exception $e){         $arrRet = array("opt"=>"setTemperatureValue","status"=>-1,"errMsg"=>$e->getMessage());//数据库异常 } $settingTempValue = $_GET["setTemperatureValue"];//设置温度值 $updatedTimes = strtotime(date("Y-m-d H:i:s")); if($_GET['equipNum']=='One'){     $settingTempOption = "settingTempOneValue";//设置温度键值 }else{     $settingTempOption = "settingTempTwoValue";//设置温度键值 } try {     $sql = "replace into   tempoptsetting (settingName,settingValue,updatedTimes) values (\"{$settingTempOption}\",\"{$settingTempValue}\",\"$updatedTimes\")";     $result=mysql_query($sql,$link); } catch (Exception $e) {     $arrRet = array("opt"=>"setTemperatureValue","status"=>-1,"errMsg"=>$e->getMessage());//设置温度失败 } echo json_encode($arrRet); ?>
密码错会报如下错，前端用json去解析判断并提示用户即可，自己也好查错不是：
{"opt":"setTemperatureValue","status":-1,"errMsg":"Sorry,could not connect to mysql."}

二）来个有数据查询并返回的简单示例：
<?php set_time_limit(5) ; Error_reporting(0); $user = "root"; //数据库用户名 $password = "";//数据库密码 $db_name = "temperature";//数据库名 try {     if($link = mysql_connect("localhost:3306",$user,$password)){         mysql_select_db("$db_name",$link);     }else{         //throw new exception("Sorry,could not connect to mysql.");         $equipTempArr = array("opt"=>"getTemperatureValue","status"=>-1,"errMsg"=>"Sorry,could not connect to mysql.");//连接数据库失败         die(json_encode($equipTempArr));     } }catch (Exception $e){         $equipTempArr = array("opt"=>"getTemperatureValue","status"=>-1,"errMsg"=>$e->getMessage());//数据库异常 } //取最后插入的温度值 try {     $sql = "select * from temperatureone where id=(select id from temperatureone order by id desc limit 1) order by id desc  limit 1";     $result=mysql_query($sql,$link);     $curTempOne=mysql_fetch_array($result);     $sql = "select * from temperaturetwo where id=(select id from temperaturetwo order by id desc limit 1) order by id desc  limit 1";     $result=mysql_query($sql,$link);     $curTempTwo=mysql_fetch_array($result);     try{         if(isset($_GET['init'])&&$_GET['init'] == 1){//第一次请求顺带把设置温度也查询出来             $sql = "select * from tempoptsetting where settingName = \"settingTempOneValue\"  limit 1";             $result=mysql_query($sql,$link);             $curTempSetOne = mysql_fetch_array($result);             $sql = "select * from tempoptsetting where settingName = \"settingTempTwoValue\"  limit 1";                     $result = mysql_query($sql,$link);             $curTempSetTwo = mysql_fetch_array($result);             if(($curTempSetOne != NULL) && ($curTempSetTwo != NULL))             $equipTempArr = array("opt"=>"getTemperatureValue","status"=>-1,"curTempOne"=>$curTempOne['nowTempValue'],"curTempTwo"=>$curTempTwo['nowTempValue'],"curTempSetOne" => $curTempSetOne['settingValue'],"curTempSetTwo" => $curTempSetTwo['settingValue']);         }else{             if(($curTempOne != NULL) && ($curTempTwo != NULL))//不为NUll             $equipTempArr = array("opt"=>"getTemperatureValue","status"=>-1,"curTempOne"=>$curTempOne['nowTempValue'],"curTempTwo"=>$curTempTwo['nowTempValue']);         }     }catch (Exception $e) {             $equipTempArr = array("opt"=>"getTemperatureValue","status"=>-1,"errMsg"=>$e->getMessage());//查询数据时异常     } } catch (Exception $e) {     $equipTempArr = array("opt"=>"getTemperatureValue","status"=>-1,"errMsg"=>$e->getMessage());//查询数据时异常 } $equipTempArr2Json = json_encode($equipTempArr); echo $equipTempArr2Json;//打印出现在温度值 ?>
（1）错误结果：
{"opt":"getTemperatureValue","status":-1,"errMsg":"Sorry,could not connect to mysql."}
（2）正确结果：
{"opt":"getTemperatureValue","status":-1,"curTempOne":"40.2","curTempTwo":"38.6","curTempSetOne":"35.5","curTempSetTwo":"55.4"}
原始代码参考来源：http://bbs.csdn.net/topics/240078038

作者：jackxiang@向东博客 专注WEB应用 构架之美 --- 构架之美，在于尽态极妍 | 应用之美，在于药到病除
地址：https://jackxiang.com/post/8059/
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