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关于赋值和判断语句的问题

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Jun 23, 2016 pm 02:15 PM

 if ($userName=="system"){    $userName_msg="自动"; }else{   $userName_msg=""; }

和

 $userName_msg=""; if($userName=="system"){    $userName_msg="自动"; }

我想要给变量$userName_msg 赋值，上边两种写法有什么差别吗？

回复讨论(解决方案)

实现没有差别。
但从代码质量看，当然是第二种好了。
这种只有两种情况的判断，当然还是三目运算好了

实际上没有差别。

只不过从使用变量之前都首先要初始化的概念上来说，肯定是第二种更加符合使用前首先初始化。

而第一种给人的感觉是根据不同的逻辑，而用不同的值去初始化同一个变量，将初始化和逻辑结合的太紧密了。

实现没有差别。
但从代码质量看，当然是第二种好了。
这种只有两种情况的判断，当然还是三目运算好了
++

楼上的都说了

第一种，不论条件成立与否，内存分配一次
第二种，在条件成立时内存分配两次，第一次分配舍弃了进入垃圾回收

第一种，和三目运算能确保变量存在并有值
第二种，若赋初值和赋新值的代码分开太远，就不能保证赋初值一定存在了。极有可能导致访问不存在的变量

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