切换vs if语句 [英] Switch vs if statements

问题描述

我处于两难境地。哪个最好用，为什么..切换或如果？

I'm in a dilemma. Which is best to use and why.. switch or if?

switch ($x) 
{
case 1:
  //mysql query 
  //echo something
  break;
case 2:
  //mysql query 
  //echo something
  break;
}

...

if ($x == 1) {
    //mysql query 
    //echo something    
} 

if ($x == 2) {   
    //mysql query 
    //echo something
}  

推荐答案

它们有不同的含义。

第一个例子将在满足条件时停止。

The first example will stop when the condition is met.

第二个将测试 $ x 两次。

你可能想要第二个，如果一个，如果。这意味着只要一个条件评估为 true ，就会跳过该块。

You may want to make your second if an else if. This will mean the block will be skipped as soon as one condition evaluates to true.

但是如果你想知道哪一个最快，那么你应该考虑哪一个最有效地传达我想要做的事情。它们最有可能最终成为目标架构中的条件跳转。

But if you are wondering which one is fastest, you should instead think which one most effectively communicates what I want to do. They will both most probably end up as conditional jumps in the target architecture.

过早优化......（你知道其余的：P）

Premature optimisation... (you know the rest :P )

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