哪个更快更好，Switch Case还是其他如果？ [英] Which is Faster and better, Switch Case or if else if?

问题描述

哪种方法更好更快：if或switch？

Which is the better and fastest methods : if or switch ?

if(x==1){
  echo "hi";
} else if (x==2){
  echo "bye";
}

switch(x){
  case 1
    ...
  break;
  default;
} 

推荐答案

你的第一个例子是完全错误的。您需要 elseif 而不是 else 。

Your first example is simply wrong. You need elseif instead of just else.

如果你使用 if..elseif ... 或 switch 主要是偏好问题。性能是相同的。

If you use if..elseif... or switch is mainly a matter of preference. The performance is the same.

但是，如果您的所有条件都是 x == value 类型 x 在各种条件下都相同， switch 通常都有意义。我还只使用开关如果超过例如两个条件。

However, if all your conditions are of the type x == value with x being the same in every condition, switch usually makes sense. I'd also only use switch if there are more than e.g. two conditions.

如果变量部分是函数调用， switch 实际上给你带来性能优势的情况：

A case where switch actually gives you a performance advantage is if the variable part is a function call:

switch(some_func()) {
    case 1: ... break;
    case 2: ... break;
}

然后 some_func（）仅用

if(some_func() == 1) {}
elseif(some_func() == 2) {}

它将被调用两次 - 包括函数的可能副作用打电话发生两次。但是，您总是可以使用 $ res = some_func（）; 然后在<$ c $中使用 $ res c>如果条件 - 所以你可以完全避免这个问题。

it would be called twice - including possible side-effects of the function call happening twice. However, you could always use $res = some_func(); and then use $res in your if conditions - so you can avoid this problem alltogether.

你不能使用switch的情况一切都是因为你有更复杂的条件 - 开关仅适用于 x == y y 是一个常数值。

A case where you cannot use switch at all is when you have more complex conditions - switch only works for x == y with y being a constant value.

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