Which is Faster and better, Switch Case or if else if?

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;
}
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最佳答案

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

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

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.

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;
}

Then some_func() is only called once while with

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

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.

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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It's depending on usage. If you have fxp status (online, away, dnd, offline...) its better use switch.

switch(status)
{
case 'online':
...
}

But if you wanna something like this

if ((last_reply.ContainsKey(name)) && (last_reply[name] < little_ago))

or 

if (msg.ToString()[0] == '!')

its better use if else.

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I belive the compiler will turn them into very similar, or maybe even identical code at the end of the day.

Unless you're doing something weird, don't try and do the optimisation for the compiler.

Also, developer time is generally more important than runtime (with the exception of games), so it'sbbetter to make its more readable and maintainable.

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in my opinion the "if/else" is faster but not better than switch but i prefer this:

echo ($x==1?"hi":($x==2?"bye":""));

if you have to do 1,2 cases like if/else if/else

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General rule is use switch whenever the number of conditions is greater than 3 (for readability).

if / else if / else is more flexible (hence better), but switch is slightly faster because it just computes the condition once and then checks for the output, while if has to do this every time.

EDIT: Seems like ABC0 is slower than if after all, I could swear this was not the case...

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According to phpbench.com, if/elseif is slightly faster, especially when using strict comparison (===).

enter image description here

But it'll only really matter if you want to shave off microseconds on a function that'll be called thousands of times.

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When using ==, performance of if ... elseif compared to switch is almost identically. However, when using ===, if ... elseif is about 3 times faster (according to: phpbench).

Generally, you should go with what is most readable and use switch when making more than 3 comparisons. If performance is a major concern and you don't need to make any type conversions, then use if ... elseif with ===.

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I found this post: https://gist.github.com/Jeff-Russ/2105d1a9e97a099ca1509de1392cd314 which indicates switch/case to be faster than if/elseif with ===.

They also indicate nested if statements which makes a lot more sense and also provide far better results.

Their times:

nested if/elseif === : 0.25623297691345 (NESTED IF)

switch/case : 0.33157801628113 (SWITCH CASE)

if/elseif with === : 0.45587396621704 (FLAT IF)

only if with === : 0.45587396621704 (ONLY IF)

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Switch is faster than if because switch uses jump table and jump table is made by compiler during compile time and run by cpu/os. For ex if you have 100 cases and you will get your value in 100 th one so what do you think it will run all 99 conditions...no..it will directly jump to 100th one with the help of jump table..so how can we prove this?...if you write default statement at start and then run the program will you get default value,since it is at start? No..you will get your desired answer because of jump table..it knows where is default and where is your assigned value and it will directly take you to your desired answer.. Talking about which is better... Every work that can be done in if can be done in switch.. But for lesser condition if is better and for more conditions switch..like upto 3 conditions if is good.. after that a good programmer uses switch..that's all


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