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I read somewhere that the switch statement uses "Binary Search" or some sorting techniques to exactly choose the correct case and this increases its performance compared to else-if ladder.

And also if we give the case in order does the switch work faster? is it so? Can you add your valuable suggestions on this?

We discussed here about the same and planned to post as a question.

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  • Depends on the compiler and the actual switch cases. Some common implementations are demonstrated in Secrets of Reverse Engineering. Commented Dec 28, 2012 at 9:48
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    Duplicate of: stackoverflow.com/questions/2596320/… Commented Dec 28, 2012 at 9:53
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    My personal experience with GCC is limited, and I can only point to one interesting example. Edit: of course, if you're curious, you should compile multiple different switch() statements and disassemble the results. Commented Dec 28, 2012 at 9:54
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    @DCoder codeproject.com/Articles/100473/… Commented Dec 28, 2012 at 10:02
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    That is a nice article, but again - the compiler is free to implement a switch however it wants - as a series of if/else, as a one-level or multi-level jump table, as a binary search pattern... the fact that MSVC implements them in a particular way does not guarantee that GCC, clang or ICC will do the same. Commented Dec 28, 2012 at 10:04

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It's actually up to the compiler how a switch statement is realized in code.

However, my understanding is that when it's suitable (that is, relatively dense cases), a jump table is used.

That would mean that something like:

switch(i) { case 0: doZero(); break; case 1: doOne(); case 2: doTwo(); break; default: doDefault(); }

Would end up getting compiled to something like (horrible pseudo-assembler, but it should be clear, I hope).

load i into REG compare REG to 2 if greater, jmp to DEFAULT compare REG to 0 if less jmp to DEFAULT jmp to table[REG] data table ZERO ONE TWO end data ZERO: call doZero jmp END ONE: call doOne TWO: call doTwo jmp END DEFAULT: call doDefault END:

If that's not the case, there are other possible implementations that allow for some extent of "better than a a sequence of conditionals".

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The “use value as offset jump destination” trick doesn’t work for cases like switch( i ) { case 0: foo(); case 9999999: bar(); } otherwise it would massively add to the compiled program size.
Yes, other possible implementations would be "a hash table of target addresses", "a few jump tables, with a bunch of if/then/else to get to the right table", etc. The exact form would depend on the exact code.
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How swtich is implemented depends on what values you have. For values that are close in range, the compiler will generally generate a jump table. If the values are far apart, it will generate a linked branch, using something like a binary search to find the right value.

The order of the switch statements as such doesn't matter, it will do the same thing whether you have the order in ascending, descending or random order - do what makes most sense with regard to what you want to do.

If nothing else, switch is usually a lot easier to read than an if-else sequence.

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I think you've captured the main point - a compiler doesn't have to be consistent about the code it emits for a switch statement, it can choose a strategy based on your actual conditions.
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On some googling I found some interestin link and planned to post as an answer to my question. http://www.codeproject.com/Articles/100473/Something-You-May-Not-Know-About-the-Switch-Statem

Comments are welcome..

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Yes, that's sort of what I tried to say - the compiler will build tables and use them to jump through. But it may also use compare/jump statements, and it will hybridize between the two if that leads to "better" code [all depending on what you define as better - someone may think that having 32KB of table to sort out a switch-statement is better than four jumps, because those jumps are bad to predict in the branch prediction in the processor, but someone else thinks it's ridiculous to have 32KB to solve this particular case]
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Although it can be implemented as several ways it depends on how the language designer wants to implement it. One possible efficient way is to use Hash Maps Map every condition (usually integer) to the corresponding expression to be evaluated followed by a jump statement. Other solutions also might work as often switch has finite conditions but a efficient solution shall be to use Hash map

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