Menu
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.
763
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.
The body of a switch statement is known as a switch block. A statement in the switch block can be labeled with one or more case or default labels. The switch statement evaluates its expression, then executes all statements that follow the matching case label.
Switch Case Example in CA switch construct is used to compare the value stored in variable num and execute the block of statements associated with the matched case. In this program, since the value stored in variable num is eight, a switch will execute the case whose case-label is 8.
The switch-case construct is pretty similar to an if-else statement, you can use the OR operator in an if however.
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".
140
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.
36
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..
41
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
