Why does n++ execute faster than n=n+1?
In C language, Why does n++ execute faster than n=n+1?
(int n=...; n++;)
(int n=...; n=n+1;)
Our instructor asked that question in today's class. (this is not homework)
Answer
That would be true if you are working on a "stone-age" compiler...
In case of "stone-age":
++n is faster than n++ is faster than n=n+1
Machine usually have increment x as well as add const to x
- In case of
n++, you will have 2 memory access only (read n, inc n, write n ) - In case of
n=n+1, you will have 3 memory access (read n, read const, add n and const, write n)
But today's compiler will automatically convert n=n+1 to ++n, and it will do more than you may imagine!!
Also on today's out-of-order processors -despite the case of "stone-age" compiler- runtime may not be affected at all in many cases!!