How "i++" is more efficient than "i = i + 1"?

Question

Is there is any difference between these two statements performance wise ?

i++;
i = i + 1;

++i is most efficient, i++ returns a copy of i before incrementing the variable. Were ++i simple increments the variable and avoids the copy. — Anthony Raimondo, Aug 29 '14 at 05:06

score 7 · Accepted Answer · answered Aug 29 '14 at 05:02

Depends on the optimisation. i++ can, on most processors, be represented as a single machine language instruction. i = i + 1, on the other hand, could be represented by up to four: load i, load 1, add, store to i; although, even a middling smart compiler should be able to recognise it can rewrite it into the former.

score 0 · Answer 2 · answered Aug 29 '14 at 05:01

0

no, there is no difference. The compiler will compile these into the same assembly

answered Aug 29 '14 at 05:01

Stephen

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Yes, Amadan's answer is more complete and correct. I did assume that the code was compiled with optimization enabled. – Stephen Aug 29 '14 at 05:10
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@DividebyZero: Well, to be honest, today in the age of LLVM and stuff, there actually is no difference, I believe. It's just that I don't automatically assume C = modern C :) (I have some acquaintances who still work on 25-year-old Sun boxen) – Amadan Aug 29 '14 at 05:14

How "i++" is more efficient than "i = i + 1"?

2 Answers2