difference between ++i and i++ in for loop

Question

I understand well how postfix and prefix increments/decrements work. But my question is, in a for loop, which is more efficient or faster, and which is more commonly used and why?

Prefix?

for(i = 0; i < 3; ++i) {...}

Or postfix?

for(i = 0; i < 3; i++) {...}

possible duplicate of [Difference between i++ and ++i in a for loop](http://stackoverflow.com/questions/2391141/difference-between-i-and-i-in-a-for-loop) — Michael Petrotta, Sep 25 '11 at 05:39
possible duplicate of [i++ less efficient than ++i, how to show this?](http://stackoverflow.com/questions/1116735/i-less-efficient-than-i-how-to-show-this) — Brian Roach, Sep 25 '11 at 05:39

score 1 · Answer 1 · edited Sep 25 '11 at 05:40

1

For ints in this context there is no difference -- the compiler will emit the same code under most optimization levels (I'd venture to say even in the case of no optimization).

In other contexts, like with C++ class instances, there is some difference.

edited Sep 25 '11 at 05:40

flight

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answered Sep 25 '11 at 05:37

Foo Bah

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Gaijinhunter · Answer 2 · 2011-09-25T05:59:07.517

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Either works, and one is not more efficient or faster than the other in this case. It's common for people to use ++1, maybe because that is what was used in K&R and other influential books.

edited Sep 25 '11 at 05:59

answered Sep 25 '11 at 05:39

Gaijinhunter

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There is no reason that `++i` (especially in a statement context) needs to create any more "local copies" that `i++` does. – Sep 25 '11 at 05:51

score 0 · Accepted Answer · answered Sep 25 '11 at 05:39

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In this particular case, none is actually more efficient than the other. I would expect ++i to be more commonly used, because that's what would be more efficient for other kinds of iterations, like iterator objects.

answered Sep 25 '11 at 05:39

K-ballo

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Why does it only matter when iterator or object are in use? – Unheilig Dec 20 '14 at 13:32

meandbobbymcgee · Answer 4 · 2011-09-25T05:55:54.960

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In my opinion, choosing prefix or postfix in a for loop depends on the language itself. In c++ prefix is more efficient and consistent. Because in the prefix type, compiler does not need to copy of unincremented value. Besides your value must not be an integer, if your value is an object than this prefix type is more powerful.

edited Sep 25 '11 at 05:55

answered Sep 25 '11 at 05:46

meandbobbymcgee

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difference between ++i and i++ in for loop

4 Answers4