in a "for" loop, is the Terminating Condition Re-Evaluated on Each Iteration?

Question

Possible Duplicates:
for loop optimization
for-loop optimization - needed or not?

e.g.

  int maxloop = complicated();
   for (int i=0;i<maxloop;i++){}

or

 for (int i=0;i<complicated();i++){}

Is the compiler smart enough to optimize it?

what about while?

@CodeNaked That is Java, there is no guarantee that C# works the same way — Oskar Kjellin, Jul 26 '11 at 23:30
This must not be optimised as you expect! So, yes, compiler is smart enough... to know it have to be kept as it. — Al Kepp, Jul 26 '11 at 23:40
@Oskar - You're right. Then it's probably this one http://stackoverflow.com/questions/4477296/for-loop-optimization-needed-or-not — CodeNaked, Jul 26 '11 at 23:54

score 2 · Accepted Answer · answered Jul 26 '11 at 23:02

2

No, the compiler is not smart enough to optimize it because it cannot guarantee that complicated() doesn't do anything different if it is run multiple times.

answered Jul 26 '11 at 23:02

StriplingWarrior

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score 1 · Answer 2 · answered Jul 26 '11 at 23:03

1

Actually you need to assign the output to a variable to avoid the recalculation overhead. Compiler doesn't do this because you may have an aim in putting a method return value as the limit (i.e. you may need to recalculate the limit after each iteration). To test this, just put Thread.Sleep(5000); in the compilcated() method and you'll see the wait time.

answered Jul 26 '11 at 23:03

Teoman Soygul

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Or just but a breakpoint in the `complicated()` method and see it happen – Oskar Kjellin Jul 26 '11 at 23:34
Oh yes, simply `Debugger.Break();` – Teoman Soygul Jul 26 '11 at 23:36
Or a simple console app test would include a `Console.WriteLine("The complicated method wrote this line");` – Oskar Kjellin Jul 26 '11 at 23:38

score 0 · Answer 3 · answered Jul 26 '11 at 23:02

0

No, it isn't, as complicated could be a method depending on other complex methods or result in different behaviour after each iteration.

answered Jul 26 '11 at 23:02

Femaref

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score 0 · Answer 4 · answered Jul 26 '11 at 23:03

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The compiler cannot optimize it because there are situations in which "complicated()" will not return the same integer every time. Therefore, the condition is executed every time. Your first snippet of code is must more efficient.

answered Jul 26 '11 at 23:03

Chris

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in a "for" loop, is the Terminating Condition Re-Evaluated on Each Iteration?

4 Answers4