I've read that I should avoid the postfix increment operator because of performance reasons (in certain cases).
But doesn't this affect code readability? In my opinion:
for(int i = 0; i < 42; i++);
/* i will never equal 42! */
Looks better than:
for(int i = 0; i < 42; ++i);
/* i will never equal 42! */
But this is probably just out of habit. Admittedly, I haven't seen many use ++i.
Is the performance that bad to sacrifice readability, in this case? Or am I just blind, and ++i is more readable than i++?
Best Answer
The facts:
i++ and ++i are equally easy to read. You don't like one because you're not used to it, but there's essentially nothing you can misinterpret it as, so it's no more work to read or write.
In at least some cases, the postfix operator will be less efficient.
However, in 99.99% cases, it won't matter because (a) it'll be acting on a simple or primitive type anyway and it's only a problem if it's copying a big object (b) it won't be in a performance critical part of code (c) you don't know if the compiler will optimise it or not, it may do.
Thus, I suggest using prefix unless you specifically need postfix is a good habit to get into, just because (a) it's a good habit to be precise with other things and (b) once in a blue moon you'll intend to use postfix and get it the wrong way round: if you always write what you mean, that's less likely. There is always a trade-off between performance and optimisation.
You should use you common sense and not micro-optimise until you need to, but neither be flagrantly inefficient for the sake of it. Typically this means: first, rule out any code construction which is unacceptably inefficient even in non-time-critical code (normally something representing a fundamental conceptual error, like passing 500MB objects by value for no reason); and second, of every other way of writing the code, choose the clearest.
However, here, I believe the answer is simple: I believe writing prefix unless you specifically need postfix is (a) very marginally clearer and (b) very marginally more likely to be more efficient, so you should always write that by default, but not worry about it if you forget.
Six months ago, I thought the same as you, that i++ was more natural, but it's purely what you're used to.
EDIT 1: Scott Meyers, in "More Effective C++" who I generally trust on this thing, says you should in general avoid using the postfix operator on user-defined types (because the only sane implementation of the postfix increment function is to make a copy of the object, call the prefix increment function to perform the increment, and return the copy, but copy operations can be expensive).
So, we don't know whether there are any general rules about (a) whether that is true today, (b) whether it also applies (less so) to intrinsic types (c) whether you should be using "++" on anything more than a lightweight iterator class ever. But for all the reasons I described above, it doesn't matter, do what I said before.
EDIT 2: This refers to general practice. If you think it DOES matter in some specific instance, then you should profile it and see. Profiling is easy and cheap and works. Deducing from first principles what needs to be optimized is hard and expensive and doesn't work.