i++ less efficient than ++i, how to show this?

Question

I am trying to show by example that the prefix increment is more efficient than the postfix increment.

In theory this makes sense: i++ needs to be able to return the

Answer 1

Try to use while or do something with returned value, e.g.:

#define SOME_BIG_CONSTANT 1000000000

int _tmain(int argc, _TCHAR* argv[])
{
    int i = 1;
    int d = 0;

    DWORD d1 = GetTickCount();
    while(i < SOME_BIG_CONSTANT + 1)
    {
        d += i++;
    }
    DWORD t1 = GetTickCount() - d1;

    printf("%d", d);
    printf("\ni++ > %d <\n", t1);

    i = 0;
    d = 0;

    d1 = GetTickCount();
    while(i < SOME_BIG_CONSTANT)
    {
        d += ++i;

    }
    t1 = GetTickCount() - d1;

    printf("%d", d);
    printf("\n++i > %d <\n", t1);

    return 0;
}

Compiled with VS 2005 using /O2 or /Ox, tried on my desktop and on laptop.

Stably get something around on laptop, on desktop numbers are a bit different (but rate is about the same):

i++ > 8xx < 
++i > 6xx <

xx means that numbers are different e.g. 813 vs 640 - still around 20% speed up.

And one more point - if you replace "d +=" with "d = " you will see nice optimization trick:

i++ > 935 <
++i > 0 <

However, it's quite specific. But after all, I don't see any reasons to change my mind and think there is no difference :)