Is there a performance difference between i++ and ++i in C?

Question

Is there a performance difference between i++ and ++i if the resulting value is not used?

Answer 1

Here's an additional observation if you're worried about micro optimisation. Decrementing loops can 'possibly' be more efficient than incrementing loops (depending on instruction set architecture e.g. ARM), given:

for (i = 0; i < 100; i++)

On each loop you you will have one instruction each for:

1. Adding 1 to i.
2. Compare whether i is less than a 100.
3. A conditional branch if i is less than a 100.

Whereas a decrementing loop:

for (i = 100; i != 0; i--)

The loop will have an instruction for each of:

1. Decrement i, setting the CPU register status flag.
2. A conditional branch depending on CPU register status (Z==0).

Of course this works only when decrementing to zero!

Remembered from the ARM System Developer's Guide.