Usage of 'short' in C++

Question

Why is it that for any numeric input we prefer an int rather than short, even if the input is of very few integers.

The size of short is 2 bytes on my x86 and 4 bytes for int, shouldn't it be better and faster to allocate than an int?

Or I am wrong in saying that short is not used?

Answer 1

CPUs are usually fastest when dealing with their "native" integer size. So even though a short may be smaller than an int, the int is probably closer to the native size of a register in your CPU, and therefore is likely to be the most efficient of the two.

In a typical 32-bit CPU architecture, to load a 32-bit value requires one bus cycle to load all the bits. Loading a 16-bit value requires one bus cycle to load the bits, plus throwing half of them away (this operation may still happen within one bus cycle).

Answer 2

A 16-bit short makes sense if you're keeping so many in memory (in a large array, for example) that the 50% reduction in size adds up to an appreciable reduction in memory overhead. They are not faster than 32-bit integers on modern processors, as Greg correctly pointed out.