What is the difference between intXX_t and int_fastXX_t?

Question

I have recently discovered existence of standard fastest type, mainly int_fast32_t and int_fast64_t.

I was always told that, for normal use on mainstream archit

Answer 1

There will probably not be a difference except on exotic hardware where int32_t and int16_t don't even exist.

In that case you might use int_least16_t to get the smallest type that can contain 16 bits. Could be important if you want to conserve space.

On the other hand, using int_fast16_t might get you another type, larger than int_least16_t but possibly faster for "typical" integer use. The implementation will have to consider what is faster and what is typical. Perhaps this is obvious for some special purpose hardware?

On most common machines these 16-bit types will all be a typedef for short, and you don't have to bother.