Question

I do not understand why this is the case:

Printf.sprintf "%08s" "s" = Printf.sprintf "%8s" "s"
- : bool = true

In other words, I would expect:

Printf.sprintf "%08s" "s"
- : string = "0000000s"

and not the actual result:

- : string = "       s"

could someone please clarify why this is so?

Answer 1

From the documentation of printf, you can see that the 0 flag does not apply to %s.

0: for numerical conversions, pad with zeroes instead of spaces.

(Emphasis is mine.)

Notice that, in C, it leads to an undefined behavior.