[xamuel]

You meant to say, "if you're passing a pointer to an array to a function, the function doesn't know the size of the array unless you pass that as another argument".

When passing a (pointer to a) data structure to a function, in 99.99% of cases there's only one data structure you'd pass, and you build this into the function's prototype, e.g.,

  int myfunction( struct my_structure *x )

instead of

  int myfunction( void *x )

and so, yes, the function does know the size of the structure. And in the case of arrays, often it's enough to mark the end of the array (with '\0' in the case of char arrays or NULL in the case of pointer arrays), I'd only roll my sleeves up and worry about minimizing length calculations if I had actually done some profiling and determined that such nitty-gritty optimization was needed (it rarely is).