Re: size_t best practice

Michael S <already5chosen@yahoo.com> writes:

On Sun, 18 Aug 2024 15:23:58 -0700
Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
>

Michael S <already5chosen@yahoo.com> writes:
>

On 18 Aug 2024 12:17:36 GMT
ram@zedat.fu-berlin.de (Stefan Ram) wrote:
>

Mark Summerfield <mark@qtrac.eu> wrote or quoted:
>

So is it considered best practice to use int, long, long long, or
size_t, in situations like these?

>
  In *cough*C++*cough* you could whip up a "SafeSize" class with
  a bulletproof "operator--", so you don't space on the check.
  You could still keep cranking out your code in what's basically C
and just cherry-pick this one gnarly feature from that other
language.
>
SafeSize& operator--()
{ if( value == 0 )
  { throw std::underflow_error("SafeSize decrement underflow"); }
  --value;
  return *this; }

>
But that's not a desired behavior for people that want to write
downcounting for() loops in intuitive manner.

>
Kind of a funny use of the word intuitive, for two reasons.
>
The first is that writing for() loops, especially C for() loops,
is learned behavior.  There can be patterns that one is used to,
but they are not "intuitive" in the usual sense of the word.
>
The second is that people who program in C are accustomed to the
idea of an asymmetry between counting up and counting down,
because of how pointers work.  It's okay to increment a pointer
to one past the end of an array;  it is not okay to decrement a
pointer to one before the beginning of an array.  Because of that
the patterns for going forward and for going backward are just
different.  It seems odd to use the word "intuitive" to recognize
that distinction.

>
I would think that very large part of 'C' programmers ignores this
asymmetry.  They are helped by the fact that 100% of production 'C'
compilers ignore it as well, which means that in practice code that
compares &arr[0] with &arr[-1] works as naively expected on all targets
that have flat memory model and far more often than not works on more
tricky targets as well.

I long ago internalized the rule that C allows pointing one past the
end of an array but does not allow pointing before the beginning.
Certainly I don't expect that all C programmers respect that rule,
but I do expect that most experienced C programmers will, especially
given recent trends in aggressive optimizing, since the consequences
of not doing so can be so dire.

I also long ago developed the habit of not thinking about, at least
most of the time, what is going on "under the hood" when compiling.
A compiler is allowed to take advantage of how pointer arithmetic
works, precisely because the compiler has privileged access to
inside information.  (It occurs to me now that this attitude might
be humorously stated: Thinking "under the hood" Considered Harmful.)

I don't think of either of those traits as ubiquitous, but I also
don't think of them as special or unusual.  Maybe that assumption
isn't as generally apt as I think it is.

Which is not to say I disagree with what you are saying.  Actually
I guess I'd have to say I'm not sure what it is you are saying.
To my way of thinking the function above doesn't change the way I
would write down-counting loops.  It might be useful as a debugging
aid aide, but nothing more (and an assert() is probably better).
I think though that what you're saying is something else but I'm
not sure what it is.

>
Nothing fancy.  Just an ability to write downcounting loops in a
way that I, obviously mistakenly, consider intuitive.
for (i = len-1; i >= 0; --i)

I wouldn't say mistaken just because you used what might be a funny
word choice (and not everyone would agree on that point).  For
example if you had used the phrase "in a natural way" I think most
people would have understood it as you meant for the original.  I'm
just fussy about words.

In many cases, or maybe even most cases, when there is a down
counting loop the code looks cleaner (to be clear, to me) to start
after the end than at the end.  For example, the inner loop of an
insertion sort:

   T e = elements[i];
   for(  j = i;  j > 0  &&  before( e, elements[j-1] );  j--  ){
        elements[j] = elements[j-1];
   }
   elements[j] = e;

The invariant is that j is the index of a "hole" that moves down
the array.

Again, my reaction doesn't mean that your way is wrong, or even bad.
People get used to what they get used to.  Maybe this relates to our
attitudes about index signedness:  I strongly prefer unsigned types
for indexing, and you prefer, I think, signed types.  Sometimes
people prefer one choice over another just because it's what they
are used to.  For me personally the preference for unsigned index
types is not one of those.  But there can be value in having strong
habits even if the habits came about accidentally rather than as a
result of a considered conscious choice.