Re: Variables in for loop (style issue)

Bob Hairgrove wrote:
  > On 6 May 2006 10:21:43 -0400, "kanze" <kanze@gabi-soft.fr> wrote:

  >> Bob Hairgrove wrote:
  >>
  >> [...]
  >>> One big problem is the fact that not all containers are
  >>> vectors, and calling size() is very inefficient for almost
  >>> all containers except for std::vector.

  >> Is it? His code in the loop said "do something with v[i]".
  >> What container supports v[i], and has an inefficient size()
  >> function.

  > Good point. I suppose they go hand in hand. My concerns here
  > were guided by what Scott Meyers says in "Effective STL" where
  > he recommends testing "if (v.empty())" instead of "if
  > (v.size())" where v can be a variable of just about any STL
  > container type.

Well, a perhaps more telling argument for using v.empty()
instead of v.size() != 0 is that it says more explicitly what
you are testing for.

  >>> How about this:
  >>> for (size_t i=0, std::vector<whatever_v_is>::iterator it = v.begin();
  >>> it != v.end(); ++i, ++it) {
  >>> // etc.
  >>> }
  >>> I think this solves all the above problems nicely.

  >> But introduces a new one: it's not legal C++, and won't
  >> compile.

  > Oops ... so we declare i outside of the loop, then it should
  > work (or did you see anything else wrong with it?)

Why i, and not it? For that matter, why use two variables, when
one will do the trick?

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James Kanze kanze.james@neuf.fr
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