Re: const local variables

[Bruno Haible]

James Youngman wrote:
> * lib/close-stream.c (close_stream): Make boolean variables const
> to document the fact that we set but do not change them.
> --- a/lib/close-stream.c
> +++ b/lib/close-stream.c
> @@ -55,9 +55,9 @@
>  int
>  close_stream (FILE *stream)
>  {
> -  bool some_pending = (__fpending (stream) != 0);
> -  bool prev_fail = (ferror (stream) != 0);
> -  bool fclose_fail = (fclose (stream) != 0);
> +  const bool some_pending = (__fpending (stream) != 0);
> +  const bool prev_fail = (ferror (stream) != 0);
> +  const bool fclose_fail = (fclose (stream) != 0);

There are programming languages where this style of using 'const' may
be customary (like C++ or Java), but I don't think it helps in C code:
  1) For the person reading the code, it draws the attention away from
     more importants parts of the code.
  2) For the person modifying the code, it requires additional attention,
     to remember to remove 'const' here and there. That's frequent in C,
     because the vast majority of code in C is written in style that
     modifies local variables (as opposed to functional style).

If you find yourself looking at a function where you don't overlook
all the uses of a variable, then my advice would be to
  a) use an IDE which shows you all uses of a local variable on
     demand (Eclipse can do that, and José Marchesi knows how to do
     that with Emacs),
  b) limit the scope of the variables. Create intermediate blocks
     that declare variables for the minimum possible scope.

Bruno