Re: gnuplot slow on BIG files

[Ethan M. <merritt@u.washington.edu>]

On Thursday 09 June 2005 12:26 am, Hans-Bernhard Br=F6ker wrote:
> Ethan Merritt wrote:
>=20
> There's not a lot you could do with strtod() that sscanf() couldn't do=20
> just as well.

But slower, apparently.

> >>sscanf() and its %n format are used for a reason.
>=20
> > But %n is non-portable, as documented by the OSK comment=20
>=20
> Just because some silly implementation is buggy doesn't exactly mean %n=20
> is unportable.  %n is as portable as you can ever hope to be: it's an=20
> ANSI requirement.

Surely you know the quote about standards: "Standards are nice because
there are so many of them...".  =20
It turns out that different ANSI revisions describe
the behavior of %n differently, so it is not portable.  Here is an=20
excerpt from the current man page:
  "Probably  it  is  wise not  to  make any assumptions on the
   effect of %n conversions on the return value."

The current code assumes that=20
	count =3D sscanf(s, "%lf%n", ...)
will set count to 1 if successful, but on some systems it will instead
set count to 2.  I do not know if this is the specific problem with OSK.

strtod() is more portable than %n, and allows more complete=20
error reporting than sscanf().
=20
> I dimly remember this being about not running sscanf() on all columns of=
=20
> a multi-column data file if no extended using specs are in use.  If you
> have "using 1:2:3", you can simply ignore columns 4 to 1000.  If you=20
> have "using 1:2:(column(some_function($3)), datafile.c has to convert=20
> all 1000 of them.

That is an interesting point, and I now wonder if these optimization lines
conflict with the new column-based syntax elements like xticlabels().
I will have to experiment with this.


=2D-=20
Ethan A Merritt       merritt@u.washington.edu
Biomolecular Structure Center
Mailstop 357742
University of Washington, Seattle, WA 98195