[gmx-developers] Re: gmx-developers Digest, Vol 96, Issue 16

[Roland Schulz]

On Wed, Apr 11, 2012 at 9:50 AM, Szilárd Páll <szilard.pall at cbr.su.se>wrote:

> On Wed, Apr 11, 2012 at 3:16 PM, Peter Kasson <kasson at stanford.edu> wrote:
> >> Date: Wed, 11 Apr 2012 14:33:09 +0200
> >> From: Erik Marklund <erikm at xray.bmc.uu.se>
> >> Subject: Re: [gmx-developers] Coordinate scaling in pdbio.c
> > [...]
> >>>>>>> What happened to A2NM and NM2A?
> >>>>>>> In my (4.0.5, yes that is very old) includes/physics.h I still see:
> >>>>>>>
> >>>>>>> #define A2NM (ANGSTROM/NANO) /* NANO */
> >>>>>>> #define NM2A (NANO/ANGSTROM) /* 10.0 */
> >>>>>>>
> >>>>>>> Why aren't these still used for that?
> >>>>>>>
> >>>>>>>
> >>>>>> At some stage macros were removed from the code, even though these
> seem rather harmless. I agree that it is confusing to hard code these
> numbers. If we cannot use macro's like this we should probably replace them
> by
> >>>>>> static const real ANGSTROM=1e-10;
> >>>>>> static const real NANO=1e-9;
> >>>>>>
> >>>>>> etc.
> >>>>>>
> >>>>>> Comments?
> >>>>>
> >>>>> include/physics.h still has these macros. IMO, hard-coded constants
> are a greater evil than macros to prevent that, though I expect we will
> transition to const values at some stage soon.
> >>>>
> >>>> But are these the kind of macros we want to avoid? Aren't
> function-like macros the ones to kill in the first place?
> >>>  They're taking no parameters, so they're hardly function-like. The
> code fragments above are compiled into constants by the pre-processor. A
> macro that is used as
> >>>
> >>> dist_in_nm = dist_in_angstrom * A2NM;
> >>>
> >>> is much less evil than a macro
> >>>
> >>> dist_in_nm = A2NM(dist_in_angstrom);
> >>
> >> My point exactly. I'm just not seeing the harm in using macros in cases
> like these.
> >
> > Consts are preferred (not #defines but actual consts).
> >
> >
> http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml#Preprocessor_Macros
>
> That's C++ and we're not there yet. For 4.6 IMO it makes sense to
> clarify code by replacing "x/10.0" with "x/A2NM". In fact, this will
> help with the transition to constants later.
>

What's wrong with using "const" constants in C?

Roland


>
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> Szilárd
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