Re: Fortran character strings

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Subject: Re: Fortran character strings
From: Prof Brian D Ripley (
Date: Thu 09 Sep 1999 - 18:28:24 EST

Message-ID: <Pine.GSO.4.05.9909090916450.4120-100000@auk.stats>

On Thu, 9 Sep 1999, Kurt Hornik wrote:

> >>>>> Prof Brian Ripley writes:
> > Has anyone ever successfully used Fortran character strings with R?
> > ?Foreign says
> > R C Fortran
> > integer int * integer
> > ....
> > character char ** [compiler dependent]
> > Character strings are passed as C arrays of character
> > strings to Fortran: the first string may be usable if
> > its length is passed separately.
> > and I have been taking a look. The linkage sends char ** to Fortran.
> > On the other hand, INTPR and DBLEPR assume Fortran character strings
> > are char *. On all my systems DBLEPR works and .Fortran does not, but
> > I do know of one compiler (Watcom Fortran for Windows NT) where the
> > linkage really is equivalent to char **.
> > Fortran in S takes the first string in a character vector and passes
> > that as char * (except on the Watcom-compiled Windows version), as far
> > as I can deduce without the source code.
> > I think we should either ban character strings in .Fortran or follow
> > the S prototype unless someone has a way around this. With different
> > compilers on the same platform having different conventions whatever
> > we do (except a ban) will be compiler-dependent.
> > Any suggestions?
> Hmm ... this is someone not knowing what is going (i.e., me) commenting
> on this.
> I touched this once when porting Rousseeuw's cluster routines to R,
> maybe the thread is in the r-core archives. I seem to recall that
> someone told me that this was really a compiler-specific issue and hence
> could/should not be part of the API. (In the specific case, it was a
> 0/1 string so I found a different solution.)

It is compiler-specific, but there is a solution that works in 99% of the
cases that I have put in R-devel, with warnings.

> (Btw, why do we map integer to int * and not long *?)

How would I know? (Actually, because it lets us use the C linakge, I
guess.) We do assume that in building R, for things like eigen. I noted
that f2c does have a configure check for this, and I think we probably
ought to find out at configure time what integer does map to and make
.Fortran cover this.

> -k
> PS. A comment on ?.External: We have
> list void * (SEXP *)
> other void * (SEXP)
> I think this (showing the alternative in parenteses) may be confusing.
> Shouldn't we show the preferred method in the table and mention the
> alternative somewhere in the text following?

It is confusing. Actually all of them are mapped to void *, so I think we
should be giving SEXP * and SEXP. Thomas?

Brian D. Ripley,        
Professor of Applied Statistics,
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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