Re: Fortran character strings

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Subject: Re: Fortran character strings
From: Kurt Hornik (Kurt.Hornik@ci.tuwien.ac.at)
Date: Thu 09 Sep 1999 - 18:14:54 EST


Message-ID: <14295.27774.194390.155680@fangorn.ci.tuwien.ac.at>

>>>>> 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.)

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

-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?

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