There is no such problem, as R itself uses this construction repeatedly.
You are using a non-standard compiler, and also your example is incorrect,
as the recommended compiler warns.
On Thu, 22 Aug 2002, Vele Samak wrote:
> Ok, Here's the c code that's loaded into R as dll on windows:
>
> #include <R.h>
> #include <Rdefines.h>
> SEXP test1(SEXP col);
>
> SEXP test1(SEXP col)
> {
> SEXP col2;
> Rprintf("no value!\n");
> return col2;
> }
>
> Compiles ok with bcc32 into a dll, loads into R as part of a library, I
> Run library(rkdb), then
> > .Call("test1", 2)
> no value!
>
> And puf! Rterm crashes.
As it should. You have returned an unassigned pointer. Does your
compiler not warn you about such an error? The recommended one does:
gcc -Ic:/R/rw1060/src/include -Wall -O2 -c foo.c -o foo.o
foo.c: In function `test1':
foo.c:6: warning: `col2' might be used uninitialized in this function
> What's the point of this? I developed a library for connecting to a kdb
> database from within R. Similar to RODBC, but faster and more
> streamlined for access of real-time tick data. Everything works great,
> compiles on Win2000, R 1.3.1 and R 1.5.1 with Borland's free C++ 5.5,
> and runs into .dll.
Are you sure that R_NilValue is being linked correctly? It is an
exported variable from R.dll. There is a caveat in `readme.packages'
about this, and it is the usual cause of such problems.
> All functions work great except when there's no data
> from the database I do
> if (nrows <= 0) {
> Rprintf("No rows...");
> return R_NilValue;
> }
> And there lies the blow up of Rterm!!! Apparently R_NilValue can be
> assigned to any SEXP object internally, but when it's returned, Rterm
> doesn't know what to do with it.
It does if linked as recommended,
> I tried another bypass:
> SEXP NIL;
> if (nrows <= 0) {
> Rprintf("No rows...");
> return NIL;
> }
> This works in most but not all cases. Weird!
What's NIL?
> Any suggestions, comments are highly appreciated. Thanks,
--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
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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