[R] converting R objects to C types in .Call
Is there a specific reason why, instead of CHAR(STRING_ELT(chstr, 0)); The S-Plus compatible CHARACTER_POINTER(chstr)[0] does not work in R? -- Edzer __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] converting R objects to C types in .Call
On Tue, 25 Jan 2005, Edzer J. Pebesma wrote: Is there a specific reason why, instead of CHAR(STRING_ELT(chstr, 0)); The S-Plus compatible CHARACTER_POINTER(chstr)[0] does not work in R? Yes. This is really a question for R-devel, but briefly, R and S-PLUS store character vectors in very different ways. This worked prior to 1.2.0, but was changed as part of the price of the new (then) garbage collector. -- Brian D. Ripley, [EMAIL PROTECTED] 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 272866 (PA) Oxford OX1 3TG, UKFax: +44 1865 272595 __ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
[R] converting R objects to C types in .Call
Dear People,
I'm trying to write an R wrapper for a C++ library, using .Call. I've
never used .Call before. I'm currently having some difficulties converting
a R character string to a C one.
Here is a little test program.
#include R.h
#include Rinternals.h
#include stdio.h
SEXP testfn(SEXP chstr)
{
char * charptr = CHAR(chstr);
printf(%s, charptr);
}
This compiles without problems, but when I try to run this as
.Call(testfn, foo)
I get a segmentation fault.
I am sure I am making an obvious mistake, but can someone help me to sort
it out? Thanks in advance. Please cc me, I'm not subscribed.
Faheem.
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Re: [R] converting R objects to C types in .Call
Faheem Mitha wrote:
SEXP testfn(SEXP chstr)
{
char * charptr = CHAR(chstr);
printf(%s, charptr);
}
I am sure I am making an obvious mistake, but can someone help me to
sort it out? Thanks in advance. Please cc me, I'm not subscribed.
Firstly, R is expecting an SEXP as a return value! And secondly, your
SEXP chstr is still a vector - so you need to get an element from it. If
there's only one element, then that'll be the zeroth element. Here's my
code:
#include R.h
#include Rinternals.h
#include stdio.h
SEXP testfn(SEXP chstr)
{
char * charptr = CHAR(VECTOR_ELT(chstr,0));
printf(%s, charptr);
return(chstr);
}
- I'm just returning the same object back in the return() statement,
and using VECTOR_ELT(chstr,0) to get to the 0'th element.
SO in R:
foo = .Call(testfn,fnord)
should print 'fnord' and return foo as fnord.
foo = .Call(testfn,c(bar,baz))
will print 'bar' and return foo as c(bar,baz)
Baz
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Re: [R] converting R objects to C types in .Call
On Mon, 24 Jan 2005, Faheem Mitha wrote:
I'm trying to write an R wrapper for a C++ library, using .Call. I've never
used .Call before. I'm currently having some difficulties converting a R
character string to a C one.
Here is a little test program.
#include R.h
#include Rinternals.h
#include stdio.h
SEXP testfn(SEXP chstr)
{
char * charptr = CHAR(chstr);
CHAR(STRING_ELT(chstr, 0));
First you select the first element of the character vector, then select
its contents as a C-level character array.
printf(%s, charptr);
}
This compiles without problems, but when I try to run this as
.Call(testfn, foo)
I get a segmentation fault.
I am sure I am making an obvious mistake, but can someone help me to sort it
out? Thanks in advance. Please cc me, I'm not subscribed.
Please read `Writing R Extensions' for more examples.
--
Brian D. Ripley, [EMAIL PROTECTED]
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 272866 (PA)
Oxford OX1 3TG, UKFax: +44 1865 272595
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Re: [R] converting R objects to C types in .Call
Hi Barry,
Thanks for your reply.
On Mon, 24 Jan 2005, Barry Rowlingson wrote:
Firstly, R is expecting an SEXP as a return value!
Ouch...
I haven't found anything that says this explicitly, but it looks like
.Call expects a SEXP to be returned to R. At any rate, trying to use void
instead gives a segfault.
And secondly, your SEXP chstr is still a vector - so you need to get an
element from it. If there's only one element, then that'll be the zeroth
element. Here's my code:
#include R.h
#include Rinternals.h
#include stdio.h
SEXP testfn(SEXP chstr)
{
char * charptr = CHAR(VECTOR_ELT(chstr,0));
printf(%s, charptr);
return(chstr);
}
- I'm just returning the same object back in the return() statement, and
using VECTOR_ELT(chstr,0) to get to the 0'th element.
SO in R:
foo = .Call(testfn,fnord)
should print 'fnord' and return foo as fnord.
foo = .Call(testfn,c(bar,baz))
will print 'bar' and return foo as c(bar,baz)
Thanks for your help. That works fine. Faheem.
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